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FAST AND EFFECTIVE RESPONSE TO LNG VAPOUR RELEASES AND FIRES Kevin Westwood Group Fire Advisor BP United Kingdom www.bp.com Mike Willson Angus Fire United Kingdom www.angusfire.co.uk
ABSTRACT BP are leading the world in practical test work to define modern approaches to LNG fire protection and vapour dispersion. Working with partner Texas A&M university and leading manufacturers, like Angus Fire, in fire suppression and detection technology, they have developed a world class LNG test facility in Texas. Intended to promote an overall understanding of LNG safety issues and how to deal with them. The paper will cover some of the practical LNG testing, training and research work that has defined optimised high expansion foam application rates for LNG fires and vapour releases, proven the effectiveness of leading LNG Turbex foam generating systems and other equipment for detecting and controlling LNG. It has also dispelled some of the historical misunderstandings surrounding control of LNG releases.
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Introduction LNG is playing an increasingly important role in helping meet growing world demand for energy and cleaner fuels. Against this background, the Texas Engineering Extension Service (TEEX), a member of the internationally respected Texas A&M University system, BP, Angus Fire and other Industry equipment and supply partners have developed the world’s foremost hands-on LNG fire training and equipment testing facility at Brayton Field, College Station, Texas.. Open to Industry this facility has received worldwide recognition for providing the opportunity to develop practical skills and knowledge of how best to handle LNG incidents in modern LNG liquefaction, storage and vaporisation plants as well as during loading and unloading operations, shipping and road transportation. To date, training of personnel who may be faced with an LNG release has taken place at fire facilities and has mainly been carried out involving pits constructed in wide open spaces. What makes this new facility unique is that it is purpose built and has full detection, suppression and infrastructure facilities available. This provides realistic LNG vapour release and fire scenarios for demonstration and hands on emergency response training.
The LNG fireground at Texas A&M featuring three containment pits with a combined area of over 410m2, L shaped two level trench and marine manifold The facilities are also being utilised for practical LNG research and testing and are contributing to the accumulation of a body of knowledge that can be shared with all those involved in the Industry. To date more than 150 first responders from existing and proposed LNG facilities across the world have completed the intensive three day course offered by the facility. Such training is leading to a better understanding of facility layout and operations and additional ways to enhance the safe handling of LNG. This paper will highlight how the facility has helped the further development and testing of fast and effective responses to potential LNG vapour releases and fires.
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The Facility Test installations are of most value when they reflect actual plant. It is also important that state-of-the-art equipment requires to be engineered specially to withstand the rigours of LNG hazards and can be proven in LNG fires, not just under standard test conditions, but also under more extreme scenarios. The design and construction of the containment pits and trench which have been provided at TEEX to collect the run off from LNG spillage, have therefore been based on those already existing at real LNG terminals. Three different size concrete steel reinforced pits have been constructed to simulate various design layouts including one with extended vertical walls above ground. In most facilities, any LNG spill would be collected via channels that would run from areas around the plant this having been determined as the most probable location for any accidental release of a spill/release occurring. At the TEEX LNG facility, an open L shaped trench is provided, complete with steel pipes in the lower section, two levels below grade construction, to simulate service pipework, which some existing facilities carry along their spill channels. The configuration of the containment pits and trenches allows that multiple variations of small and large spill vapour release and fires can be produced, which to date have been from 3,000 to 35,000 gallons(US) (or 11 to 132 m3). The information collected from these initial three years of training and test fires, shows that containment pit design impacts on the behaviour of the larger LNG vapour cloud and radiated heat from LNG fires. All this information is currently being fed into the BP sponsored PhD programme at the Texas A&M University’s Mary O’Connor Process Safety Center. Current Standards The Texas A&M pits have been purpose built to simulate current vertical sided, reinforced concrete impounding basins in use around the world. Foam for LNG Facilities A major activity undertaken at the Facility has been the testing of equipment and application methods for the best use of foam. The current fire protection standards such as NFPA 11:2005 provide guidance and state that “discharge rates per unit area shall be established by test” and “final design rates are generally 3-5 times test rates”. It also recognises that “special attention should be given to heat effects since time to initiate actuation is a critical factor in LNG fire control”. NFPA 59A does not currently recognise the value of foam for vapour control and dispersion or controlling the fire and suppression of the radiated heat following ignition of the vapours. Rapidly draining foams will increase LNG vaporisation rates and exaggerate fire intensity, so foam and equipment should therefore be proven by test on LNG, before selection for use in operational facilities.
