Some common fire scenarios on LNG carriers include engine room fires, cargo tank fires, and leaks leading to fires. It’s important to have proper safety measures in place, such as fire detection and suppression systems, trained emergency response teams, and regular drills to ensure the crew is prepared to handle any fire emergency.
- Summary of Documentation Review
- Guidance on Risk Analysis and Safety Implications of a Large Liquefied Natural Gas (LNG) Spill Over Water – Document No. 1
- Key results extracted
- Cloud fire experiments
- Pool fire experiments
- Overall summary of results of experiments – pool fire & vapour cloud studies
- Results of 40 m3 LNG spills on water – Document No. 2
- Consequence assessment methods for incidents involving releases from liquefied natural gas carriers – Document No. 4
- Consequences of LNG marine incidents – Document No. 5
- Consequence modelling of LNG marine incidents – Document No. 6
- Potential for BLEVE associated with marine LNG vessel fires – Document No. 7
- Input to modelling work of other members of the working group
- Large hydrocarbon fuel pool fires: physical characteristics and thermal emission variations with height – Document No. 9
- Large hydrocarbon fuel pool fires: physical characteristics and thermal emission variations with height – Document No. 11
- LNG properties & hazards – understanding LNG rapid phase transitions (RPT) – Document No. 12
- LNG pool fire simulations – Document No. 14
- LNG decisions making approaches compared – Document No. 13
- Thermal response of gas carriers to hydrocarbon fires – Document No. 15
- Maplin sands experiments 1980 – dispersion results from continuous releases of refrigerated liquid propane & LNG – Document No. 18
- Maplin sands experiments 1980 – dispersion & combustion behaviour of gas clouds resulting from large spillages of LNG & LPG on the sea – Document No. 19
- Results
- Results of documentation review
- Summary
The primary aim of this section is to:
1 Focus on the particular elements in the allotted task, while not neglecting to bring to the other working group members issues that the subgroup considered influential or related to these elements for their consideration.
2 compile any reservations they had on the input information both to:
- show they had considered these and possibly discounted them;
or
- they had prepared important reservations not discounted, if any, for consideration by the wider working group;
3 conclude – finally the subgroup concluded on the most representative scenario.
As was discussed during the first WG meeting, the Sandia report is widely taken as a seminal work on this subject. There are, however, other studies that were used that both reinforce the findings of the Sandia report or question its findings. This ensured that a considered analysis was made, as opposed to simply accepting the Sandia report without question, when it remains clear that there are concerns within the industry over some of its findings. These concerns revolve around quantification of the following points:
- Large fire scenarios are required to threaten significant parts of a cargo tanks;
- large fires may occur if an LNG tank is ruptured and LNG dispersed to the sea;
- the release rate determines both the size of the fire as well as the duration;
- collision damage causing tank ruptures of, e. g. 1 m2, will fuel very large fires (dia > 300 m) but will have short duration (typically less than 15 min) due to the emptying of the tanks;
- smaller releases can fuel fires of longer duration with the potential of threatening a large part of one side of the vessel;
- these fires will have a very large flame height and may affect large part of the tanks above the main deck;
- experimental data from large LNG fires on water does not exist and the effects of oxygen starvation and possible smoke screening are not known. A conservative approach would be to apply heat loads from large pool fires without smoke screening;
- such fires will burn as pool fires with radiant heat loads 150 kW/m2 and convective heat transfer from the combustion gases with temperatures 1 000-1 100 °C.
