FIRE AND EXPLOSION PREVENTION

(Material courtesy of A.N.T.A.  publications, edited html extracts Ranger Hope © 2008,)

 

Dangers of Fire and Explosion

Causes of Fire and Explosion  

Petrol                                    

Distillate                               

Fuel and Fuelling arrangements       

Refuelling Safety                          

Fire and Explosion Emergencies      

 

 

 

Dangers of Fire and Explosion

 

In this section the specific dangers of petrol and LP gas are especially highlighted. But you must not forget, if diesel fuel comes into contact with hot surfaces, the results may be destructive and lethal. Diesel burns furiously once started. Do not underestimate its dangers.

On board a vessel, fire and explosion is particularly dangerous. The vessel is a closed and restricted space, and is usually harder to get out of than land-based workplaces.  The presence of large volumes of fuels, increases the danger.

At sea, emergency services are not readily at hand, and the environment can be hostile if you have to leave the ship.

In ships the dangers associated with fires and explosions are high, and because assistance may be so far away, the focus is on fire and explosion prevention. The rules and procedures applying to shipping are laid down to try to prevent fire and explosion happening.

Fire and explosion fighting equipment and abilities are also important, because we all know, if anything can go wrong, it will.

 

 

 

Causes of Fire and Explosion

There are a number of characteristics which you should know, in relation to fuels. These are explained and compared below:

 

Flash Point:  If a fuel is heated to it’s flash-point, it will give off a vapour which will ignite momentarily or flash, if ignited by a spark or flame.

Fire Point: If a fuel is heated to it’s fire-point, it will give off a vapour which will burn continuously, if ignited by a spark or flame.

Auto Ignition Temperature (A.I.T.):   Also called Spontaneous Combustion Point or Self Ignition Point. This is the minimum temperature at which a fuel will burst into flames with no external ignition source.

Flammability Range:  This is the percentage range at which a flammable gas in air can be ignited. Below the range, there is not enough fuel in the air to burn. Above the range, the fuel/air mix is so rich it cannot burn.

Density Relative to Air:  Is an indication of whether a gas will rise or sink in air. Air is one. Gases heavier than air (more than one) will sink and ‘pool’ in a vessel.  Gases lighter than air (less than one) will rise.

 

The table over the page compares common fuels often found in marine vessels.

 

 

 


Petrol

Distill-ate

LPG

Hydro-gen

Acetylene

Flash Point (°C)

(–) 40
°

75 - 80°

  

  

  

Fire Point (°C)

(–) 35°

80 - 85°

  

  

  

Auto Ignition Temperature (°C)

   390°

  350°

  500°

  590°

   340°

Flammability Range %

1.4 - 7.6

1.4 - 8

2.4 - 9.6

  4 - 74

  2.5 - 80

Density Relative to Air

1.5 ±

1.5 ±

   1.5

  0.1

   0.9

 

This table tells you that:

·        petrol vapour can catch fire well below freezing temperature

·        diesel must be quite hot to catch fire, but will burst into flame by itself at a much lower temperature than petrol

·        hydrogen and acetylene will both burn over an extremely wide fuel/air range

·        hydrogen is much lighter than air.

By regulation, the closed flash point of fuel used at sea must be 60°C or more. The flash point of kerosene is 43°C.

The A.I.T of turpentine vapour is 250°C. Keep it away from exhaust pipes which may run as high as 750°C.

 

Petrol

 

Petrol is very dangerous because:

·        it is highly flammable and will burn furiously

·        it will vaporise at normal temperatures, and form explosive gases. These tend to be heavier than air and will settle in the bottom of the vessel

·        in higher temperatures, it will produce more explosive vapours.

·        if petrol vapour trapped in a container or confined space is ignited, the results can be lethal

·        burning petrol will float on top of water, and be carried through drains and deck plates. Do not try to put out burning petrol with water

·        static or electric sparks from switch-gear, or naked flames where petrol vapour is present can result in a serious explosion or fire.

When petrol is used on a vessel, steps are taken:

·        to ensure that petrol will not leak into the vessel during refuelling operations

·        to minimise petrol spills or leaks in the vessel

·        to develop procedures and techniques to minimise the risks of spill

·        to ensure that engine rooms are well ventilated to remove vapours.

 

Distillate

 

Diesel will produce a flammable vapour if it is heated, but will not do so at normal temperatures. However, it will burst into flame more easily than petrol if accidentally sprayed onto hot exhausts, etc.

 

 

Fuel and Fuelling Arrangements

 

To minimise the risk from fuel and re-fuelling operations (whether petrol or diesel), safe practice precautions can be outlined as below:

·        Tanks shall be filled from deck fill-plates located outboard so that any fuel spillage flows overboard. The use of deck-plates which allow an overflow of fuel or fuel-vapour to gravitate (sink down) into the bilge, or under floors or into lockers is absolutely prohibited.

·        The deck fill-plate must be electrically connected to the tank by an unbroken metal filler-tube or a copper wire not smaller than 7/1.35.

