rp756draft13

Management of Hazards Associated with Location of Process Plant Tents API RECOMMENDED PRACTICE 756 FIRST EDITION,

DRAFT 13

COMMITTEE DRAFT

II API RECOMMENDED PRACTICE 756

FOREWORD

This recommended practice (RP) provides guidance for tent siting evaluation. It references API RP 752 and API

RP 753 and other documents concerning technical aspects of siting evaluation including hazard identification,

consequence modeling, structural analysis, and risk. Among the hazards that potentially could affect tent occupants

are explosion, fire, and toxic material releases.

Nothing contained in any API publication is to be construed as granting any right, by implication or otherwise, for the

manufacture, sale, or use of any method, apparatus, or product covered by letters patent. Neither should anything

contained in the publication be construed as ensuring anyone against liability for infringement of letters patent.

Shall: As used in an RP, “shall” denotes a minimum requirement in order to conform to the RP.

Should: As used in an RP, “should” denotes a recommendation or that which is advised but not required in order to

conform to the RP.

This RP was produced under API standardization procedures that ensure appropriate notification and participation in

the developmental process and is designated as an API Recommended Practice. Questions concerning the

interpretation of the content of this publication or comments and questions concerning the procedures under which

this publication was developed should be directed in writing to the Director of Standards, American Petroleum

Institute, 1220 L Street, NW, Washington, DC 20005. Requests for permission to reproduce or translate all or any

part of the material published herein should also be addressed to the director.

Generally, API RPs are reviewed and revised, reaffirmed, or withdrawn at least every five years. A one-time

extension of up to two years may be added to this review cycle. Status of the publication can be ascertained from

the API Standards Department, telephone (202) 682-8000. A catalog of API publications and materials is published

annually by API, 1220 L Street, NW, Washington, DC 20005.

Suggested revisions are invited and should be submitted to the Standards Department, API, 1220 L Street, NW,

Washington, DC 20005, [email protected].

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MANAGEMENT OF HAZARDS ASSOCIATED WITH LOCATION OF PROCESS PLANT TENTS III

Contents

1 Scope ...................................................................................................................................... 1 1.1 General .............................................................................................................................................................. 1 1.2 Guiding Principles ............................................................................................................................................. 1 1.3 Relationship with API RP-752 and API-753 ..................................................................................................... 1

2 Normative References ........................................................................................................... 2

3 Terms and Definitions ........................................................................................................... 2 3.1 Blast Load .......................................................................................................................................................... 2 3.2 Consequence .................................................................................................................................................... 2 3.3 Consequence-Based Approach........................................................................................................................ 2 3.4 Essential Personnel .......................................................................................................................................... 2 3.5 Fabric ................................................................................................................................................................. 2 3.6 Hazard ............................................................................................................................................................... 2 3.7 Maximum Credible Event (MCE) ..................................................................................................................... 3 3.8 Occupant Vulnerability ...................................................................................................................................... 3 3.9 On-Site Personnel ............................................................................................................................................. 3 3.10 Process Area ..................................................................................................................................................... 3 3.11 Quantitative Risk Assessment .......................................................................................................................... 3 3.12 Risk .................................................................................................................................................................... 3 3.13 Risk-Based Approach ....................................................................................................................................... 3 3.14 Spacing Tables Approach ................................................................................................................................. 3 3.15 Tent .................................................................................................................................................................... 3 3.16 Tent Siting Evaluation ....................................................................................................................................... 7 3.17 Turnaround (TA) ................................................................................................................................................ 7 3.18 Toxic Material .................................................................................................................................................... 7 3.19 Vapor Cloud Explosion (VCE) .......................................................................................................................... 7

4 Determination of Tents Requiring Tent Siting Evaluation ................................................ 7 4.1 Tents Included in the Siting Evaluation ............................................................................................................ 7 4.2 Tents Excluded from the Siting Evaluation ...................................................................................................... 8 4.3 Tents Evaluated on a Case-by-case Basis ...................................................................................................... 8

5 Tent Siting Evaluation Processes ........................................................................................ 9 5.1 Work Process Overview .................................................................................................................................... 9 5.2 General Tent Siting Evaluation Processes ..................................................................................................... 11

5.2.1 Tent Siting Evaluation Criteria ................................................................................................................ 11 5.2.2 Siting Evaluation of Tents ....................................................................................................................... 11 5.2.3 Selection of Assessment Approach ....................................................................................................... 11 5.2.4 Additional Guidance for Turnaround/Project Construction Meal Tents ................................................ 11 5.2.5 Scenario Selection for Consequence-based and Risk-based Approaches .......................................... 12

5.3 Additional Design and Siting Requirements for Tents Included in the Siting Evaluation Study ................... 12 5.4 Considerations for Tents Excluded from the Siting Evaluation Study ........................................................... 13 5.5 Personnel Performing Tent Siting Evaluation ................................................................................................ 13 5.6 Management of Tent Occupancy ................................................................................................................... 13 5.7 Implementation and Change Control .............................................................................................................. 14 5.8 Documentation ................................................................................................................................................ 15

6 Tent Siting Evaluation for Explosion ................................................................................. 15 6.1 Work Process Overview .................................................................................................................................. 15 6.2 Tent Siting Methodology ................................................................................................................................. 17 6.3 Detailed Structural Analysis ............................................................................................................................ 18 6.4 Explosion Testing ............................................................................................................................................ 19 6.5 Measures to Reduce Occupant Vulnerability from Explosions ..................................................................... 19

7 Tent Siting Evaluation for Fire ........................................................................................... 20 7.1 Work Process .................................................................................................................................................. 20 7.2 Egress and Evacuation for Fire ...................................................................................................................... 20

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IV API RECOMMENDED PRACTICE 756

8 Tent Siting Evaluation for Toxic Material Release ........................................................... 20 8.1 Work Process .................................................................................................................................................. 20 8.2 Egress and Evacuation for Toxic Material Release ....................................................................................... 21

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Management of Hazards Associated with Location of Process Plant Tents

1 Scope

1.1 General

This recommended practice (RP-756) provides guidance for managing the risk from explosions, fires and toxic

material releases to on-site personnel located in tents. The term “tent” is used to describe a wide range of structures

and is defined in §3.15. This RP was developed for use at refineries, petrochemical and chemical operations,

natural gas liquids extraction plants, natural gas liquefaction plants, and other onshore facilities covered by OSHA 29

CFR 1910.119 [Reference 1].