Studies and Documentation Reviewed | |||
---|---|---|---|
Document № | Title | Organisation | Date |
1 | Guidance on Risk Analysis and Safety Implications of a Large Liquefied Natural Gas (LNG) Spill Over Water | Sandia Report | 2004 |
2 | Results of 40 m3 LNG spills on water | Lawrence Livermore National Laboratory | (circa 1983) |
3 | Spill tests of LNG and Refrigerated Liquid propane on the sea, Maplin Sands, UK, 1980 | Shell Research Ltd. | 1980 |
4 | Consequence Assessment Methods for Incidents Involving Releases from Liquefied Natural Gas Carriers | ABS on behalf of FERC | May 13th 2004 |
5 | Consequences of LNG Marine Incidents | DNV – CCPS Conference Orlando | June 29-July 1 2004 |
6 | Consequence modelling of LNG Marine Incidents | DNV – Baik, Raghunathan, Witlox – American Society of Safety Engineers | March 18-22, 2005 |
7 | Potential for BLEVE Associated with Marine LNG Vessel Fires | DNV – Dr. Robin Pitblado | August 2006 |
8 | Model of Large Pool Fires | J. A. Fay – MIT | sept-05 |
9 | Large Hydrocarbon fuel pool fires: Physical characteristics and thermal emission variations with height | Phani K. Raj – Technology & Management Systems | 18th August 2006 |
10 | Spread of Large LNG pools on the sea | J. A. Fay – MIT | October 2006 |
11 | LNG Properties & Hazards – Understanding LNG Rapid Phase Transitions (RPT) | ioMosaic – G. Melhem,S. Saraf, H. Ozog | 2006 |
12 | Report on the Outline of Collision between Japanese tanker Yuyo Maru No. 10 & Liberia Freighter Pacific Ares | Maru No. 10 & Liberia Freighter Pacific Ares MSA – Japanese Government | March 1975 |
13 | LNG Decisions Making Approaches Compared | Dr. R. Piblado, Dr. J. Baik, V. Raghunathan – DNV | 2005 |
14 | FDS LNG pool fire simulations: a preliminary study on the application of FDS to study potential marine tanker accidents | J E S Venart – University of New Brunswick | 1st June 2006 |
15 | Thermal Response of Gas Carriers to Hydrocarbon Fires | DNV For Shell International Marine Ltd. | 26th November 1980 |
16 | Public Safety Consequences of a terrorist attack on a tanker carrying LNG need clarification | US Government Accountability Office | February 2007 |
17 | Department of Homeland security : LNG Tanker Security – Direct Testimony Dr. Phani K. Raj | Dr. Phani K. Raj – President – Technology & Management Systems, Inc. | |
18 | Maplin Sands experiments 1980 – Interpretations and modelling of Liquefied Gas Spills onto Sea | Shell Research B. V. & Shell Research Ltd. | 1980 (Pub 1983) |
19 | Maplin Sands experiments 1980 – Dispersion results fro continuous releases of refrigerated liquid propane & LNG | Shell Research B. V. & Shell Research Ltd. | 1980 (Pub 1984) |
20 | Maplin Sands experiments 1980 – Dispersion & combustion behaviour of gas clouds resulting from large spillages of LNG & LPG on the sea | Shell Research B. V. & Shell Research Ltd. | 1980 (Pub 1982) |
21 | Maplin Sands experiments 1980 – Dispersion results from continuous releases of refrigerated liquid propane | Shell Research B. V. & Shell Research Ltd. | 1980 (Pub 1982) |
22 | Review of published experimental results | Lloyd’s Register of Shipping | Last ref. 1992 |
Summary of Documentation Review
Listed below are the salient points extracted from the documents submitted or researched that were reviewed by the subgroup. These points were those the group considered relevant to the terms of reference of the WG.
Those papers not referenced were considered not to have input directly related to the remit of the subgroup or the full WG.
Guidance on Risk Analysis and Safety Implications of a Large Liquefied Natural Gas (LNG) Spill Over Water – Document No. 1
The Sandia report is a compilation of previous work carried out in the field of Environmental Impact of Liquefied Natural GasLNG spills. The report summarises the different work and then performs various analyses with the assumption of certain inputs from the different input sources.
The report draws a number of conclusions, some of which are directly related to matters being discussed in this WG and within the remit of the work assigned to sub-group ′A′.
