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46 � FIRE & RESCUE � THIRD QUARTER 2010 Read our e-magazine at www.hemmingfire.com

LNG RESPONSE SERIES – PART THREE

gaps at the lower part of the pattern can allow cold vapourthrough the “wall”. It is only common sense not to placecomplete trust in any water wall or water curtain for preventingflammable vapour migration, and more so with LNG cold vapoursat the lower “wall” areas.

Use of foaming for LNG vapour control

Much is made of the need for foaming an unignited LNG spillwith high expansion foam to reduce vapour emissions andthereby reduce the risk of ignition through less vapour migrationto potential ignition sources – but only if it is in a contained trapor pit. The hazards of shifting wind direction, potential flash fireand potential contact with the cryo liquid tend not to rule infavour of a portable high expansion foam attack. If respondersfeel strongly enough that it can and should be part of theresponse, it is strongly recommended that it is extremely well pre-planned and the consequences fully understood and appreciatedbeforehand.

The author has attended and witnessed numerous tests whichclearly demonstrated that use of high expansion foam on a LNGfilled pit can reduce flammable vapour emissions downwind.However, we are then faced with how often to re-apply foam tomaintain this vapour reduction. This is an issue that applies tofoaming for fire control, which is discussed below, and on whichthere is currently little guidance to help the emergency responder.

Foaming for fire control

Foam is not as effective on LNG as it is on say, gasoline, naphthaor kerosene spill fires, because of the interface between thewarm foam and the cryogenic LNG creating increasingvapourisation which then breaks through the foam. One of thereasons for minimising the surface areas of spill catchment pits isto optimise the depth of the high expansion foam blanket, sothere is an effective barrier against heat reflected back into theLNG pool and the general insulating effect on the pool is aseffective as possible.

It has been said that if there is a high enough application rate,any flammable liquid fire can be extinguished with firefightingfoam. The author cannot subscribe to this theory where LNG isconcerned. This is because low and medium expansion foamscontain too much water (between 97-99%) which obviouslywarms the liquid and thereby increases the vapourisation process,which in turn intensifies the burning process. (Conversely, lowand medium foams are of course easier to apply from a firedepartment viewpoint.)

It is also because application of high expansion foam into a pitneeds good freeboard – or space – to fill above the spilled liquidlevel; is also affected by rainfall; and lastly because highexpansion foam is very susceptible to wind losses.

The reality is that only high expansion foam can provide aneffective vapour reduction (unignited contained spills) or radiantheat reduction (burning contained spills).

Portable application of high expansion foam is not advised forLNG pit fires, since it means close approach to set-up, and timedelays for foam application. The temperatures involved in an LNGfire, especially a high Methane content LNG fire, can reach1,300oC. The radiant heat levels from such a fire mean thatresponders trying to move portable pourers into the pit edge can

Use of water spray for LNG incidents

Water spray is useful for protection from radiant heat but it shouldnot be considered for direct flame engulfment, which impliesliquid in depth, due to the water contacting the liquid and therebyincreasing the rate of vapourisation, which in turn, increases theintensity and radiant heat levels from such a fire.

Water for LNG vapour migration control may be useful andeffective for contained spills, but if this water enters the LNG itself,there will be immediate warming of the liquid which in turn leadsto higher rates of vapourisation – basically, the incident will beescalated through greater vapour cloud migration distances.

While use of water wall or water curtains to minimise vapourmigration can be effective for contained spills, responders need tobe aware there are two weak links in this line of defence.Typically, water spray, water wall or water curtain nozzles carriedby fire departments will have gaps at the interface between theground and the lowest part of the spray curtain/wall. It is herethat cold vapours may pass through to the other side of thecurtain. In addition, if the curtains are not overlapping there will begaps at the sides.

Much will depend on the type and design of water wall orwater curtain in use, but it must be remembered that cold LNGvapours will be heavier than air initially and will therefore migrateat low levels. While water patterns will heat these vapours andcause the vapour to rise (since it is mainly Methane), if thecurtain is not “solid” at the sides vapour can get through and the

Attacking the LNGIn this the final part of our LNG response series

author John Frame provides practical advice on

extinguishing media usage, and recommends that

industry issue a definitive set of fire and control test

results for LNG. An impossible dream, perhaps?

An example of drychemical monitors

in action. Notevisibility levels andwind effects. LNG

ships may alsohave dry chemical

systems for theircargo manifold

area.

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only approach under water spray protection – yet this water mayfind its way into the pit and thereby increase fire intensity.

High expansion pourers must be over the pit edge to beeffective. In addition, hardened stainless steel pourers canwithstand LNG fire effects and should have preference over lightalloy material. Most portable high expansion foam pourers arealloy and will not resist such a fire for more than a few minutes.

