Pre-fire plan and emergency response for LPG sphere fire in oil refinery
Tags: Safety, Emergency Response, Refinery, Fire, Lpg

The pre-fire plan and emergency response strategy are crucial at oil refineries, petrochemical and oil & Gas terminals to mitigate any gas leak, fire and explosion emergency. The pre-fire plan helps emergency responders to manage any emergency efficiently by identifying the proactive mitigation actions for each credible identified emergency scenario and thus helps to minimize the losses.

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The storage of Liquefied Petroleum Gas (LPG) possess high risk of fire and explosion due to its flammability property and may form vapour cloud at ground level due to its high density.

In this article, we will discuss the different credible emergency scenarios in handling and storage of LPG and action plan to mitigate these emergencies by improving the implementation and practice of the pre-fire plan (PFP) or the pre-incident plan (PIP). We start with the general handling and storage process of LPG, associated hazards, Fire protection system,emergency response planning and firefighting strategies.

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LPG is mixture of propane and butane and is stored in bulk quantity at refinery and gas terminals, mostly stored in pressurised vessels and Horton spheres from where it is transferred to LPG gantry for wagon filling. Mounded vessels are also used for storing the LPG in some installations. In some refinery, LPG is directly transported to market through fixed pipeline from storage facility.

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Below are the major hazards of LPG bulk storage

· Explosion -UVCE and BLEVE and secondary fires

Three main factors responsible for BLEVE, one is the over pressurization due to the boiling of liquid, the second vaporization rate is more than venting and the third is material loose it’s tensile strain due to prolong heating by an external flame.

These three factors resulted in a catastrophic rupture of container and the pressurized flammable vapour released suddenly in the form of massive explosion called BLEVE.

A secondary fire in nearby facility can be caused by shock wave and propelled pieces of container.

UVCE occurred when flammable gas released into the atmosphere, after some delay, forms a vapour cloud and ignited by ignition source away from its point of leak source resulted into deflagration.

In UVCE, the flame propagate at an ultrasonic velocity thus produces shock waves and destroys the entire installation covered under the cloud.

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A secondary fire in the facility can be caused by shock wave and direct contact of fire and explosion.

If the gas is heavier than air (LPG, vapours of gasoline, diesel, kerosene and other hydrocarbons), the flammable cloud covers more area whereas lighter gas (hydrogen, methane, etc) forms less flammable cloud because it disperses easily.

LPG Horton spheres or vessels are placed into groups and each group is limited to six spheres/vessels.

Storage quantity of each group is limited to 15000 M3 and curb wall provided around the storage area for containment of leakage. Storage spheres/ vessels are installed in single row and vessels/ bullets must not be stacked one above the other All storage spheres/ vessels are separated from each other in same group or from adjacent group by minimum distance of 30 meters. Minimum 30 meter separation distance maintained form group to group also.

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In case of LPG vessel, installation should be such that the longitudinal axes of horizontal vessels or bullets must not be pointed toward any other process facility, equipment or other LPG storage container.

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The height of curb wall around the LPG storage tank is limited to minimum 30cm and maximum 60 cm.

Safe separation distance of LPG bulk storage should be maintained during designing stage and it must not be less than 60 meters from process units, control building and any electrical substations.

Separation distance from flare, fire stations and process unit heater/ furnace must not be less than 90 meters whereas it should not be less than 30 meters from nearest oil storage area, loading gantries and rail spurs.

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· BLEVE due to the prolonged heating by flame impingement to storage tank shell and secondary fires.

Entire LPG storage facility is provided with fire water ring main with fire water hydrants and water monitors. Fire water header pressure is mostly maintained at 10.5 kg/cm2 at all time. Automatic water spray deluge system is provided for all LPG storage spheres/ vessel covering compressors/ pumps and important isolation valves. Flow rate of water spray system is 10.2 lpm/m2 for storage tank and 20.4 lpm/m2 for compressor and pumps.

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Here in this article we are discussing the emergency response plan for the LPG Horton sphere

Now we are discussing here the common course of actions for all types of LPG emergencies by each key member .

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Depending on the situation, site incident controller will guide the operating team to initiate the necessary isolation or the emergency shutdown of facility, if necessary. Site incident controller must ensure that all of the above emergency actions have been taken by the operations team.

The site incident controller will take all relevant information from the fire commander and decide on the strategy to follow in consultation with Fire chief for additional resources, calling for mutual aid and adopting alternative methods to mitigate the emergency.

The site incident controller must ensure that the area is barricaded, that the movement of vehicles is restricted, that evacuation and enumeration at the assembly point are done by security team.

The site incident controller must request the maintenance team to perform a maintenance activity to stop the leak in accordance with their standard operating procedures.

He must ensure that the injured person has been transferred to the health center and also ensure the availability of first aiders and auxiliary firefighters.

The site incident controller must initiate an adequate level of emergency siren after discussion with the chief incident controller (Refinery Head).

He is responsible for declaring “All Clear” after ensuring the safe mitigation of the emergency. Before declaring “All Clear”, he must assess the situation for damage and the environment.