The focus of this RP is primarily on assessing the potential impact to tent occupants from process related hazards.

However, non-process related tent hazards may exist which could present risks to tent occupants. Previous

accidents have demonstrated that tent occupants are susceptible to injuries from fires originating inside the tent,

from tent collapse due to extreme weather, and from falling objects. Some of these hazards are managed by tent

design standards, manufacturer’s recommendations, and local regulations. See §5.3 for additional guidance.

1.2 Guiding Principles

This RP is based on the following guiding principles:

a) Locate personnel away from process areas consistent with safe and effective operations.

b) Minimize the use of tents intended for occupancy in close proximity to process areas.

c) Manage the occupancy of tents in close proximity to process areas.

d) Design, construct, install, modify, and maintain tents intended for occupancy to mitigate hazards that the tent

siting could present to occupants in the event of explosion, fire, and toxic material release.

e) Manage the use of tents intended for occupancy as an integral part of the design, construction, maintenance, and

operation of a facility.

1.3 Relationship with API RP-752 and API-753

The requirements and work processes in API RP-756 are similar to API RP-752, “Management of Hazards

Associated with the Location of Process Plant Permanent Buildings.” API RP-756 uses a similar zoning concept for

design/site selection decisions as API RP-753 “Management of Hazards Associated with the Location of Process

Plant Portable Buildings.” API RP-756 was written using the same language in API RP-752 for consistency between

the two documents. In many cases API RP-756 refers to API RP-752 and API RP-753 for detailed guidance rather

than duplicate the guidance here.

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2 API RECOMMENDED PRACTICE 756

2 Normative References

The following are normative references for this RP:

“Management of Hazards Associated with Location of Process Plant Permanent Buildings,” API

Recommended Practice 752, 3rd edition

“Management of Hazards Associated with Location of Process Plant Portable Buildings,” API

Recommended Practice 753, 1st edition

“Temporary Structures – Tents – Safety,” EN 13782

References in this RP and the bibliography other than the normative references listed above are provided for

information only and are not part of this RP.

3 Terms and Definitions

For the purpose of this publication, the following terms and definitions apply.

3.1 Blast Load

The load applied to a structure or object from a blast wave, which is described by the combination of overpressure

and either impulse or duration.

3.2 Consequence

The potential effects of an explosion, fire, or toxic material release. Consequence descriptions may be qualitative or

quantitative.

3.3 Consequence-Based Approach

The methodology used for tent siting evaluation that is based on the impact of explosion, fire, and/or toxic material

release and which does not consider the frequency of these events

3.4 Essential Personnel

Onsite personnel with specific work activities that require them to be located in tents in or near a process area for

logistical and response purposes. The identification of essential personnel will vary with operation and work

activities including normal operation, start-up, and planned shutdown. Examples of essential personnel include, but

are not limited to, craftspeople, operators, and maintenance personnel. Examples of persons who are not essential

personnel include, but are not limited to, designers, timekeepers, clerical staff, administrative support, and

procurement staff.

3.5 Fabric

Any flexible material used for the covering or enclosure of the tent.

3.6 Hazard

An inherent physical or chemical characteristic (e.g., flammability, toxicity, corrosivity, stored chemical energy, or

mechanical energy) that has the potential for causing harm to people, property, or the environment.

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MANAGEMENT OF HAZARDS ASSOCIATED WITH LOCATION OF PROCESS PLANT TENTS 3

3.7 Maximum Credible Event (MCE)

A hypothetical explosion, fire, or toxic material release event that has the potential maximum consequence to the

occupants of the tent under consideration from among the major scenarios evaluated. The major scenarios are

realistic and have a reasonable probability of occurrence considering the chemicals, inventories, equipment and

piping design, operating conditions, fuel reactivity, process unit geometry, industry incident history, and other factors.

Each tent may have its own set of MCEs for potential explosion, fire, or toxic material release impacts.

3.8 Occupant Vulnerability

Proportion of tent occupants that could potentially experience a life threatening injury or fatality if a potential event

were to occur.

3.9 On-Site Personnel

Employees, contractors, visitors, service providers, and others present at the facility.

3.10 Process Area

An area containing equipment (e.g., pipes, pumps, valves, vessels, reactors, and supporting structures) intended to

process or store materials with the potential for explosion, fire, or toxic material release.

3.11 Quantitative Risk Assessment

The systematic development of numerical estimates of the expected frequency and consequence of potential

accidents based on engineering evaluation and mathematical techniques. The numerical estimates can vary from

simple values of probability/frequency of an event occurring based on relevant historical industry or other available

data to very detailed frequency modeling techniques.

3.12 Risk

A measure of potential injury, environmental damage, or economic loss in terms of both the incident likelihood and

the severity of the loss or injury.

3.13 Risk-Based Approach

A quantitative risk assessment methodology used for tent siting evaluation that takes into consideration numerical

values for both the consequences and frequencies of explosion, fire, or toxic material release.

3.14 Spacing Tables Approach

The “spacing tables” approach uses established tables to determine minimum separation distances between

equipment and tents. Industry groups, insurance associations, regulators, and owner/operator companies may have

experience-based spacing tables that are useful for establishing minimum tent spacing for fire.

3.15 Tent

The term “tent” is used to describe a wide range of structures. These structures include traditional tents with or

without sides (canopy), air inflated structures, air supported structures, tensioned membrane tents, scaffold

structures, or structures that use a combination of fabric and rigid panels. Some of these tent types are defined

below:

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— Traditional tent: a fabric covered structure, enclosure or shelter that achieves its support by mechanical

means such as columns, beams, poles or arches, rope or cables, or some combination of these.

— Air inflated structure: a structure in which the shape is maintained by air pressurization of cells or tubes to

form a barrel vault over the usable area. The pressurized areas used to support the structure are not occupied.

See Figure 1 below for an example.