Key results extracted
- LNG cargo tank hole sizes for most credible threats range from two to twelve square metres, expected sizes for intentional threats are nominally five square metres;
- the most significant impacts to public safety and property exist within approximately 500 m of a spill, due to thermal hazards from fires, with lower public health and safety impacts at distances beyond approximately 1 600 m;
- large, unignited LNG vapour releases are unlikely. If they do not ignite, vapour clouds could spread over distances greater than 1 600 m from a spill. For nominal accidental spills, the resulting hazard ranges could extend up to 1 700 m. For a nominal intentional spill, the hazard range could extend to 2 500 m. The actual hazard distances will depend on breach and spill size, site-specific conditions, and environmental conditions
- cascading damage (multiple cargo tank failures) due to brittle fracture from exposure to cryogenic liquid or fire- induced damage to foam insulation was considered. Such releases were evaluated and, while possible under certain conditions, are not likely to involve more than two or three cargo tanks for any single incident. Cascading events were analysed and are not expected to greatly increase (not more than 20 %-30 %) the overall fire size or hazard ranges noted above, but will increase the expected fire duration.
Cloud fire experiments
Table 1 provides an overview of existing LNG spill testing data.
Table 1. Largest Spill Volumes Tested to Date Giving Pool Radius and/or Distance to LFL | ||||
---|---|---|---|---|
Experiment | Spill Size (m3) | Spill Rate (m3/min) | Pool Radius (m) | Downwind Distance to LFL (m) (Max) |
ESSO | 0,8 – 10,8 | 9 – 17,5 | 7 – 14 | 400 |
U.S.C.G. | 3 – 5,5 | 1,2 – 6,6 | ~7,5 | Not measured |
Maplin Sands (dispersion tests) | 5 – 20 | 1,5 – 4 | ~10 | 190 ± 20 m |
Maplin Sands (combustion tests) | 10,35 | 4,7 | ~15 | Not measured |
Avocet (LLNL) | 4,2 – 4,52 | 4 | 6,82 – 7,22 | 220 |
Burro (LLNL) | 24 – 39 | 11,3 – 18,4 | ~5 | 420 |
Coyote (LLNL) | 8 – 28 | 14 – 19 | Not reported | 310 |
Falcon (LLNL) | 20,6 – 66,4 | 8,7 – 30,3 | Not reported | 380 |
Pool fire experiments
Liquid Pool Spreading
Table 2. Largest Spill Volumes Tested to Date Giving Pool Radius and Max. Flux Rate | |||
---|---|---|---|
Experiment | Volume Spilled (m3) | Pool Radius (m) | Mass Flux (kg/m2s) |
Boyle and Kneebone (Shell) | 0,02 – 0,85 Quiescent water surface (laboratory) | 1,97 – 3,63 | 0,024 – 0,195 Increased with amount spilled & amount of heavy hydrocarbons |
Burgess et al. | 0,0055 – 0,36 (pond) | 0,75 – 6,06 | 0,181 |
Feldbauer et al. (ESSO) | 8 – 10,8 (Matagorda Bay) | 7 – 14 | 0,195 |
Maplin Sands | 5 – 20 (300 m dyke around inlet) | ~10 | 0,085 |
Koopman et al. (Avocet LLNL) | 4,2 – 4,52 (pond) | 6,82 – 7,22 | Not reported |
Overall summary of results of experiments – pool fire & vapour cloud studies
LNG pool and vapour cloud fire experiments and their results are summarised in Table 3. A detailed description of these experiments is provided in the following sections.