If there is adequate land space, pit locations may be such thatradiant heat emissions are harmless and therefore a burn-outstrategy can be achieved safely. The reality is that land is always ata premium and therefore the majority of pits will have a fixedhigh expansion foam system fitted.

By the way...

As an interesting aside, we work in an industry where – at least inthe fire response field - companies do not talk to each other. AsLNG becomes more commercially lucrative, more companies arefocusing on LNG as part of their futurebusiness strategy and will be carrying outtheir own tests to determine hazards andconsequences, usually resulting in a differentset of foam application rates!

In fact, considerable fire testing and foamapplication test work has already been done.For instance in the 1960s the USA Bureau ofMines tested at Lake Charles, Louisiana, withTokyo Gas also testing in Japan around thesame time. In the 1970s further test workwas carried out by Philadelphia Gas Works,then the American Gas Association in theUSA, then British Gas in the UK. As LNGbecame more commercially viable other oiland gas companies appeared and in the1980s, and Shell’s research centre inThornton began testing in the UK.

Gaz de France followed with tests atMontoir-de-Bretagne, France, followed byboth them and Shell joint testing in the1990s – it’s no secret that most of thecurrent knowledge of rapid phase transitionsstems from Gaz de France’s fire testing work.The latest company to run tests was BPbetween 2004 and 2006 (although it ispossible others are now underway).

A sad part of all this is that we cannot, asan industry, get together and issue definitivefire and fire control test results to which allagree. Different test criteria, different LNGgrades, different burn times and differenthigh expansion foam rates and applied foamapplication rates have ensued and althoughthese can no doubt be defended by thedifferent groups involved, it would make lifesimpler if we had a single, universal set ofrates to think about – an impossible dreamperhaps, since although close, there aredifferences in existing low and mediumexpansion foam application rates betweencountries.

Having said that, given the scenariosinvolved, it is not really envisaged that anemergency responder will be setting upportable high expansion pourers when aserious incident occurs in LNG terminals or,indeed, in liquefaction plants. The vagaries of

weather conditions, wind speed and high radiant heat levelsmean that portable high expansion application is highly unlikelyand is not recommended.

Foam application duration

The question of foaming, for either vapour reduction or radiantheat reduction, needs to consider for how long the vapour willcontinue to be produced or, if ignited, the fire will continue toburn. Applying a single foam application to either an unignitedspill or a fire will not work due to breakdown of the highexpansion foam blanket. It needs to be re-applied fairly regularly ifit is to be effective in maintaining the required vapour reductionor radiant heat reduction figure.

Some ad hoc work was done on this a few years ago but theoutcomes and results were not at all well defined. If there hasbeen some recent guidance produced then it is most welcomeand readers are invited to share and contribute accordingly. Some

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standards mention reapplication three times as part of their testregime, but no more than this. The challenge is therefore toestablish guidance for responders that will allow them to re-applyfoam for effective vapour or fire reduction at frequent intervalswhere the depth of liquid is known, as in (say) a containment pitwith a defined level.

Adhering to a fire protection standard that, perhaps, calls for a15-minute application time for a flammable liquid spill fire doesnot consider the duration of application over time to maintain firereduction to a given radiant heat level.

If there is a two-metre depth of LNG and the burn off rate is12.5mm/minute, the fire will burn for around two hours and 40minutes. A single high expansion foam application of someminutes will not resist the burning LNG for too long. If there areno further applications possible, the fire will simply return to itsmaximum size as the foam breaks down and burns off. In manyinstances, this question of re-application is not fully addressed.

One practical aspect to determine whether re-application isneeded will be to play water streams over those exposures thatmay be close to the pit. Again, if it steams, the radiant heat levelsare not being reduced and foam needs to be re-applied.However, this will only happen if there are enough appropriatefoam concentrate reserves.

It will be a great service to emergency responders if guidanceon re-application of foam can be provided – and preferablyuniversally.

A final and important point for responders is that for pits whichare level with the ground and where high expansion foam hasbeen applied – for vapour control – the edges of the pit will behidden by the depth and spread of foam applied. Personnelshould not attempt close approach for vapour monitoring as theymay fall into the pit!

Extinguishment using dry chemical

LNG fires can be extinguished by using dry chemical, provided, ofcourse, that there is enough dry chemical; it is applied correctly;and the subsequent vapourisation or vapour cloud, post-extinguishment, will not create a greater hazard.

Containment pits

For smaller surface area pits eg up to 15m2, portable 12kg drychemical extinguishers may be used safely and effectively, in pairs.Beyond this size, large wheeled extinguishers are advised, from75kg up to 125kg for greater coverage, for each pit and always aminimum of two for each pit. Note that standards may call formore than the above, dependent on country of location.

Tank relief valve vents

Single walled tanks may still be in use in some locations but themore modern plants and terminals will have double-walled tanks,referred to as “full containment tanks”. These have an inner 9%nickel steel tank and an outer tank of pre-stressed concrete. Thetanks are operated at atmospheric pressure.