Figure 1. Example of Air Inflated Structure (Top – Exterior View, Bottom – Crossectional View)

— Air-supported structures: a structure in which the shape is attained by air pressure, and occupants of this

structure are within the pressurized area.

— Scaffolding tent: a self-supported structure built with scaffolding components or similar materials and

enclosed with a fabric. See Figure 2 below for examples of scaffolding tents. COMMITTEE DRAFT


Figure 2. Examples of Scaffolding Tents

— Pole tent: a fabric covered structure that achieves its support by use of columns/poles and is stabilized along

the perimeter with ropes/cables. Pole tents are available in wind-rated and non-wind-rated designs. See

Figure 3 for examples of pole tents.

Figure 3. Examples of Pole Tents

— Light frame tent: in general is a fabric covered structure that uses a frame to maintain its shape and is

stabilized along the perimeter with ropes/cables. Unlike pole tents, the light frame tents have no center poles.

Structural members are located around the perimeter and the upright members are rigidly secured to the roof

frame members. Light frame tents are available in wind-rated and non-wind-rated designs. See Figure 4 for an

example of a light frame tent.

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Figure 4. Example of Light Frame Tent

— Tensioned membrane tents: a structure incorporating a membrane and a structural support system such as

arches, columns, and cables or beams. The stresses developed in the tensioned membrane interact with

those in the structural support so that the entire assembly acts together to resist the applied load. Tension

membrane tents differ from light frame tents in that:

Tension membrane tents have a much more robust frame,

The frame is directly anchored to the ground (no staked ropes/cables along the perimeter), and

The fabric is taut.

Most, if not all, tension membrane tents are wind-rated. See Figure 5 below for examples of tension membrane

tents.

Figure 5. Examples of Tension Membrane Tents

— Engineered tent: A tent that has been pre-engineered to meet a specific design code.

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— 90 mph Tent: A Tent that is rated and certified to meet a 70-mph sustained wind and a 90-mph three-second

gust of wind

— Improvised tent: a make-shift non-manufactured tent, not covered by other tents described above

3.16 Tent Siting Evaluation

The procedures described in this RP that are used to site tents given their performance characteristics and the

hazards at the specific tent location.

3.17 Turnaround (TA)

A work activity where an entire process unit or a major section of a unit is shutdown for a period of time for the

purpose of inspection, maintenance, or modification.

3.18 Toxic Material

An airborne agent that could result in acute adverse human health effects.

3.19 Vapor Cloud Explosion (VCE)

The explosion resulting from the ignition of a cloud of flammable vapor, gas, or mist in which the flame speed

accelerates to sufficiently high velocities to produce a damaging blast wave.

4 Determination of Tents Requiring Tent Siting Evaluation

4.1 Tents Included in the Siting Evaluation

Tents intended for occupancy shall be included in the tent siting evaluation. A tent intended for occupancy has

personnel assigned to it, or is used for a recurring personnel function.

Examples of tents that have personnel assigned include, but are not limited to:

Guardhouses, tool stations, maintenance shops, field operator shelters, offices, laboratories, or

warehouses.

Tents for fabrication, welding, or equipment assembly that can be performed remotely from the process unit.

Examples of tents used for a recurring personnel function include, but are not limited to functions such as:

Breaks or meals.

Change houses, orientation, training, or meetings.

Weather shelters (e.g., cool down and warm-up tents) unless excluded in 4.2(e).

Certain tents may be excluded from the evaluation as described in §4.2. Buildings that are located inside of tents

are covered by either API RP-752 or API RP-753, as applicable.

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4.2 Tents Excluded from the Siting Evaluation

Examples of tents that are excluded from the tent siting evaluation are as follows.

a) Temporary tents that provide weather protection or regulatory compliance (e.g., asbestos or lead paint

remediation) as their primary function for equipment or work activities that cannot be feasibly performed remotely

from the process unit or equipment. Examples of such work activities in these temporary tents include, but are

not limited to:

Insitu welding on installed equipment/piping

Non Destructive Testing (NDT) of installed equipment/piping

Insitu hazardous materials abatement or decontamination

Catalyst loading and unloading

Weather protection of equipment such as vessels, compressors, turbines, etc.

b) Tents that enclose process areas where only essential personnel are assigned to perform activities similar to

those performed at an outdoor process area. The basis for excluding such tents is the recognition that certain

work activities must be performed in or near the process area (e.g., a tent enclosing an operating compressor).

c) Individual small, lightweight tents (i.e., less than 150 sq ft). The basis for excluding such tents is that the number

of occupants is low; the components are lightweight and the risks inside and outside the tent may not be

different. Installation of multiple small contiguous tents to perform the function of a larger tent is not allowed by

this exclusion.

d) Tents that require intermittent access. The basis for excluding such tents is that a person would only spend a

relatively small amount of time inside the tent and only a few people would be present at any one time. Examples

of such tents include, but are not limited to:

Tents intended to protect equipment or product (with no personnel assigned).

Field sampling/testing/analyzer stations

Hydration stations (a shaded area that provides access to liquids with no other amenities).

Safety shower tents.

e) Temporary cool-down or warm-up tents intended to meet owner/operator industrial hygiene requirements for

extreme environmental conditions (e.g., where people can work in the environment for 5 minutes, but need time

inside the tent for thermal recovery). Unlike the cool down and warm-up tents described in 4.1, these tents may

be excluded on the basis of: they are occupied only by essential personnel, locating the tent further away would

increase extreme heat/cold exposure to these personnel, and use of alternatives (such as Blast Resistant

Modules) is not feasible.

Tents that are excluded from the tent siting evaluation shall not be used by personnel for other than the intended use

(e.g., a welding shelter shall not be used as a break area).

4.3 Tents Evaluated on a Case-by-case Basis

Tents that do not meet the descriptions provided in §4.1 or 4.2 above may be included or excluded in the tent siting

evaluation on a case-by-case basis. The basis for inclusion or exclusion should consider the hazards, the number of

tent occupants, how much time (frequency and duration) occupants are in the tent, and the purpose of the tent.