Table 3. Large Scale LNG Fire Studies | ||||||||
---|---|---|---|---|---|---|---|---|
Study | Spill Terrain | Spill Vol. (m2) | Spill Rate (m3/min) | Pool DIA. (m) | Surface Emissive Power (kW/m2) | Burn Rate (10-4m/s) or kg/m2s | Flame Speed for Vapour Cloud Fires (m/s) | |
Pool Fire | Vapor Cloud Fire | |||||||
U.S.C.G. China Lake Tests | Water | 3 – 5,5 | 1,2 – 6,6 | 15 (max) | 220 ± 50 | 220 ± 30 | 4 – 11 (measured) (1,8 – 4,95) | 8 – 17 (relative to cloud) |
Maplin Sands | Water | 5 – 20 | 3,2 – 5,6 | 30 (effective) | 203 (avg) (178 – 248 range) | 174 (avg) (137 – 225 range) | 2,1 (calculated) (0,945) | 5,2 – 6,0 |
Coyote | Water | 14,6 – 28 | 13,5 – 7,1 | Not measured | Not measured | 150 – 340 | Not measured | 30 – 50 (near ignition sources – decayed rapidly with distance) |
Maplin Sands | Land | No report | NA | 20 | 153 (avg) 219 (max) | NA | 2,37 (measured) (0,106) | NA |
Montoir | Land | 238 | NA | 35 | 290 – 320 (avg narrow angle) 257 – 273 (avg wide angle) 350 (max) | NA | 3,1 (measured) (0,14) | NA |
Results of 40 m3 LNG spills on water – Document No. 2
- Size of Spill – 25 → 40 m3;
- outflow rate m3/minute – 10 → 20 m3;
- varying wind speed;
- 1 metre depth of water;
- 50 m diameter pool;
- visible plume length – 50 metres.
Not much input on specific values for heat flux, duration & distribution.
Consequence assessment methods for incidents involving releases from liquefied natural gas carriers – Document No. 4
- Volume of spill – 12 500 m3;
- duration – 33 mins;
- heat Flux – 265 kW/m2;
- flame Length (height) – (240 → 310 m);
- small size spills only as practical input.
Summary results for pool fire calcs: Larger Pool size gives shorter fire duration and higher flame length.
Table 4. Summary of Results for Example Pool Fire Calculations | ||
---|---|---|
Hole Diameter | 3,3 ft (1 m) | 16 ft (5 m) |
Initial Spill Rate | 11 700 lb/s (5 300 kg/s) | 290 000 lb/s (130 000 kg/s) |
Total Spill Duration | 33 min | 1,3 min |
Maximum Pool Radius | 240 ft (74 m) | 440 ft (130 m) |
Total Fire Duration | 33 min | 6,9 min |
Flame Length (Height) | 910 ft (280 m) | 1 400 ft (430 m) |
Flame Tilt at Maximum Radius | 35 deg | 31 deg |
Consequences of LNG marine incidents – Document No. 5
- Quote: The effect of increased boil-off over water, will be to put more fuel into the same air space as over land without any mechanism for entraining more air.
- This is likely to make the fire smokier and thus less luminous, with a greater fraction of the combustion energy going into heating the plume and less into thermal radiation.
- Overall, large pool fires have several areas of uncertainty.
- The large evaporating pool that is sustainable for dispersion is too thin to sustain combustion at the much higher rate of LNG consumption in a pool fire – LNG cannot flow from the source out to the periphery sufficiently quickly to replenish the material lost to combustion.
- Another uncertainty is associated with the degree of additional smoke associated with pool fires over water. The smaller diameter pool and the greater smoke generation would tend to reduce the thermal hazard range. This consequence area could benefit from large scale trials on water.
Table 5. Discharge Results – Various Holes Sizes and Locations | ||
---|---|---|
Discharge Case | Above Waterline Release | Below Waterline Release |
Hole Size (mm) | 250 750 1 500 | 250 750 1 500 |
Initial Rate (kg/s) | 226 2030 8 130 | 200 1 800 7 220 |
Duration (hr) † | 19 2,2 0,54 | 30+† 3+† 0,8+† |
Total Release (%) | 69 % | 100 % |
† Durations are based on the average flowrate from the hole. For underwater cases this is an estimate only as the duration becomes complicated to estimate when the LNG driving force equalizes water back pressure. |
Consequence modelling of LNG marine incidents – Document No. 6
- Hole size: 250 mm → 5 000 mm;
- discharge coefficient: 0,6 → 1,0;
- Burn Rate Range: 0,089 → 0,353 Kg/m2s;
- Pool Radius: 29 m → 253 m;
- SEP: 178 → 265 Kw/m2.
