1. LPG/LNG - Fire Behaviour and Control
H P Singh
Dy. General Manager (S&EP)
Indian Oil
National Work-shop on Challenges of Fire Risks in
New Millennium
August, 2000
New Delhi

2. Energy Consumption
Per capita Energy Consumption in Metric Tonnes of Oil Equivalent
World 1.5
India 0.3
USA 6.3
Europe 3.1
China 0.7

3. Supply/Demand of Petroleum Products
YEAR Petroleum Natural
Products Gas
(MMT) (MMSCMD)
15 MMTPA LNG import by 2007

4. LPG/LNG Clean Fuel Use of LPG in transport sector permitted
Stricter emission norms will enhance use of LPG/LNG
Growth rate of Petroleum Sector is around 6%.
LPG demand is expected to increase by 15%.
Natural Gas growth rate is expected to be 11%.

5. Natural Gas Domestic supply of Natural Gas is almost stagnant
Demand has to be met by large scale import
Import route
- Pipeline
- LNG (1/600 times volume reduction)
Considering the present political scenario and energy security imperatives, LNG is the only route available atleast in medium term

6. LPG/LNG Success in use of LPG/LNG depends on Safety and Reliability in
Storage, Transportation and handling

7. Hazardous Properties of LPG
Mixture of Propane & Butane
Colourless & Odourless : difficult to identify
Vapour Pressure : kg/cm2 (max.) at 65 0C
: about 9 kg/cm2 at 38 0C
Boiling Point : C - readily vapourises on leakage
Vapour density : 2.5 kg/m3 (Air 1.29 kg/m3)
Heaviour than air, so vapour cloud settle in the ground level and travel considerable distance

8. Hazardous Properties of LPG
Flash Point : C
Explosive range in air
Lower 1.9 % by Vol.
Upper 9.5 % by Vol.
Auto-ignition Temperature : C
LPG vapour is always much above flash point so highly hazardous.

9. Hazardous Properties of LNG
Contains mainly Methane. Typical composition is as under:
(% Vol)
Methane :
Ethane : 3 - 5
Propane :
Butane :
Pentane :
Nitrogen :

10. Hazardous Properties of LNG
Colourless & Odourless : difficult to identify
Boiling Point : C - readily vapourises on leakage
Molecular wt. of LNG is 17.5 and is much lighter than air.
Liquid Density : 450 kg/m3
Since vapour is lighter than air, it diffuses quickly. LNG is stored at (-) C. At low temperature, LNG vapour is heavier than ambient air and hence can form vapour cloud. This cloud duration will not be high.

11. Hazardous Properties of LPG
Explosive range in air
Lower % by Vol.
Upper % by Vol.
Auto-ignition Temperature : C
LNG (Methane) is a flammable gas in ambient condition and hence highly hazardous.

12. Hazardous Properties of LPG/LNG
Gas to liquid volume ratio :
LPG : 250
LNG : 600
Volume of flammable mixture per unit volume of liquid:
LPG : 12000
LNG : 10800

13. Fire Behaviour
Fire is a rapid self sustaining oxidation process accompanied by evolution of heat and light of varying intensity.
Supply of fuel, oxygen and heat in right proportion along with uninhibited combustion chain reaction is essential for fire to continue.
Fire Fighting is actually the process of breaking up the combustion chain reaction.

15. Explosion Generally fuel and oxygen is premix (Vapour cloud)
Combustion reaction is very fast. Rate is not delayed for bringing fuel and oxygen together.
Rapid increase in pressure characteristic.
LPG/LNG quickly transform into gas on release and as such can explode.

16. BLEVE Boiling Liquid Expanding Vapour Explosion
Major container failure
Container contains liquid at a temperature above its boiling point
Container fails due to excessive pressure :
Liquid full
Temperature of the liquid increases and no relief valve
Un-wetted portion of the shell gets heated up and metal loses its strength. Vessel ruptures with disasterous effect. Fire ball results.

17. LPG Vapour
LPG Liquid

18. BLEVE Relatively less number of fragments are generated
Fragments fly as missile by the energy released by the expanding gas. Speed of these fragments are very high and cause extensive damage to life and property.
60% of the expanding energy of LPG is converted to kinetic energy. Maximum initial velocity is
- Horton Sphere : 200 m/sec
- Bullet : m/sec
In case of LPG, distance reached by fragments are as under:
- Horton Sphere : 600 M
- Bullet : M
Fragment from one BLEVE can initiate a BLEVE in the nearby second vessel.

19. UVCE Unconfined Vapour Cloud Explosion
Release of flammable vapour in atmosphere
Mixing with air
Totally within flammable range or the outer layer is within flammable range
Delayed ignition
Flash Fire of UVCE depending on quantity and mixing with air
High pressure lasts only fraction of a second. Persons are not killed due to blast.
Secondary effects cause death and destruction.