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5 Tent Siting Evaluation Processes

5.1 Work Process Overview

The work process for tent siting evaluations can be summarized in four steps:

1. Identify tents that are to be included in the siting evaluation study.

2. Evaluate these tents against potential explosion, fire, and toxic impacts.

3. Determine if tent design/siting meets the owner/operator’s tent siting evaluation criteria and mitigate those

that do not.

4. Apply the additional design/siting requirements (see §5.3).

Tents excluded from the siting evaluation study may consider the siting/layout suggestions in §5.4. See Figure 6 for

an overview of the tent siting evaluation work process.

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Figure 6. Work Process: Tent Siting Evaluation

START

Does tent provide

only weather protection for

equipment or product?

(4.2.a,b)

Yes

Yes

Does the tent meet the

criteria for case-by-case

exclusion (4.3)?

No

Select assessment

approach (§5.2.3)

Mitigate

Owner/Operator

criteria met?

STOP

No

No

Yes

Yes

Yes

Does tent meet

“intended for occupancy”?

(4.1)

Comply with additional

design and siting

requirements (5.3), and

implement tent occupancy

management (5.6) and

MOC (5.7)

Tent is excluded from

the tent siting evaluation

study. Consider general

siting requirements (5.4)

Is the tent small and

lightweight (4.2.c) or

require only intermittent access

(4.2.d) or meet criteria for

cool-down / warm-up tents

(4.2.e)?

No

No

Assess explosion, fire, and toxic

hazards:

Explosion Hazard (§6)

Fire Hazard (§7)

Toxic Hazard (§8)

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5.2 General Tent Siting Evaluation Processes

5.2.1 Tent Siting Evaluation Criteria

Prior to starting a tent siting evaluation, owners/operators should select tent siting evaluation criteria consistent with

the selected assessment approach(es) described in §5.2.3 below. Refer to API RP-752 Section 5.3 for a description

of the evaluation criteria for each of the assessment approaches.

5.2.2 Siting Evaluation of Tents

Owners/operators shall carry out siting evaluations for tents included in the tent siting evaluation in accordance with

Section 6, 7, and 8 of this RP. Additional tent design/siting requirements are provided in §5.3

5.2.3 Selection of Assessment Approach

Owners/operators may choose one or more of the following approaches for assessing explosion, fire and toxic

material release scenarios.

a) The “consequence-based” approach evaluates the impact of explosion, fire, and toxic material release scenarios.

This approach shall be based on maximum credible events (MCEs) for each tent and type of hazard considered.

Owners/operators may choose to develop site-specific spacing distances for each type of tent considered to

cover explosions, fires, or toxic material release. These distances shall be based on MCEs. The use of site

specific, MCE based spacing distances is considered an application of a consequence-based approach.

b) The “risk-based” approach is quantitative and utilizes numerical values for both the consequences and the

frequencies of explosion, fire, and toxic material release scenarios.

The consequence-based and risk-based approaches may range from simple to complex analyses. Complex

analyses can take into account details of the site layout, geometry, and the scenarios. Simplified analyses should

use conservative assumptions as a means to account for the details not included in the analyses. Additional

guidance may be found in Sections 6, 7, and 8 of this RP.

5.2.4 Additional Guidance for Turnaround/Project Construction Break/Meal Tents

Process unit maintenance turnarounds and major project construction activities (e.g., construction of a new process

unit) may require a large number (e.g., hundreds) of crafts-persons to work in areas which may be adjacent to or

surrounded by operating process units. Often tents exclusively for crafts-person’s breaks and meals are provided.

However, available siting options for these tents may present significant trade-offs. Where that is the case, the

owner/operator may choose to assess the tent siting in greater detail provided that this assessment is quantitative

and documented. Factors that may be considered when assessing turnaround/project construction break/meal tent

design/siting include but are not limited to:

The distance between the break/meal tent and the work location: Larger travel distances can result in longer travel time. The cumulative effect of long travel times can result in increased total personnel exposure to hazards since the time lost with transit will be made up either by extended schedule (increased exposure time) or additional crafts-persons (increased number of people exposed). Mitigating this by providing vehicle transport, however, introduces transportation risks.

The route between the break/meal tent and the work location: Hazard exposures from adjacent operating areas while in transit may be different from the work location or the break/meal tent location.

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Tent Occupancy: By limiting the tent function to breaks/meals, individuals in the tent would occupy it only for a short period of time (individual risk might be low). However, large numbers of people could be in the tent at any one time, and sequenced use (e.g., staged meals) could result in large numbers of people in the tent for a large portion of the time. Also, if the tent location is convenient, there may be a tendency to use the tent for other meetings and activities as well.

Exposures may vary over time: Hazards/risk may increase over time if the project construction results in new areas of process equipment congestion or when units which are shutdown for the turnaround are restarted.

Relative exposures: Hazards/risk exposures to crafts-persons in these tents may be compared to their hazards/risk exposures at the work location itself (at the unit under construction or the unit undergoing the turnaround activities).

The owner/operator may choose to take these and other factors into account when applying the approaches described in 5.2.3 for turnaround and project construction break/meal tents.

5.2.5 Scenario Selection for Consequence-based and Risk-based Approaches

The scenario selection process includes, where applicable, hazards associated with the operations including, but not

limited to, loss of containment, releases from flares, process vent stacks, and atmospheric relief devices.

The scenarios should be based primarily on the process area-specific factors such as equipment failure rate data,

design of the equipment in the process area, process stream composition, and operating conditions. Consideration

should be given to relevant company and industry loss of containment data for similar types of processes and

equipment when selecting scenarios. Start-up, shutdown and emergency shutdown situations should be included in

the scenario selection process. A review of the process hazard analysis (PHA) may assist in identifying scenarios.

5.3 Additional Design and Siting Requirements for Tents Included in the Siting

Evaluation Study

Owners/operators shall verify that all tents included in the siting evaluation:

Comply with any activity limitations (e.g., restrictions on equipment with open flames inside the tent),

occupancy loading, design, or spacing and siting requirements from local and national/jurisdictional fire

codes.

Provide adequate tent egress/exits. This may be covered by fire codes (e.g., NFPA 101 Life Safety Code

[Reference 8] and NFPA 102 Standard for Grandstands, Folding and Telescoping Seating, Tents and

Membrane Structures [Reference 9]) or company policy.