Potential for BLEVE associated with marine LNG vessel fires – Document No. 7
- A further protection is the limit on internal tank pressure to 0,28-0,30 barg. It will be shown later (in the paper) this is a major limitation on cargo flash and hence BLEVE potential;
- this requires further investigation if it transpires that the safety valves are unable to accommodate the anticipated pressure rise.
Input to modelling work of other members of the working group
These papers did not provide any specific input to the work of the subgroup but were considered of possible use as input to the work of other members of the WG.
- Model of Large Pool Fires – J. A. Fay – MIT (Paper 8);
- Spread of Large LNG pools on the sea – J. A. Fay – MIT (Paper 10).
Large hydrocarbon fuel pool fires: physical characteristics and thermal emission variations with height – Document No. 9
- Variation of SEP depending on height.
Statistics of Uncorrected NAR Data Apparent Surface Emissive Power (kW/m2) | ||
---|---|---|
Data from | Mean | Std. Dev |
Top of Fire | 44,8 | 44,0 |
Mid Height of Fire | 105,0 | 35,9 |
Bottom of Fire | 230,2 | 10,2 |
- It was considered that further work might be required to ascertain the height of the flame, as clearly SEP impingement on the tank cover depends on height;
- it was concluded that it might be necessary to commission work to further examine this.
Large hydrocarbon fuel pool fires: physical characteristics and thermal emission variations with height – Document No. 11
- Importance of pool size on SEP.
Comparison of model predicted Assured parameter values r = 17,17 for CH4; β = 0,06; km = 130 m2/kg; Emax = 325 kW/m2; Ta = 293 Kx SEP with experimental date | |||||||||
---|---|---|---|---|---|---|---|---|---|
Fire Diameter (m) | Surface on which LNG Boils | Froude Number (Fc) (×10-3) | Soot Mass Yield (y) Notarianni et al. [17] correlation for smoke yield.x (%) | Soot Concentration (C1)(kg/m3)(×10-4) | Fraction at Length of the «Clean Burning Zone» (Ψ) | Soot Transmissivity (τ1) (×10-2) | Mean SEP Over the Visible Fire Plume Height (Emax) | Remarks | |
Current Model Tests Result (kW/m2) | From Field kW/m2 | ||||||||
15 | Water | 9,606 | 12,7 | 3,328 | 0,196 | 66,4 | 172 | 185-224 | Raj, et al [8]. China Lake tests |
20 | Land | 8,319 | 13,0 | 3,419 | 0,180 | 57,12 | 183 | 140-180 | Mizner and Eyre [16] |
35 | Land | 6,288 | 13,7 | 3,595 | 0,150 | 35,7 | 177 | 175±30 | Malvos and Raj [14], Montoir tests |
100 | Land | 3,720 | 14,9 | 3,926 | 0,093 | 4,0 | 113 | – | Potential size of future pool fire tests |
300 | Water | 2,148 | 16,2 | 4,272 | 0,033 | 0,0028 | 90 | – | Estimated pool size due to 1/2 tank content spill (12 500 m3 LNG) from an LNG Assumed optical depth at bottom of LNG fire = 13,8 m.x ship |
LNG properties & hazards – understanding LNG rapid phase transitions (RPT) – Document No. 12
- Rapid phase transitions are more likely to occur in LNG mixtures containing very high fractions of ethane and propane. LNG composition is a critical parameter;
- the hazard potential of rapid phase transitions can be severe, but is highly localised within the spill area.