20. UVCE Over Pressure Likely Damage (Bar) o.3 Heavy (90 % houses destroy)
0.1 Repairable (10 % houses damage)
Damage of glass
Crack of windows

21. LPG : Incidents BLEVE OF LPG Cylinder
1983 in Sakurbasti LPG Bottling Plant.
LPG Cylinder body valve leaks. Vapour cloud forms.
Contractor labour attempts to light ‘beedi’.

22. LPG : Incidents BLEVE OF LPG Bulk Tank Truck
, near Bhusaval. LPG TT overturn.
Liquid/vapour line got damaged and LPG started leaking
Impingement of LPG jet to metallic surface of the vessel.
Static electricity acted as source of ignition.
BLEVE of LPG TT.
Loud sound upto 3 KM. Vessel fragments into 4 parts. One piece traveled upto 350M.
Truck driver alerted the local people and stopped traffic on the National Highway. Hence, no casualty.

23. LPG : Incidents BLEVE OF LPG Bulk Tank Truck
, near Godhra (Gujarat). LPG TT head on collision with other truck (soyabean husk) at 0445 hrs.
LPG leakage from safety valve. Fuel tank of TT damaged and HSD spill on the road.
A matador hits the liquid/vapour line. LPG started leaking. Vapour cloud forms.
Probably somebody in the matador lights match-stick for light. Result is ignition of vapour cloud. Fire in the safety valve which impinges on the top surface like a jet.
BLEVE of LPG TT.
Vessel fragments into 3 parts. One dished end traveled upto 80 M.
7 persons died.

24. LPG : Incidents BLEVE in LPG Storage Facility
, Sun Juan, Mexico City. PEMEX lPG storage and distribution facility.
Series of explosions and fires.
500 killed injured of which 144 died in hospital homeless.
Facility consists 6 Horton Spheres, 48 Bullets m3 LPG at the time of the incident.
One pipeline (8”) from refinery leaks. Vapour cloud is formed which moves 100 M and reaches a ground flare.
Explosion took place. Recorded in the seismograph of Mexico City University (30 KM away).
Flame impingement caused rupture of spheres/bullets. Result is BLEVE.

25. LPG : Incidents BLEVE in LPG Storage Facility
Only 4 bullets remained on support.
2 HS did not explode but collapsed through buckling of their legs.
One fragment traveled upto 1200 M.
Houses were completely destroyed upto 300 M.
Some of the shortcomings observed:
Fire Water capacity - inadequate
Fire Pump-House within 50 M of the LPG storage
Spheres and Bullets nor provided with Water Spray
Supports were not fire-proofed
Spheres and Bullets were spaced very closely.
Settlement were very close to the facility.

26. LPG : Incidents Fire/explosion in LPG Storage Facility of a Refinery
, AM, LPG storage facility of an Indian refinery.
Fire/explosion took place.
60 persons killed. 27 storage tanks and 15 buildings including Fire Station and process control room destroyed LPG storage area damaged.
LPG was being unloaded from a tanker. Line-fill water was displaced into a Hortonsphere.
Problems experienced during water draining. LPG comes out from the sphere through the water drain line.
Vapour cloud forms. It was detected by Operating personnel.

27. LPG : Incidents
Small fire in a process unit occurred at that time. Either this fire or Canteen acted as a source of ignition.
Massive explosion and subsequent fire took place.
Major lesson learnt :
Water draining of LPG vessel is an extremely hazardous activity. Competent operating person must be present during water draining.

29. LNG : Incidents
Cleveland Ohio, USA. LNG storage tank ruptures. LNG vapour ignites and intense fire result. Liquid LNG flows through Storm water sewer and explode.
128 killed injured. Facility closed down.
Esat Ohio Gas Company liquefy Natural Gas during low demand and store which is gassified and supplied during peak period.
Metallurgy of the vessel (low carbon steel) was unsuitable. Vibration or seismic shock might have developed crack.
Major lesson learnt :
Provision of dyke is essential for LNG storage..

30. LNG : Incidents
Cove Point, USA. Explotion occurred in electrical substation of an LNG facility.
1 operator killed and 1 injured. Extensive damage to the substation..
LNG leaked through an inadequately tightened LNG pump electrical penetration seal, vapourised, passed through 200 ft of underground electrical conduit and entered the substation.
Normal arcing in the substation caused explosion.
Major lesson learnt :
Gas detectors to be provided to all buildings of LNG facility..

31. LPG/LNG : Types of fires
LPG leakage
Small - evaporate (heat from ground and surrounding air)
Large - evaporation and accumulation of liquid on ground
Immediate ignition
Pool Fire
Jet Fire
BLEVE
Heat Flux Damage Effect
(kw/m2)
5.0 Skin burns in 30 seconds
12.6 Minimum for ignition of wood
31.5 Destruction of metal structures
Heat flux of jet fire is very high ( kw/m2). Can cause extensive damage to pipelines, vessels and equipment.