Restrict placement in the dike, berm or bund areas of storage tanks containing flammable, combustible or

toxic material.

Use fire resistant fabrics consistent with applicable fire codes and local standards.

Sited consistent with the owner/operator’s safe working practices.

Owners/operators shall consider potential hazards when siting tents. These include, but are not limited to, the

following:

Proximity to flares, vent stacks, and atmospheric relief valves.

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Proximity to sewers and vents.

Proximity to cranes, heavy lift activities, and vehicle traffic.

Obstructions to escape routes by tent components (e.g., guy wires should be marked/flagged to mitigate

potential tripping hazard).

It should be recognized that some tents are not designed for significant weather events (lightning, high winds, snow

storms, etc.) and all tents have limits to their structural capacity. Owners/operators shall consider local

environmental conditions and local building codes when selecting, constructing, and maintaining tents.

Owners/operators should have a procedure in place to evacuate a tent in the event that environmental loading could

exceed the tent’s structural capacity.

5.4 Considerations for Tents Excluded from the Siting Evaluation Study

Owners/operators should consider local environmental conditions and applicable building codes when selecting,

constructing, and maintaining these tents. These tents should be sited consistent with the owner/operator’s safe

work practices.

Owners/operators may consider the following potential hazards when siting these tents:

Proximity to flares, vent stacks, and atmospheric relief valves.

Proximity to sewers and vents.

Proximity to fire and toxic exposures.

Proximity to cranes, heavy lift activities, and vehicle traffic.

Obstructions to escape routes by tent components (e.g., guy wires should be marked/flagged to mitigate

potential tripping hazard).

5.5 Personnel Performing Tent Siting Evaluation

Siting of tents is an important task and requires appropriate consideration of technical data regarding the

performance of tents when exposed to explosions, fires, or toxic releases. While methods are available in this RP to

establish standoff distances, the importance of siting tents requires that decisions be made by appropriate, qualified

personnel. Some options for performing detailed analysis for the siting of tents can involve specialized analysis

tools. Owners/operators shall establish a procedure or work process regarding tent siting approval and identify

personnel who are responsible for the tent siting evaluation.

5.6 Management of Tent Occupancy

Owners/operators shall develop procedures and practices that are designed to control the use of tents by personnel.

Consideration should be given to locating nonessential personnel as far as practicable from the hazard and

discouraging congregation of personnel in tents close to process areas.

Owner/operators should periodically confirm that tents are being used as intended, and the tent siting should be re-

evaluated if the intended use changes.

Tents should be taken down or secured (e.g., locked) when no longer needed.

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5.7 Implementation and Change Control

This recommended practice provides information that may be used when establishing or updating work processes or

procedures concerning the siting of tents. Specific tent siting guidelines and procedures for managing change shall

be developed for the use and location of tents. Examples of changes that should be managed include:

Changes to plant operations, processes or equipment (including decommissions or additions) that cause a

change in the potential for, or severity of, explosion, fire, or toxic impacts at the location of the tent. In

particular, when a tent that was sited taking into account shutdown of a process unit and that unit will now

be brought back online.

Addition of a new tent to the facility.

A modification or addition to an existing tent occurs that could cause a change in the impact from explosion,

fire, or toxic material release.

A change in the occupancy status or function of a tent.

If a tent is to be relocated.

If the number of personnel or time spent inside the tent increases either permanently or for a defined period

of time.

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5.8 Documentation

Owners/operators shall document the following elements of the siting evaluation:

Tent siting evaluation criteria (see §5.2.1);

Assessment approach (see §5.2.3);

Scenario selection basis (see §5.2.5);

Analysis methodologies (see Sections 6, 7, and 8);

Applicability of analysis methodologies;

Data sources used in the analysis;

Applicability of data sources; and

Results of the analysis for tents included in the tent siting evaluation.

Where specific features (e.g., heating, ventilation or air conditioning (HVAC), blast resistance, gas detection system,

and/or safety instrumented systems are used to meet the siting evaluation criteria), the performance and/or design

requirements shall be documented. These specific features shall be monitored and maintained over the life cycle of

the tent. Where procedures are used to meet the siting evaluation criteria, it shall be verified that they are

implemented, effective, and continuously applicable while the tent is in use.

6 Tent Siting Evaluation for Explosion Tents included in the tent siting evaluation shall be sited and of a design that meets the owner/operator’s tent siting

evaluation criteria for explosion.

6.1 Work Process Overview

This work process is applicable to those tents that are included in the tent siting evaluation using the general tent

siting evaluation process described in §5.2, and is shown in Figure 7.

Owners/operators shall determine if the tent could be impacted by explosion. Where no potential explosion scenario

is identified which could adversely affect the tent under consideration, a siting evaluation for explosion is not

required; however the determination shall be documented.

COMMITTEE DRAFT


Figure 7. Work Process: Tent Siting Evaluation for Explosion

The work process for explosion evaluation is identical to that described in Section 6 of API RP-752, with the

following differences:

1. The analysis may account for the reduced explosion potential of process areas that are shut down and de-

inventoried for the entire time the tent is occupied. See B.1.4 in API-753 for guidance on evaluating the

hazard of drifting vapor clouds from adjacent process units.

2. Structural analysis methods specific to tents are utilized (see §6.3).

3. Tent testing may be used in lieu of structural analysis (see §6.4).

Calculate blast

loading per section 6.3

of API 752

Yes

START

Explosion

Assessment

Complete

Is tent in Zone 3

(Figure 8)?

Owner/operator

criteria met? (5.2.1)

Change tent

design or siting or

otherwise mitigate

Yes

No

No

Yes

Assess tent’s blast performance:

Use blast load limits per Table 1

Perform structural analysis (6.3)

Rely on explosion testing (6.4)

Could tent be

impacted by

explosion? (6.1)

Apply measures to

reduce vulnerabilitiy (6.5)

No

Select tent designs

shown for Zone 3 in

Table 1

Apply tent occupancy limits for Zone 1

COMMITTEE DRAFT


6.2 Tent Siting Methodology

The tent siting methodology for explosion is practically identical to the methodology described in API RP-753. The

work process is as follows:

1. Calculate the congested volume of adjacent process areas and apply Figure 8 (Note Figure 8 is identical

to the zone curves in API RP-753). If the tent is located in Zone 3, then almost any type of tent is suitable

(see Table 1 for exceptions).