The maintenance leader must ensure that the maintenance team immediately reaches the incident site with the necessary non-sparking tools and resources in accordance with their standard operating procedures and initiates the action line in accordance with safe maintenance practices.

Maintenance in charge must report to the site incident controller and issue directives for the continuation of the maintenance activities to be carried out.

The security officer must report to the incident site immediately after receiving an emergency call and report to the site incident controller.

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The pre-fire plan or pre-incident plan is prepared to effectively mitigate any emergency to minimize the losses. Generally, thepre-fire plan is developed by emergency responders such as fire and rescue services. NFPA 1620 provides detailed guidelines for developingpre-fire plans to assist emergency responders in effectively mitigating emergencies. When developing thepre-fire plan, it is necessary to ensure the protection of plant peoples, emergency response personnel, property and the environment.

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Ref. Quantitative Risk Assessment (QRA) of the LPG storage spheres , t he risk

The pre-fire plan can be prepared by the fire department in consultation with the operations team. Pre-fire plan should be prepared for all credible scenarios. Here for understanding, we are considering below major scenarios having maximum impacts.

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Vapour cloud explosion and risk of BLEVE due to LPG leakage from downstream flange of LPG spheres body valve at Storage, Sales, Dispatch Area (SSDA)”

Leakage of LPG in liquid phase from downstream flange of MOV due to Gasket failure (Considered — Sphere body valve is not in position to be closed manually & ROV not working)

Vapour cloud has formed and covered about 1 km area.

UCVCE occurred due to unknown source.

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Fire at flange with jet flame impingement on the adjacent LPG sphere.

Prolong Flange impingement on Sphere shows sign of BLEVE

Three LPG spheres present in one group of layout

Wind speed is about 24 km/hr

Diameter of LPG Sphere = 17m.

LPG is received from storage area and stored in SSDA LPG sphere and dispatched to LPG gantry for wagon filling.

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Material Name : LPG

Operating Temperature : 25 deg C

Operating Pressure : 8 to 9 kg/cm2

LEL : 1.9 %

UEL : 9.5 %

TLV : Butane : 800 ppm Propane : 1000 ppm

Normal Boiling Point : -40 deg C

Auto-ignition Temperature : 432 deg C

Vapour Density : 1.5–1.8 gm/cc

Specific Gravity : 0.51–0.58

Water Solubility : Slight, 6.1% by volume

BLEVE: — If the fire not controlled & insufficient cooling operation may lead to BLEVE

Damage Distance (685 m) @ 37.5 kW/m²

Damage Distance (1180 m) @ 12.5 kW/m²

Damage Distance (1978 m) @ 4.0 kW/m²

Explosion shock waves can damage the Life & property within 2 KM range.

Adjacent LPG spheres (3 No) may cause s[Read More]

It is desirable that the leaks cannot be controlled after extinguishing fire and wherever the leak can be controlled, attempt to extinguish the fire.

Fire water requirement for affected sphere cooling = 556 m3/hr

Fire water requirement for adjacent two sphere cooling = 1112 m3/hr

Fire water requirement for hose stream and one monitor = 375 m3/hr

Fire water requirement for fixed ground water monitor (4Nos) = 912 m3/hr

Total fire water Requirement = 2955 m3/hr

SCBA set = 14 Nos with 100% spare cylinders

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Portable gas monitor = 3 Nos

Transportation for manpower replacement = 2 Nos

Dehydration remedy kits = 4 per person

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Report to site and take charge of incident site as per Emergency management and response plan.

Assess the site & coordinate with DCS panel officer for mitigation.

Direct all emergency operations as per SOP.

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At end of an emergency, assess damage & environmental / toxicity level, declare ALL CLEAR.

After receiving an emergency call, the fire team must present themselves urgently with all appropriate firefighting equipment, personal protective equipment and report to the emergency site.

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While taking emergency turnout from the fire station, make sure of the wind direction, be in constant contact with the fire control room. After reaching the emergency site, the fire tender / fire engines should only be parked in the upwind / crosswind direction. The fire tender must be parked in a safe place and directed towards the exit.

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Operate the groundwater monitor / tower monitor and HVLRM ( high-volume long-range monitor ) for water.

Help the operations and maintenance team to mitigate the incident. If there is a demand to close the process isolation valve which is engulf in fire, the responder must wear a fire entry suit with a water spray back-up line. These water spray must continue to provide a cooling effect to the personnel involved in closing the isolation valve.

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After ALL CLEAR, stop the operation of fire protection system and communicate the fire water pump house about no further demand. Ensure the restoration of all emergency fire equipment / appliances.

Reach at Site & report to CIC.

Controls access to the Incident site

Allow smooth entry of external emergency team as per ERMP and through predicated entry gate.

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Fire Brigade — entry shall be as per ERMP

District Authority: — Arrange for extra resources and evacuate nearby community

Emergency No of fire control room: XXXXXXXX

DHDT panel contact No: XXXXXXXX

Above is the one example of pre-fire plan for LPG storage sphere fire for specific scenario. Similarly, pre-fire plan must be prepared separately for each credible scenario with ref to QRA study.

Standard template for Pre-fire plan for oil Refinery credible scenarios

Sample pre-fire plan for LPG sphere emergency

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