32. LPG/LNG : Types of fires
Delayed ignition
Released liquid evaporate and disperse.
Dispersion depends on density of gas and meteorological conditions (wind speed & temperature)
LPG vapour is heavier and tend to spread in radial direction due to gravity. Gas pool with certain height and diameter results. At a distance from the gas pool, dispersion takes place according to atmospheric stability and equilibrium is reached. So the area in which concentration within the explosive limits does not extend far outside the edge of the gas pool.
On ignition, vapour cloud burns very quickly. Anybody inside the cloud burnt to death. Duration is short. No major thermal damage. Damage is primarily caused by pressure wave.

34. LPG/LNG : Types of fires
Some special features of LNG:
Small leak will immediate vapourise.
In case of large spillage, rapid vapourisation takes place for seconds. Then vapourisation takes place near the boiling point of Methane ( C). At this temperature, Methane is heavier than ambient air.
In case of immediate ignition, momentary flash fire occur. There is no over pressure. In case of delayed ignition, initial burning rate is very high, then the heat incident on liquid generates enough vapour to sustain burning and steady-state is achieved. There is no blast over pressure.
Fire fighting operation shall not add hot fire fighting agent to the liquid pool.

36. LPG/LNG : Types of fires
LNG burns with a clear flamme but LPG flames are smoky.
Smoke shrouds flame from target and reduces emissive power of flame surface.
- LNG : kw/m2
- LPG : 20 kw/m2
Smoke may appear in LNG fire only when pool diameter is large and most of the fuel has been consumed so that proportion of higher hydrocarbons are increasing rapidly.

37. Fire control & mitigation measures
HALON
Halon is excellent fire fighting agent for gas fires bit cannot be used due to environmental considerations.
DCP
Dry Chemical Powder (DCP) is very effective for small fires. Large fires cannot be extinguished as application will be difficult.
Even small fire should not be extinguished fully, if fuel cannot be completely isolated. Vapour cloud is more dangerous than small fire.
Potassium-bi-carbonate based powders are more effective than Sodium-bi-carbonate based powders.

38. Fire control & mitigation measures
FOAM
Good quality, high expansion foam (1:500) reduces intensity of fire greatly.
Foam alone cannot extinguish the fire as LPG/LNG fires generate enough heat to generate sufficient vapour to sustain combustion at the foam surface.
Foam aids vapourisation of LNG. Heating effect of foam is detrimental.
Foam generation facility has to be near the fire.
Foam cannot flow more than 50 M.
Depending on the situation, foam can be used on LNG fire. It will quickly freeze at the interface. Fire intensity reduces to a great extent. Remaining fire can be extinguished with DCP.

39. Fire control & mitigation measures
WATER
High specific heat and cheaply available in large quantity. Effectively used for cooling and radiation exposure protection.
Medium velocity water spray systems shall be provided in the storage and handling facility for exposure protection. It has to be automatic.
High speed, high volume water spray is effective for dispersion of vapour cloud. Water droplet heats the vapour and natural buoyancy helps dispersion.
Water shall not be applied to ignited or unignited LPG/LNG liquid.

40. Fire control & mitigation measures
Some special features of LNG:
Since vapourisation reduces automatically to a great extent after few seconds, zone of flammable mixture is limited. So dyke must be provided to restrict spill area.
Burning characteristic and radiant heat output of LNG pool fire is almost similar to gasoline fire. LNG burning rate is no more than gasoline on weight basis.
Once fire fighting operation starts, it shall extinguish the fire totally in one go otherwise the fire fighting agent will reach the liquid pool and generate more vapour.
Since autoignition temperature is high, chance of reignition is low.

41. Fire control & mitigation measures
Formation of vapour cloud is a dangerous occurrence. If size is large, probability of finding an ignition source is near certain. Ignition source is so varied, it will be practically impossible to exclude all source particularly in industrial situation. All care should be taken to prevent loss of containment.
While designing facilities, following OISD codes may be referred:
OISD-STD-144 : LPG Bottling Plant Operations
OISD-RP : Storage and Handling of Bulk LPG
OISD-STD-163 : Process Control Room Safety
OISD-STD-194 : Storage and Handling of LNG

42. Fire control & mitigation measures
Some of the important measures to be adopted are as under:
Automatic Water Spray System.
Fire proofing of supports of LPG vessels. LPG vessels may be fire proofed so that more time is available to arrange for evacuation and taking preventive measures.
New LPG facilities shall be mounded type so that chance of BLEVE is negligible.
Remote Operated Valve (ROV) for isolation.
Blast resistant type control room.

43. Fire control & mitigation measures
Do’s
Evacuate all persons form vapour cloud.
Approach fire from up wind only.
Activate ROV to isolate storage.
Start water spray system for nearby facilities also.
Keep portable DCP extinguisher near LPG/LNG handling facilities.
Water draining from LPG pressurised storage must be done by competent person.
Don’ts
Do not allow naked flamme, smoking, welding/cutting etc. near LPG/LNG facility
Do not extinguish the fire completely unless fuel can be isolated.

44. Thank You