2. Tents located in Zone 1 or 2 require blast analysis to establish the blast overpressures and impulses at the

tent location. Table 1 provides options on the types of tents that may be used in Zone 2 given the blast load.

Some types of tents are suitable without structural analysis, whereas other types of tents require

demonstration that the tent meets the owner/operator’s acceptance criteria.

3. Tents located in Zone 1 may only house essential personnel.

Figure 8. Tent Siting/Design Guidance for Explosion Hazards

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Siting of tents other than those listed in Table 1 below should be evaluated on a case-by-case basis using a detailed

analysis (see §6.3).

Tent Type/Restrictions Located in Zone 1 Located in Zone 2 Located in Zone 3

Blast resistant tents

Note 1

Note 1 or Allowed if free field

pressure ≤0.9 psi and impulse ≤80 psi-ms

Allowed

Engineered tents with no sides, 90 mph wind rate

pole tents, or 90 mph light frame tents

Note 1 or Allowed if free field

pressure ≤0.9 psi and impulse ≤80 psi-ms

Allowed

Non-wind rated pole, light frame tents, tension

membrane tents, scaffolding tents or other

engineered tents

Note 1 or Allowed if free field pressure ≤0.6 psi

Allowed

Improvised tents and tents with rigid sides

Note 1 Allowed if reviewed and

approved by a competent

person

Tent occupant restrictions House only essential personnel

No restrictions No restrictions

Note 1: Allowed if the tent performance (via risk assessment, detailed structural analysis, and/or explosion testing)

meets owner/operator’s acceptance criteria (5.2.3)

Table 1: Tent Type/Restrictions vs Siting

The tent siting guidelines shown above are based on limited explosion test data [Reference 12] (API Tent Tests).

Generic blast capacities (e.g., pressure impulse curves) for tents have not been established by this RP because

there is limited test data, and too much variety in the choice of structural materials, connections, fabric, and

construction to specify a generic blast rating.

6.3 Detailed Structural Analysis

A detailed structural analysis uses appropriate dynamic analysis methods to assess the response of structural

components (skin or fabric, supporting ropes or framing members, posts or poles, tie-downs, etc.) to the potential

blast loads. As part of the detailed structural analysis process, structural response criteria for the components shall

be established. The criteria for metallic or wood components are discussed in various references [References 4, 5,

and 6]. The response of fabrics and ropes to blast is highly dependent on the specific materials used. For example,

the elongation prior to breaking of a nylon rope is significantly greater than that for a Dacron rope. Tent response

may vary depending on orientation to blast. EN 13782 [Reference 7] provides guidance on the analysis and design

of tents subjected to environmental loads. Annex A provides supplemental guidance to EN 13782 for the analysis

and design of tents subjected to blast loads.

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6.4 Explosion Testing

Testing may be used in lieu of or in addition to detailed structural analysis to establish the response of the tent to

blast loading. Both the overpressure and the impulse of the explosion should be representative of the blast load at

the tent location.

6.5 Measures to Reduce Occupant Vulnerability from Explosions

Explosion testing on tents and tent components have demonstrated that the tent structure and fabric can move

abruptly in response to the blast loads. Objects struck by the fabric could be thrown and become a debris hazard.

NFPA 5000 (Section 32.2.5.4) and many local building/fire codes that cover tents specify that the interior perimeter

(e.g., 3 ft width) be open/clear for egress purposes. Keeping the interior perimeter clear will also reduce the injury

potential from the tent’s response to a blast load. Personnel and unanchored objects should not be located within

3 feet from the interior edge of the tent facing the blast. See [Reference 12] (API Tent Tests) for more information.

Strong blast waves can topple or displace large ground level equipment (vending machines, tall shelves, food

preparation equipment, etc.). Such objects should be adequately secured to prevent tent occupant injury. Sudden

tent displacement in response to the blast may cause attached overhead items such as lights, and HVAC equipment

to fall. Overhead equipment should be secured or supported to prevent this injury potential.

Other measures which may reduce occupant vulnerability to explosion include:

Assembling and maintaining the tent in accordance with the applicable manufacturer’s recommendations,

and local building codes, if any. Particular attention should be paid to connections.

Evaluating and considering the location and the number of exits to provide appropriate emergency egress.

Providing egress and escape paths away from hazardous process areas where practical.

COMMITTEE DRAFT


7 Tent Siting Evaluation for Fire Tents included in the tent siting evaluation shall be sited and designed to meet the owner/operator’s tent siting

evaluation criteria for fire.

7.1 Work Process

Tent siting for fire hazards shall follow API RP-752 Section 7, with the following additional considerations:

1. The analysis may account for the reduced fire potential with process areas that are shut down and de-

inventoried of hazardous materials for the entire time the tent is occupied.

2. Tents are more vulnerable to fire exposure than permanent buildings and may have additional fire hazards.

Flame impingement and radiant heat may degrade or ignite, melt or soften the tent fabric materials and may

potentially release toxic fumes or drip hot material on personnel.

3. Occupants inside tents may be more vulnerable to flash fires from expanding burning vapor clouds than

occupants inside buildings.

4. Shelter-in-place is not a practical option for tents.

7.2 Egress and Evacuation for Fire

Evacuation for fire includes both egress from the tent and evacuation to a designated assembly area in accordance

with the owner/operator’s emergency response plan.

The assessment of safe egress from a tent included in the tent siting evaluation should consider the amount of time

available to evacuate, the number of occupants in the tent, the number of exits, and location of exits away from the

fire source. The tent may initially shield occupants from thermal radiation associated with external fires, allowing time

for tent egress and emergency response.

The assessment of safe evacuation should consider the evacuation route/distance, the fire thermal flux and duration,

and the total number of people involved in the evacuation.

8 Tent Siting Evaluation for Toxic Material Release Tents included in the tent siting evaluation (and included in the siting evaluation) shall be sited and designed to meet

the owner/operator’s tent siting evaluation criteria for toxic material release.

