Petroleum storage tank fire prevention

Petroleum Storage Tank Fire Prevention

Explosion and fire in petroleum storage tanks are rarely occurs but when they do occur, the loss to property and environment is significant. Also, it is very challenging to control it as they require considerable resources both in manpower and equipment in order to extinguish successfully. Therefore, prevention is the only solution to manage it.

Petroleum storage tank fire prevention

We must understand the causes of failure before start discussing the concept of fire prevention.

Causes of Petroleum storage tank fires

It has been observed that most of the fires caused by lightning strike during bad weather, oil spillage due to failure of level controls, material contact by nearby explosion, static charge due to failure of safe loading practices and sunken of floating roof due to rain water accumulation.

Cause of Petroleum storage tank fires

Other causes may be Internal frothing, over pressurization, Earthquake, Sabotage, ignition of vapour cloud, Heater malfunctioning, Ignition sources, fire in dyke, Military Rocket/ terror attack/ war, Pyrophoric/ Pyrolytic action,  improper bonding and fire during operator sampling, Use of Mobile, Static charge by improper firefighting foam application on roof spill, Smoking in vapour cloud area, etc.

Causes of oil spill on roof of floating roof tanks

In descending order, below are the probable causes of oil spill on the roof of floating roof tank.

1. Overfilling
2. Damaged roof
3. Roof drain failure
4. Gas or high vapor pressure product entered
5. Roof cracked near pontoon
6. Damaged seal
7. Overheat of product
8. Roof landed with some legs down
9. Heavy rain

In descending order, below are the probable causes of Sunken roof

1. Heavy rain
2. Leg failure
3. Overfill
4. Damaged roof
5. Damaged pontoon
6. Gas in line
7. Roof drain failure



Petroleum storage tank fire prevention

8. Product on roof

After understanding the causes of failure and potential/credible scenarios, now let’s discuss about the safety systems to prevent spills and fire incidences.

Storage tank Fire Prevention practices and systems

As we have already discussed about the most significant causes of fires under heading “Causes of Petroleum storage tank fires”, based on these causes, below are fire prevention measures;

Static electricity: by controlling flow velocity under limit, ensuring healthy bonding & Earthing.

Lightening: by ensuring healthy double earthing with two separate earth pits. Lightning arrester cab be installed for tanks form area but not on tank. (Still there is some dispute for this provision as lightning arrested prone to attract lightning and may increase the risk). (This issue will be discussed in another article separately.)

Internal frothing, /over pressure/ Overfilling: By monitoring tank fill/ discharge levels as a routine, Response to high- & low-level alarm, react to any alarm, etc

Earthquake: construction as per seismic zone.

Vapour cloud & ignition by vehicle movement: by NO ENTRY of vehicles in vapour cloud area, ensuring spark arrester in all vehicles, ensuring approved spark arrester of vehicles, routine check of Fire vehicles spark arrester, etc.

Heater malfunction: Healthyness of Heater can be ensured by schedule checking, providing extra safety factors, etc

Ignition sources: Eliminate all near-by ignition sources, ensure flameproof/intrinsically safe electrical equipment, etc as per hazardous area classification.

Explosion/ debris –spark nearby explosion: by maintaining safety distance as per norms.

Radiant heat: Adequate spacing between tanks.

Ground fire: by ensuring good housekeeping, Preventing bund fire, etc

Sunken of floating roof due to rain: by ensuring adequate capacity of roof drain, routine checking & cleaning of roof drain, etc

Use of Mobile: DO NOT USE mobile in Vapour cloud area.

Static charge by improper firefighting foam application on roof spill: do not apply foam (The natural degradation of foam cover may lead to an electrostatic ignition by foam & water sinking through hydrocarbon product) except If there is higher probability of ignition by non-removable sources such as Lightning storm. If the product involved has a high conductivity such as crude oil.

Application of foam on oil in such case is, If possible, use fixed pourers for gently application, Foam generated by Monitor or Hand line should be applied on the internal shell of tank before going on product, Always maintain foam blanket level.

Safety systems to prevent causes and minimizing consequences

Safe designing and safety instrumented system should be proved to nullify failure rate on demand. Safety instrument functions with SIL-2 rating should be provided for all emergency control systems. (actual SIL level must be based on PFD rate based on significance of area/location)

The breather valves must be properly designed to avoid over pressure during loading and to avoid vacuum during unloading. Install the wire mesh on the tank ventilation openings to restrict the impinging of flame.

Do not use air to mix oil.

Provides fire-resistant insulation for critical vessels, pipes, exhaust valves in tanks, valve actuators, instrument lines and major electrical installations.

Provide remote controlled, automatic and fire stop valves to stop loss of tank contents in an emergency; Protect these valves against fire. The valves must be coupled to the tank and must be resistant to corrosion or other harmful effects of spilled liquids.

Fixed roof tanks are constructed with a weekly weld connection in the connection between the roof and the housing to release over-pressure.

A peripheral railing and a walkway, if fixed at the top of the wall and outside the ceiling, make the wall-ceiling connection too strong compared to the resistance of the wall-ceiling connection. The result is that the over-pressure can cause the floor to dig and break away from the wall instead of tearing the roof.

For tanks fitted with internal heaters, an adequate level must be maintained on the surface of the heater in order not to overheat the contents of the tank and generate steam or reach the auto-ignition temperature.

High level alarms, the flow instrumentation alarm system and closures should be completely separated from the level and normal flow measurement with separate sensors and control units. The inherently safer design contains overflow pipes which are routed to a safe location and secondary containment. Level sensors that depend on the pressure difference to detect level changes should be avoided when changes in the specific gravity of the contents of the tank are expected.

Provide a safe method of removing water from tanks that store organic products and removing water from the tank roof.

Provide secondary containment around tanks to prevent spill from spreading to other areas.

The flood pipes must be dimensioned so that full flow is possible in the event of the tank overflowing. A general rule of thumb for estimating the size of the overflow pipe is that it should be at least one standard pipe size larger than the inlet pipe, but the exact size will depend on the pressure drop in the pipe.

Summary

With ref to petroleum storage tank fire incidents data, most of the fires caused by lightning strike during bad weather, oil spillage due to failure of level controls, material contact by nearby explosion, static charge due to failure of safe loading practices and sunken of floating roof due to rain water accumulation. Storage tank Firefighting s very challenging as they require considerable resources both in manpower and equipment in order to extinguish successfully. Therefore, Fire prevention is the only solution to manage it.

Release of contaminant can be prevented by providing safety instrumented system and good practices of deigning. Fire incidences can be prevented ensuring basic safe operational practices.

Related Article

Full surface storage tank firefighting strategies

You may find affiliate links in this article. This means that if you click on a link and purchase any of the products on this page, we may receive a commission, at no additional cost to you, It does not affect our knowledge sharing, opinions or reviews. Everything we do is benefit for you as the reader, so all our knowledge sharing, reviews are as honest and unbiased as possible.