LNG pool fire simulations – Document No. 14
- The author had assumed that pressure valve settings were increased from 0,25 MARVS when at sea to 3 Bar;
- the author had not accounted for the presence of inert gas surrounding the tank;
- the author was not aware that pressure could be reduced by using gas boil-off in the propulsion and or steam dumping;
- the author had not looked at the options for forced vaporising to reduce pressure;
- the author was apparently not aware that Moss Tanks were design for emergency discharge under pressure;
- no account of the heat reducing effect of water deluge systems, required by the IGC Code, had been accounted for;
- the author had assumed that rate of the evaporation would be similar to the limited spill simulation Montoir Pool tests, where a small amount of LNG (pool) was ignited in a pit in the ground. We concluded that the heat influx would be less and so evaporation rate lower. However, in their calculation no consideration was given to the dispelling of oxygen due to a 600:1 ratio expansion and their modelling was of a fully mixed oxygen – methane cloud along one side of a vessel;
- the author had assumed that a similar scenario to that of a Spanish LNG road tanker, that spilt LNG which then ignited. The tank was heated to the point of rupture and resulted in a BLEVE.
LNG decisions making approaches compared – Document No. 13
Proposed Baseline Cases for Models Used in LNG Marine Assessments.
Validation scale:
- Use Burro 3, 7, 8, 9;
- Coyote 5, 6;
- and Maplin Sands 27, 29, 34, 35.
Run models for dispersion only.
Large Scale:
- Use an amalgam of current cases reported by many current LNG workers.
- Run these models for dispersion and pool fire results.
- Puncture case – leading to near instantaneous release of 500 m3 LNG.
- Maximum credible event case (accidental release) – 750 mm hole above waterline releasing all the cargo that can flow from the single largest tank.
- Maximum credible event case (terrorism) – 1 500 mm hole above waterline releasing all the cargo that can flow from the single largest tank.
- Maximum credible event case (jettison) – 10 000 m3/hr for 60 minutes.
- Worst case event (single tank) – 5 000 mm hole above waterline releasing all the cargo that can flow from the single largest tank.
Material | Pure liquid methane |
Weather | Cases should be run for D 5 m/s and F 2 m/s |
Surface roughness | Use 0,3 mm and 10 mm |
Relative Humidity | 70 % |
Temperature | 20 °C air and water |
LFL | Base an latest data from AIChE DIPPR = 4,4 % vol |
Outcomes:
- Source term – discharge rate duration and total amount, pool diameter and thickness (maximum and event average), boil-off rate (maximum and event average).
- Dispersion – distance to LFL.
- Fire – sustainable pool diameter for pool fire (maximum and event average), duration, and distance to thermal radiation predicted of 5 kW/m2.
- ABS 2004a and Pitblado et al 2004 list example areas of LNG uncertainties that will probably require large scale experimental trials to resolve;
- these will need to involve both the LNG vessel itself, its response to mechanical damages and to the physical consequences of large LNG spills onto water.
Thermal response of gas carriers to hydrocarbon fires – Document No. 15
- The principal contribution of this report was considered to be as a verification control;
- it closely follows some of the work objectives of the WG and, as such, may be compared against work carried out at the behest of the WG;
- an unknown mentioned previously is the effect of SEP based on height and location to any fire. This is proposed in the paper as:
In Summarising the Results of Diagrams 1-9, We have for Condition with no Wind: | |||
---|---|---|---|
Surface | Flux in kW/m2 | ||
Location on Deck | |||
Fire Side | Middle | Side Opposite Fire | |
Horizontal at deck level | 150 | 40-150 | 16-150 |
Vertical at deck level | 300 | 60-150 | 30-150 |
Horizontal at dome level | 35-150 | ||
Vertical at dome level | 120-200 |
Maplin sands experiments 1980 – dispersion results from continuous releases of refrigerated liquid propane & LNG – Document No. 18
- Measurements in this paper were taken from sensors mounted at a range of heights;
- wind speed and direction was identified in being critical as this affects the flame shape, direction, heat transfer, exposure of any adjacent structure etc.
- «Further analysis of the heat and water content of the plumes is necessary before heat transfer relations may be applied with confidence».
Maplin sands experiments 1980 – dispersion & combustion behaviour of gas clouds resulting from large spillages of LNG & LPG on the sea – Document No. 19
- A maximum scaled volume of 25 000 m3 was considered to be covered by tests using 20 m3;
- The two most prominent features of the dense gas spill are the gravity spreading of the gas («Slumping») and the inhibition of vertical mixing by the density gradients formed («stratification»).