8.1 Work Process

Owners/operators shall determine if the tent included in the tent siting evaluation could be impacted by a toxic

material release. Where no potential toxic material release scenario is identified that could adversely affect the

occupants of the tent under consideration, a siting evaluation for toxic material release is not required; however, the

determination shall be documented.

Tent siting for toxic material release shall follow Section 8 of API RP-752 with the following additional considerations:

1. The analysis may account for the reduction in potential toxic material releases when process areas are shut

down and de-inventoried for the entire time the tent is occupied.

2. Tents typically have high gas infiltration rates but may be specifically designed to have low infiltration rates. In most cases, tents are not suitable for shelter-in-place. Specialized tents may be used for shelter-in-place.

COMMITTEE DRAFT


8.2 Egress and Evacuation for Toxic Material Release

Evacuation for toxic material release includes both egress from the tent and evacuation to a designated assembly

area in accordance with owner/operator’s emergency response plans.

The assessment of egress from a tent included in the tent siting evaluation should consider the amount of time

available to evacuate, the number of occupants in the tent, and the number of exits.

The assessment of evacuation should consider the evacuation route/distance and the total number of people

involved in the evacuation.

COMMITTEE DRAFT


Annex A

(Informative)

Structural Analysis for Tents and Other Soft Sided Structures

This method of analyses may be used to determine the appropriate location for a tent or other soft-sided structure in

the absence of test data, as discussed in §6.23.

Structural analyses of tents may be performed as prescribed in European Standard EN 13782-2005 [Reference 7]

but modified by the additions and exceptions described in this annex. Each sub-section heading in this annex

contains a reference to the pertinent paragraph number from the EN Standard. This annex describes how the

procedure prescribed in the corresponding paragraph of the EN Standard is modified to conduct a structural analysis

of a tent.

A.1 Wind Loads (Refer to EN Standard §6.4.2)

The local jurisdiction wind loads may be used in place of the wind loads identified in this section of the EN Standard.

If there are not wind loads specified for tents or soft sided structures by local jurisdictions, provisions EN Section

6.4.2 should be used.

A.2. Fundamental combinations (Refer to EN Standard §6.6.2)

The partial safety factor, F, is 1.0 for blast loads.

A.3 Blast Loads (Additional Section) (Refer to EN Standard §6.7)

The loading of a flexible structure such as a tent is more complex than for typical buildings in that the response of

the tent fabric may be fast enough to alter the applied pressures. Tents may allow the blast wave to propagate

through the fabric as well as leak through openings and reduce the net load on the tent. Structural analyses may be

performed to evaluate the response of the tent at its proposed location under three different loading cases: (1) Rigid

Body Loading, (2) Windward-Leeward Loading, and (3) Blast Transmission through the Tent.

Those three loading cases are intended to bound the actual loadings that may occur on the tent envelope and

frame. The time of application of the load for each panel of the structure should be based on the time required for

the blast wave to reach the midpoint of the panel. If dynamic fluid structure interaction calculations that account for

fabric movement or test are performed, the results of those calculations may be used in lieu of the prescribed load

cases. Test data that captures the reduced pressure may also be used in lieu of the loading cases below, provided

the test conditions are representative of the expected service conditions.

Case 1 – Rigid Body Loading

This case represents the loading that the sides and roof panels of the tent would receive if it were a typical building.

It does not account for air leakage or pressure loading transmitted through the tents. The reflected pressure and

impulses will be applied to the sides and roof panels facing the source of the blast. The appropriate reflection

factors that account for both the incident overpressure and the angle of incidence are available from the ASCE

[Reference 4] and other sources.

COMMITTEE DRAFT


The incident overpressure will be applied to the back of the structure and to the roof panels either facing away from

or parallel to the direction of the blast.

Figure A 1. Load Pattern for Case 1 Loading (Blast Source to the Left)

Pi = Incident Pressure

Pr = reflected pressure

Cr(α) = reflection coefficient (as a function of angle in degrees, α)

Case 2 – Windward-Leeward Loading

This case represents the load distribution that results from the blast wave loading the structure in a manner similar to

normal wind loads. The reflected pressure and impulses will be applied to the sides and roof panels facing the

source of the blast. The appropriate reflection factors that account for both the incident overpressure and the angle

of incidence are available from the ASCE [Reference 4] and other sources.

The incident overpressure will be applied to the back of the structure and to the roof panels either facing away from

or parallel to the direction of the blast, but as outward pressures to capture the effect of the blast wave moving

through the structure.


COMMITTEE DRAFT


Case 3 – Blast Transmission through the Tent

This case represents the loading that will result if the blast wave enters the tent and attempts to blow out the roof

and back (and side) walls. The reflected pressure and impulses will be applied to the sides facing the source of the

blast. The appropriate reflection factors that account for both the incident overpressure and the angle of incidence

are available from the ASCE [Reference 4] and other sources.

The incident overpressure will be applied to the back of the structure and to the roof panels, but as outward

pressures to capture the effect of the blast wave moving through the structure.


A.4 Membrane (Refer to EN Standard §7.5)

Tent fabrics will respond as flexible membranes. The dynamic analysis shall account for this membrane behavior.

Reactions at the edges of the fabrics are transmitted to the tent structure either through bearing, or via mechanical

connectors.

Membranes may be analyzed with Single-Degree-of-Freedom (assumes rigid supports) or by a method that

considers the flexibility of supports such as Two-Degree-of-Freedom or Finite Element Analysis.

A.5 Verification of load bearing capacity of technical textiles and their connections (Refer to EN Standard

§7.6)

Where dynamic test data is available, Dynamic Increase Factors (DIFs) may be used to increase the design

resistance computed in Equation 7 of the EN Standard.

A.6 Safety Margin, Safeguards (Refer to EN Standard §7.7)

The framing members and/or poles of the tent shall be designed to resist the loads resulting from the fabric reactions

for Load Cases 1, 2, and 3.

It is recommended that framing member response be limited to the medium level of response as defined in ASCE

[Reference 4]. Frame connectors shall be able to transfer the calculated reactions between components and remain

ductile.