In some cases, the tops of LNG storage tanks may have drychemical systems fitted at the tank safety valves, should thesevalves lift and release vapour which is then ignited. Given thedifficulties of hauling extinguishers up to the tank top, and riskconsiderations of moving and working on tank tops, this isobviously an advantage for responders – provided, of course, thatthe system maintenance is effective.

The principal reason for the dry chemical system at the vents isbecause of the previously mentioned rollover hazard. The reliefvalves will be found at the top of the tank on a valve platform atone end. It should be noted that such tanks can be >25 metreshigh, which is quite a vertical climb carrying portable extinguishers,should risk assessment consider such a deployment.

Jetties dry chemical systems

Some LNG terminals berths/jetties may have tower-mounted drychemical monitors, specifically for the loading/discharge manifoldarea, where there is higher potential for releases. One of thedrawbacks of using large quantities of dry chemical is that visibilitymay be greatly reduced and in some cases, the user of thesystem may assume extinguishment when in fact the flamecontinues unseen.

Trailer or skid mounted dry chemical monitors may also beconsidered on some sites. Although definitely useful in trainedhands, again, the visibility issue must be considered. It ispreferable to have a “spotter” at right angle to the streamapplication to indicate stream direction in much the same way asusing a large capacity foam cannon on an oil storage tank fire.

Ship cargo operations response

LNG ships have a number of protection systems, including a driftlimiting envelope which, if exceeded, will actuate an emergencyshutdown. This can include automatic closure and disconnectionof the loading/unloading arms. The connection is known as PowerEmergency Release Couplers (PERCs), either automatically ormanually actuated.

Ships usually load and unload with a water spray running underand around the potential spill area at the manifold. This willvapourise minor spills and prevent contact with the ship’s deck ofcarbon steel. Cracks in decking have occurred through contactwith LNG. Stainless steel containment is also used under themanifold and over decking for catching minor spills and directingoverboard.

There should be a catchment pit in case of a serious liquidrelease from the loading arms and pipes and this may be atdolphins or end of jetty or other area away from the loadingmanifold arms. The spill routing is sometimes interesting but solong as the liquid ends up in the pit, the routing channels will not

Trailer or skidmounted dry

chemical monitorsmay also be

considered onsome sites.

Although definitelyuseful in trained

hands, again, thevisibility issue

must beconsidered. It is

preferable to havea “spotter” at right

angle to thestream applicationto indicate streamdirection in muchthe same way as

using a largecapacity foam

cannon on an oilstorage tank fire.

46-50 LNG[1]rev.qxd 11/8/10 12:28 Page 48



normally present a residual fire hazard.The spill containment pit for thie jetty pictured above is

at left centre. The braced stainless steel ducting on thelower right of the pit is used as the flow “bridge”. Notethe close proximity of the ship to the pit, which isunavoidable and the reason why high expansion foam isprovided for the pit

LNG ships also have the following fire protectionsystems:

• Water spray for fire prevention, cooling and personnelprotection, which covers:

•• Exposed cargo domes•• Deck storage tanks for flammable products•• Cargo lines and control valves

• Boundaries of accommodation blocks, compressorand pump rooms, cargo control rooms and storerooms containing flammable materials that face thecargo area;

• Fixed dry chemical for firefighting in the exposedmanifold cargo area with at least two hoses ormonitors capable of reaching the manifold area.

Summation

LNG is probably the cleanest of the fossil fuels, and infairness is now probably the safest fossil fuel (incomparison to others) that is produced, transported bysea, stored in terminals for vapourising and distribution toindustry and housing. The hazards thus far are fairlyclearly defined and obvious and in the main are protectedagainst, both in terms of preventative, containment andreactive measures.

In closing, the author hopes that the relatively saferecord of LNG continues for the lifetime of this fuel’savailability, and that responders are faced with no morethan minor incidents.

However, responders should always know what toexpect when an emergency is declared at LNG facilitiesand it is hoped that the above information will providesome guidance for this. Just as importantly, respondersshould also know that there is a time to intervene, and atime to stand off. This, of course, is a matter for pre-planning and not waiting for the event before decidingwhat actions to take.

All responders are encouraged, always, to be proactiveand discuss scenarios and response actions according totheir respective sites and facilities.

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The spillcontainment pit is

at left centre.Note the close

proximity of theship to the pit,

which isunavoidable andthe reason whyhigh expansion

foam is providedfor the pit.

Article authorJohn Frame hasnot only created

and deliveredLNG fire response

training coursesbut he also

produced theoriginal book

“LNG FireProtection &EmergencyResponse”,

available fromIChemE.

46-50 LNG[1]rev.qxd 11/8/10 12:29 Page 50

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