At the outset, we would like to state that we are not experts on explosions but are writing to contribute to providing an understanding of the fires that ensue from explosions and the measures to be taken to control the ensuing fires.
Explosions are the en uncontrolled release of energy leading to shocking impacts of immense momentary pressure exerted on the surroundings.
Generally, accidental explosions happen due to negligence in taking adequate measures in hazard areas, handling of processes without proper knowledge, lack of periodic safety audits covering inspections, mock drills of safety systems and poor preventive maintenance programmes.
The results are potentially high damages to property and lives which can be beyond recovery and restoration to normalcy.
How explosions are associated with fires:
Explosions are generally followed by an outbreak of fire. In some cases, the outbreak of fire followed by the explosion can prove to be of more destructive than the basic extent and cause of the explosion itself.
Therefore, any safeguard planning used to control explosion has to be extended to take care of the subsequent spread of fire also.
For example A small explosion due to unprotected storage of firecrackers can result in accidental charging of all stored firecrackers resulting in shattering of doors, windows, control panel, in spillage of flammable alcohol, edible oil, sparking in electrical switches and appliances due to sudden shock. Therefore, where ever potential hazards exist for an explosion, the safety measures outlined in the in the respective country should be followed. From the perspective of fire safety, the use of active and passive fire measures can reduce the impact of the ensuing fire from an explosion.
On the other hand, a fire can instigate an explosion. To avoid any such situation, fire protection to the safest feasible levels is recommended.
Example: Any accidental fire near closed metallic storage of flammable solvent/liquids or explosive substance used in some process can lead to an explosion.
A combination of active and passive fire measures can reduce the impact of fire and prevent the spread of fire.
What can be done to avoid explosion:
Any activity involving the smallest risk of an explosion, now a day requires approvals from government explosives safety department as well as at local level nearly in every part of the world.
The precautionary measures involved for desired safety levels against explosion hazards include structural integrity and fire protection as a major consideration.
Designers follow some basic methods for preventing explosion and resultant damage on following a few principles.
ISOLATION OF PROCESS AND AREA:
Isolation of the process/ explosion hazard activity is a technique that is effective in reducing the damage to the areas of installation through various possible ways of isolation of the area, process and concerned services including maintaining a safe distance in overall layouts, isolation by designing different separable material flow patterns.
The isolation system designs effectively stop the pressure coming from a major explosion by absorption through a system and reduces chances of a secondary explosion to near negligible.
Some systems cut off the connection to other areas and let the pressure release out through vents in open space to have effective isolation.
The effective system design is a result of all major factors involved, including ease of operation, simplicity of the process and economy, safety being the prime consideration.
REINFORCEMENT TO DESIRED STRUCTURES AND EQUIPMENT.
At times an explosion hazard may exist but the extent of the explosion may be mild. Re-enforcement of such locations for stability and integrity of structural elements and equipment is considered enough for such locations.
However, fire protection measures are still a compulsion to avoid any complications and uncontrollable events.
SAFE VENTING OF PRESSURE BUILT-UP:
Locations, where the explosion hazard can be due to the built-up of pressure in excess of designed equipment pressure, a dedicated ventilation passage and a pressure safety release system, is installed to avoid explosions. The systems installed should however comply with sustainable environmental impact due to such pressure release to prevent an explosion.
Here also fire protection measures are important and should be in place to handle after-effects of such vent releases.
There are processes through which some gases or material dust gets generated during handling or processing ( example cola dust in a coal grading and washery plant. Aluminium dust in a paint manufacturing plant etc.) There are no economic methods of eliminating the occurrence of such dust or gases in the vicinity of a particular operation in a process.
Either temporary suspension (stoppage) of the ess till the concentration comes to desired non-hazard level is reached is conducted
There are suppression systems which can partially flood the area using an inert gas so that the concentration of oxygen is lowered to avoid the explosion.
However,these systems carry certain disadvantages for use like
- Reduced oxygen level rules out involvement of human activities without special PPE.
- Flooding of gas can be expensive compared to other measures.
- Alternative recharge of gas flooding system should be immediately possible to continue the ess to routine run.
- The repeated release of gas should not pose an adverse environmental impact.
What is required to be done to avoid damage due to fire associated with an losion:
Fires associated with explosions can be controllable by properly designed and certified fire protection systems. A combination of active fire protection systems together with passive fire protection systems always work in tandem to minimize the impact of fire and the spread of fire. The aim of active fire protection is to detect and put out a fire whether automatically or through intervention by the fire personnel. Therefore, any and all devices, systems used to detect, suppress & put out a fire are deemed active fire measures.
The major principles of Passive fire protection systems are:
- Compartmentation of big areas into smaller areas to contain the fire in a smaller controllable form in a small area (Firewalls / Fire partitions horizontal as well as vertical).
- Fire stops to prevent the spread of fire from compartment to compartment through service penetrations for a rated period (Fire penetration seals).
- Application of fire retardant coatings to retard the rate of increase and spread of fire with time and reduce overall fire intensity (Fire retardant cable coating)
- Insulate the steel and metal structures to avoid sudden collapse (Insulation plasters for Structural steel) .
- Provide passage for the evacuation of people without allowing major spread and egress of smoke and fire through the escape routes (Example, use fire-rated doors).