COMMITTEE DRAFT


The safety factor against overturning, sliding, and lifting for blast loads is 1.0.

COMMITTEE DRAFT


Bibliography

The following documents are directly referenced in this RP.

[1] OSHA, Title 29 Code of Federal Regulations (CFR) Part 1910.119, Process Safety Management of Highly

Hazardous Chemicals

[2] Dow’s Fire & Explosion Index Hazard Classification Guide, Wiley-American Institute of Chemical Engineers

(AIChE)

[3] Imperial Chemical Industries, “The Mond Index,” ICI PLC, Explosion Hazards Section, Technical

Department, Winnington, UK, 1985

[4] Design of Blast Resistant Buildings in Petrochemical Facilities, American Society of Civil Engineers (ASCE)

[5] PIP STC01018, Process Industry Practice, Blast Resistant Building Design Criteria, 2006

[6] PDC Technical Report 06-08, Single Degree of Freedom Structural Response Limits for Antiterrorism

Design, U.S. Army Corps of Engineers Protective Design Center, October 2006

[7] Temporary Structures - Tents – Safety, BS EN 13782 12/23/05

[8] Life Safety Code, NFPA 101

[9] Standard for Grandstands, Folding and Telescopic Seating, Tents, and Membrane Structures, NFPA 102

[10] DOE Standard 1088-95

[11] NFPA 5000, Building Structure and Safety Code, 2012, National Fire Protection Association

[12] API Tent Tests, 2014

Further Reading—The following documents are not directly referenced in this RP but may provide a useful source of

information.

General—References Not Specific to Particular Subject Area

Guidelines for Postrelease Mitigation in the Chemical Process Industry, Center for Chemical Process Safety (CCPS)

Lees’ Loss Prevention in the Process Industries: Hazard Identification, Assessment and Control, Third Edition, 2004

Tent Siting Evaluation Process

M. H. Goose, “Location and design of occupied buildings at chemical plants—assessment step by step,” Hazards

XV, The Process, its Safety, and the Environment, Getting it Right, April 4 to 6, 2000, Manchester, (IChem E

Symposium Series No. 147, pp. 461 to 476)

Guidance for the Location and Design of Occupied Buildings on Chemical Manufacturing Sites, Chemical Industries

Association (CIA)

Guidelines for Evaluating Process Plant Buildings for External Explosions, Fires and Toxics, Second Edition, Center

for Chemical Process Safety (CCPS) (work in progress)

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Risk and Risk Criteria

“Approved methods and algorithms for DOD explosives siting,” Department of Defense Explosives Safety Board

Technical Paper No. 14, Alexandria, Virginia, November 2008

Guidelines for Developing Quantitative Safety Risk Tolerance Criteria, Center for Chemical Process Safety (CCPS),

2009

PGS 3: Guidelines for quantitative risk assessment, TNO (the “Purple Book”), formerly CPR 18 (3.5 MB PDF) IN

ENGLISH

PGS 4: Methods for determining and processing probabilities, TNO (the “Red Book”), formerly CPR 12E, (1.4 MB

PDF) IN ENGLISH

Guidelines for Chemical Process Quantitative Risk Analysis—Second Edition, Center for Chemical Process Safety

(CCPS), Wiley-American Institute of Chemical Engineers (AIChE), 1999

M. Moosemiller, “Avoiding Pitfalls in Assembling and Equipment Failure Rate Database for Risk Assessments,”

Journal of Hazardous Materials, 130 (2006) pp. 128 to 132

Spouge, J., “New Generic Leak Frequencies for Process Equipment”, Process Safety Progress, December 2005

Occupant Vulnerability

Methods for the Determination of Possible Damage to People and Objects Resulting from Releases of Hazardous

Materials, TNO “Green Book,” CPR 16E, The Hague, Netherlands, 1992

Fire and Explosion

PGS 2: Methods for the calculation of physical effects, due to releases of hazardous materials (liquids and gases),

TNO (the “Yellow book”), formerly CPR 14E (3.3 MB PDF)

Guidelines for Evaluating the Characteristics of Vapor Cloud Explosions, Flash Fires, and BLEVES, Center for

Chemical Process Safety (CCPS), Wiley-American Institute of Chemical Engineers (AIChE)

Harris and Wickens, Understanding Vapour Cloud Explosions—An Experimental Study, British Gas PLC,

Communication 1408, 1989

Causes and Effects of Fires and Explosions, FM Global Property Loss Prevention Data Sheet 7-0 ©2006.

Evaluating Vapor Cloud Explosions Using a Flame Acceleration Method, FM Global Property Loss Prevention Data

Sheets 7-42 ©2012

Baker, W. E., Cox, P. A., Westine, P. S., Kulesz, J. J., and Strehlow, R. A., Explosion Hazards and Evaluation,

Fundamental Studies in Engineering 5, Elsevier Scientific Publishing Company, 1983

Estimating the flammable mass of a vapor cloud, Center for Chemical Process Safety (CCPS), Wiley-American

Institute of Chemical Engineers (AIChE), New York, 1998

Guidelines for Consequence Analysis of Chemical Releases, Center for Chemical Process Safety (CCPS), Wiley-

American Institute of Chemical Engineers (AIChE), New York, Copyright 1999 (with errata sheet)

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“The Prediction of Blast and Fragment Loadings on Structures,” prepared for U. S. Department of Energy, by

Southwest Research Institute, under contract with Mason & Hanger, and Battelle Pantex, Report No. DOE/TIC

11268, July 1992

Structural Design and Analysis

Biggs, J. D., Introduction to Structural Dynamics, McGraw-Hill Publishing Company, New York, New York, 1964

ASCE 7-05, Minimum Design Loads for Buildings and Other Structures

Toxics

FEMA 453, Risk Management Series: Design Guidance for Shelters and Safe Rooms, Providing Protection to

People and Buildings against Terrorist Attacks, Federal Emergency Management Agency (FEMA), May 2006

AIHA, Emergency Response Planning Guidelines (ERPG)

Temporary Emergency Exposure Limits for Chemicals: Methods and Practice, U.S. Department of Energy

Washington, DC 20585

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