- Table 6 – Combustion Trials at Maplin.
Table 6. Combustion Trials at Maplin | ||||
---|---|---|---|---|
Trial Number | Material and Spill Type | Volume (m3/min or m3) | Wind Speed Wind speeds given are those relevant during the combustion studies.x (m/s) | Comments |
17 | LNG Continuous | 2,8 | 8 | Flame failed |
27 | LNG Continuous | 3,7 | 6 | Cloud fire |
38 | LNG Continuous | 5,8 | 5 | Cloud fire |
39 | LNG Continuous | 4,7 | 4 | Cloud and pool fire |
22 | LNG Instantaneous | 12 | 5 | Cloud fire |
23 | LNG Instantaneous | 8,5 | 5 | Flame failed |
24 | LNG Instantaneous | 12 | 5 | Cloud fire |
49 | Propane Continuous | 2,1 | 6 | Cloud fire |
50 | Propane Continuous | 4,3 | 7 | Cloud and pool fire |
51 | Propane Continuous | 5,6 | 7 | Cloud and pool fire |
68 | Propane Instantaneous | 5-10 | 6 | Cloud fire |
Table 7. Surface Emissive Powers | ||
---|---|---|
Surface Emissive Power (kW/m2) | ||
Material | Cloud Fire | Pool Fire |
LNG | 173 ± 26 | 203 ± 31 |
Refrigerated liquid propane | 173 ± 20 | 43 ± 9 |
Results
Results of documentation review
The figures below should be considered as representative ballpark figures that were derived based on a summation of the overall review of available documentation.
Read also: Fire protection and Fire extinction on Liquefied Gas Carriers
There are undoubtedly contradictory values appearing in the work submitted for review, however those below were felt to provide a representation of the values proposed in the different works.
- Heat Flux:
- worst case direct flame impingement – 325 kW/m2 (at source of flame hottest part);
- this value is maximum at base of flame & reduces with height;
- applies to pool fire (not cloud fire).
- pool fire sizing v SEP;
Diameter | kW/m2 | |
Small Pool Fire | 35 m | 220 |
Large Pool Fire | 300 m | 90 |
- Fire duration:
- release of 12 500 m3 = 8,1 minutes;
- for 330 m (cloud fire) pool diameter ≈ 90 kW/m2.
- Fire height:
- not currently possible to define – not addressed by work to date;
- pool size 35 → 300 m diameter.
Note: 35 m is considered to be unrealistically low due to probable structural failure.
- impingement:
- pool fire – worst case – side;
- flame impingement.
- deck:
- cloud fire – 170 kW/m2;
- gives a lower flame height;
- cloud is advised to be max 10 m in height:
- BLEVE – Depends on a number of factors;
- further consideration of this should be undertaken after modelling.
Summary
The result of the document review was that considerable uncertainty exists over the height of any LNG fire resulting from an accidental or deliberate release on water.
The height of the fire has a direct impact on the fire impingement and heat flux to which an Special Requirements for LNG and LPG gas carriersLNG carrier would be subjected. The conclusion is that further definition of the flame height may only be achieved with appropriate modelling, for which the group would be in a position to provide a range of values for the different inputs required. It is only from such work or, alternatively, from full scale tests of larger LNG pool fires on water, that the consequential heat fluxes could then be derived.
The latter full scale tests would also perhaps confirm the shift in opinions over Surface Emissive Power, where current expert opinion is now in favour of incomplete combustion in an LNG pool fire on water, reducing the SEP as the size of any pool fire grows.
Further work by the subgroup is, therefore, pending completion of both modelling of an LNG pool fire on water (CFD and/or solid flame) for a range of values, and output from full scale testing of a large LNG pool fire on water. The latter is considered not to be the remit of this group but nonetheless is an important input for a conclusive output to the work of the WG.