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Foam can be of major assistance in controlling LNG releases in impounding basins or spill pits, loading manifold sumps and spill trenches. Foam provides increased safety in an emergency by reducing the vaporisation rate and dispersing the vapours directly upwards, away from ignition sources, thereby minimising the risk of vapour cloud ignition. If ignition should occur, foam quickly provides high levels of fire control and rapid heat radiation reduction, thereby protecting personnel and exposed equipment. It is a valuable protection for a controlled burn-off of the LNG spill and minimises the risk of escalation. Throughout the training and testing programme at the TEEX facility, all ratios of foam production were utilised from low expansion at 7:1 through to high expansion at 500:1 to determine what worked and what did not.. The programme also conducted a number of trials with CAFS (Compressed Air Foam) that showed practical difficulty and limited effectiveness on small 10m2 pit fires. These established that a quality high expansion foam of 500:1 expansion is most effective but that other foams are too wet, with the result that heat transfer from water to the LNG can cause the product to vaporise faster, increasing fire intensity without being able to provide adequate control and radiation reduction. Vapour Dispersion Technologies The Facility has been used to analyse the dispersion of vapour arising from LNG. Several technologies have been looked at: water fan spray; high expansion foam; gas imaging technology and open path gas detection.
A Hydroshield 180° water fan spray The Angus Hydroshield 180º water fan spray unit has been tested to show containment of gas clouds in the facility although care must be taken to avoid run-off water entering the LNG pit.
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To reduce vapourisation, a well formed 500:1 high expansion foam cover is necessary. This can reduce vaporisation by 60% over the course of 2 minutes of foam application. The foam also warms the reduced vapours so they rise vertically away from potential ignition sources which are more likely to occur at ground level.
High Expansion foam reducing and dispersal of LNG Vapour Foam was also observed to lock LNG beneath it, as was found when a hole broken through the ice found new vapour rising above the 5% LEL limit. State-of the-art thermal imaging cameras show the effectiveness of the foam blanket when images are superimposed, to confirm a 60% vapour reduction with this high expansion foam application. The latest gas imaging technology has been brought to the Facility for evaluation and development. Remarkable progress has been made with this cutting edge technology as the images shown demonstrate. Of particular interest is the ability to ‘see’ the differences in the flammable methane vapour being held and diverted by water sprays and water monitors as against the vapours going through the water screens which can be identified as non-flammable because of lower concentration. The experiments at the Facility have already resulted in commercially available remote methane leak detection cameras incorporating lessons learned at TEEX, being demonstrated in September 2006. Following many tests of various gas detection techniques, the Facility has the most up to date infra-red gas and vapour technology, giving coverage around the entire LNG fireground. Infra-red open path, or line of sight gas detectors are linked back to a central processor on the edge of the Facility, so that attendees can obtain a first hand understanding of detector operation, field of view, LEL alarm settings and the optimum configuration for any given vapour release scenario. Together with hand-held portable detectors to supplement the fixed systems, this fully operational, state-of-the-art gas detection system gives the maximum possible flexibility to students, researchers and design specialists to determine the most efficient application for gas/vapour detection at both current and future LNG facilities. PS7-1.5
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Open path infra–red fixed gas detection Fire Control Technologies The ability to test and understand LNG fires has been enhanced at the Facility by the installation of closed circuit miniaturised television cameras in flameproof housings, strobe lights and alarms all linked to a microprocessor in the support building. Such ground-breaking technology allows an LNG fire to be recognised in seconds and a real time visual image to appear on a controller’s desk or remote console anywhere in the world. Originally developed for the offshore oil industry to counter false alarms from reflected flare radiation, this detection camera technology has found the ideal application at the Facility. Over three years of developing the fireground, much refinement of the digital signal micro-processing and software algorithms has been made, to cater for the very particular visible range of an LNG flame. Using both stand-alone units and multiple detectors it is possible to monitor the entire fireground for any ignition, however small or large, by processing the live image and interpreting flame characteristics, discriminating between genuine fire conditions and other radiant sources.
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Miniaturised CCTV flame detection Testing at the Facility under realistic conditions has confirmed previous work in the area of fire control. In the specific area of high expansion foam, different application rates of EXPANDOL foam at 500:1 have enabled recommendations to be developed of what will work in dynamic situations with less than ideal conditions, such as wind and rain impacting on the release, which need to be considered in practical facilities.
Schematic showing how High Expansion foam works to control LNG fires The figure above illustrates how foam can insulate and reduce radiation feedback to the LNG, allowing a safe and effective controlled burn-off. Pit design can assist or hinder this process. After an initial foam application, the heat from burning vapours above the foam can cause it to break down. By pulsing the foam on and off, it is possible to keep good control with the pit full of foam. These regular top-ups maintain a steady state and reduce radiation by up to 90%. The skeletal 500:1 frozen foam layer that floats on the LNG also helps to control the fire intensity. Extinction of an LNG fire using high performance dry chemical powders such as MONNEX may be an option on small or medium-size fires, but this is far easier to achieve above a high performance 500:1 foam blanket.
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The benefit of this powder is that it can break up as it hits the heat of the fire, enabling quicker and effective “mop-up” of free radicals. This can help to stop the event early, before the fire gets out of control. This was observed at TEEX on fires within the containment pits. This splitting up of MONNEX in the flames helps to compensate for poor application technique; all students attending the BP LNG Workshops are given 1 to 1 instruction so that they are trained in the benefits and limitations of using dry chemical on various sizes of LNG fire. In practice, physical obstructions, lower quality powders, or the extent of the fire may inhibit extinction. Hence, technique is still a critical factor in achieving success.
Chemical Dry Powder being used by students under direction from senior TEEX instructors It is important to note that attempting extinction may not always be the best answer, because of the potential for flashbacks or re-ignition. In this case, the best option is usually a controlled LNG vapour burn-off through a high quality 500:1 high expansion foam blanket, as it reduces the radiant heat, providing a safer environment and preventing damage to surrounding plant. Fixed Foam Generators The units tested were Angus Fire LNG Turbex high expansion foam generators, delivering 500:1 expansion ratios and specially rated to be capable of withstanding the cold and heat of an LNG spill and possible ignition, where high temperatures are likely to be achieved. A 316 stainless steel boiler-grade body with 316 stainless steel aerofoil fan blades avoids distortion and can ensure reliable air flow and foam expansion are achieved.
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An LNG Turbex Foam generators under test High temperature bearings and insulation around the water turbine and special lubricants are essential to prevent seizure and binding of the fan on the casing which otherwise could halt operation. Robust discharge hoods are required to direct the foam into the pit and minimise the impact of wind, without reducing the expansion ratio or stability of the foam being produced. It is important that enough good quality foam lands in the pit to achieve the levels of control required. Angus Fire’s Engineering Division is now using results from the tests, together with proven Angus Fire products, as the benchmark for any LNG fire protection systems. Effective Radiation Reduction Tests run between 2004 to 2006 at the Facility have demonstrated the effectiveness of foam application rates in reducing radiated heat. This is illustrated in the following graph, which is based on tests at the 65m2 pit. This shows the Radiometer reduction measured 30m away from the pit in a cross wind direction. 2
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Figure showing a 90% radiation reduction in under 60 secs
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In these specific LNG Turbex tests, application rates of 500:1 high expansion foam at 10litres/m2/min have been shown to provide fast control and reduced radiation emissions by 90% within 60 seconds with fast pit filling. Quality 500:1 high expansion foams will produce an effective finished foam blanket with fresh and salt water.
The fire area before and after Expandol High Expansion foam application This comparison from radiometer readings shows that heat outputs drop fast when the right foam and equipment combination is applied, e.g. from around 7.5kW/m² to 0.7kW/m² within 60 seconds of foam application when LNG Turbex and EXPANDOL high expansion (500:1) foam is applied, measured at 30 metres away in the cross-wind direction on the upwind side. These findings show the benefits of installing the most efficient and effective detection and protection technology. Ensuring that any spill, leak, or escape of LNG is immediately detected either as a vapour or if ignited, allows the operators to utilise fixed foam systems to maximum positive effect in containing vapour release and/or reducing heat radiation and quickly controlling the fire. Ongoing Testing and Research Whilst the LNG Industry can be justifiably proud of its safety record, the TEEX facility continues both with advanced LNG fire training and practical ongoing research to improve further the speed and effectiveness of response to potential LNG incidents. Combination fire hydrants, mobile 5 inch pumper connections, oscillating fire monitors, and passive fire protection with the latest materials are continually being tested against radiated heat and flame impingement. Equally, experience from terminals and liquefaction plants are continually fed back into the development of the Facility. The latest tests carried out in October 2006 utilised Pittsburgh Corning Foamglass inherently fire resisting blocks pre-positioned within the small 10m2 containment pit. The Foamglass cellular glass block was cut into small cubes of 3.5 x 3.5 cms {1.5 x 1.5 inches); shrink-wrapped and sealed in UV and weather resistant polyethylene bags. The bags are designed to float to the surface of the LNG should there be a leak or spill. If ignited, the polyethylene bags are intended to burn off, releasing the cubes of cellular glass to form a barrier and thereby aid in the suppression of the fire. LNG was then poured over the “bagged” blocks in a simulated spill scenario. The test was undertaken to see if the blocks would reduce vapourisation and radiated heat, both of which would aid suppression by dry chemical extinguishers.
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The tests indicate a significant reduction in the radiated heat when the vapours were ignited, the flame being easily extinguished with dry powder. However no visible minimization or vapour control effects were witnessed and additional testing is required to determine the effect if any on vapour volume reduction. Conclusion The existence of the TEEX Facility is allowing the LNG Industry to further test and develop methods for the fast and effective response to vapour releases and fires. Tests to date highlight the effectiveness and benefits of rapid gas detection using open path systems, visual CCTV flame detection and high expansion foam systems, to provide effective fast vapour dispersion and fire control capabilities necessary in modern LNG facilities. All organisations and companies involved throughout the LNG chain of liquefaction, shipping, re-gasification and gas transportation can experience this unique facility for the benefit of the LNG community worldwide. To date the facility, expertise, research and equipment donated have enhanced the understanding of a wide range of design houses, constructors, project engineers, regulators and operators who have attended and gained experience of LNG releases, vapour cloud control, LNG ignition and fire control to the benefit of them personally, their organisations and the whole LNG industry. BP and TEEX has provided an enduring facility for the whole LNG industry to use and many further workshops are planned to maintain this momentum and LNG’s safe reputation.
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