·        The filler-tube will extend into the bottom of the tank.

·        Tanks must be vented outboard with a tube of at least 14.9mm diameter. Metal tubing is preferred, but neoprene or nylon is acceptable.

·        A suitable screw plug should be provided in the tank for sounding the fuel level.

·        Fuel lines must enter the tank from the top when fuel pumps are used.

·        A shut-off valve must be located as near to the tank as possible. The leak-proof diaphragm type is preferred, the needle type is acceptable, but the push-pull type is not acceptable.

·        Plastic fuel lines are not acceptable, except for outboards with portable tanks. Metal fuel lines must have a wall thickness of at least 0.889mm. They must have adequate size, and be adequately secured throughout their length. Fittings must be of the flared-type compression fittings are not acceptable.

·        At the engine, a section of flexible metallic or armoured neoprene fuel tube will be used, to minimise the risk of fracture due to vibration.

·        Carburettors shall be fitted with a functional flame arrestor. If not of the down-draught type,  drip trays covered with fine bronze (flame arresting) gauze mesh must be located under the carburettor.

·        Fuel must not be carried in plastic containers.

 

 

Liquefied Petroleum Gas (LPG)

 

LP gas is dangerous because it is heavier than air, and will flow down into bilges, under-floor spaces and lockers.  Leaking LPG appliances or fittings could slowly fill the vessel with a pool of explosive gas and blow the vessel of the water if the gas is ignited.

 

 

LPG Fittings and Installations

The USL Codes (Engineering) specify tight requirements and specifications for LPG fittings and installations. These must all be followed.

Some requirements of the USL specifications are outlined as examples and for explanation below – Note!  These must not be taken as a complete list of requirements:

·        Tanks, pipes, fittings and appliances must all meet stated specifications

·        All installations and testing must be carried out by an approved person

 

Figure 66:  Vented LPG Locker
                        Arrangement

 

 


 

·        Cylinders must be fitted with a manual stop valve and a safety (pressure) relief device.  The regulator also has a safety relief device
(Note! Under emergency conditions, these relief devices can send out streams of explosive gas or flame–where would you like them to be?)

·        A cylinder must not be installed or stored, even temporarily, inside a deckhouse or below decks, or within 1 horizontal metre of an opening leading below (with the exception of a small cylinder fitted as an integral part of a portable appliance)

 

In open or partially decked vessels, the Authority may permit cylinders, regulators, and associated equipment to be installed in a special locker (see Figure 66) which:
-     is sealed from the vessel interior, and is lined with fire resistant material.
     
-     located above the water line, and fitted with a vent to drain leaking gas away.

-     be accessible from the top only, with an openable vapour tight cover.
     

No part of an LPG installation shall pass through a space containing
machinery, explosives or highly combustible substances.

·        Appliances must be fitted with a flame failure shut-off to automatically shut-off the appliance if the pilot flame or main burner flame goes out. They must be located in a ventilated space and sited where they will not be blown out. They cannot be located below weather decks (without approval.

·        The appliance must be located so any person can escape if a fire occurs at the appliance.

 

Instructions for Using LP Gas

An instruction plate must be placed in a conspicuous position near one of the LPG appliances. The wording on the instruction plate shall be:

(a)       All appliances shall be turned off and cylinder valves closed when the vessel is not in use or while refuelling is in progress.

(b)       Cylinder valves shall be immediately closed in an emergency.

(c)        Close appliance cocks before opening cylinder valve.

(d)       Check connections at appliances, regulators and cylinders periodically for leaks, with soapy water or it’s equivalent.

(e)       Never use a match or flame when checking for leaks.

(f)         In the event of a gas leak, immediately stop all engines, shut off all gas appliances, and close cylinder valves. Then ventilate the vessel until the air is clear.

(g)       Do not stow empty cylinders in the machinery space.

(h)        In the event of fire, immediately close the cylinder valve.

(i)         Close valve and fit safety plugs to all spare cylinders not connected, whether full or empty.

(j)         No additions or alterations shall be made to the LP gas system without permission from the Authority.

(k)        Crew should familiarise themselves with the odour of unburnt LP gas to assist in the early detection of leaks.

(l)         All permanent ventilators, flues and vents should be regularly checked to make sure they are clear.

 

Hydrogen Gas from Storage Batteries

 

During the normal operation of a low voltage DC marine electrical system, when the batteries are fully charged, not much hydrogen gas is produced by the batteries. However, only 4% of hydrogen is needed in the air to catch fire.

Batteries will produce much more hydrogen gas, and are more dangerous during charging and discharging operations. The higher the charge/discharge rate, the more flammable hydrogen gas is produced.

Hydrogen gas is much lighter than air and will quickly float away from a well ventilated vessel. However, in a closed non-ventilated space, e.g. container, locker, or room, the gas will collect and form an explosive mix. Any spark or flame may then ignite the mix.

 

To minimise the risk of hydrogen explosion from storage batteries:

·        don’t operate the cells with vent caps removed–hydrogen inside the battery can ignite and explode the battery

·        battery storage areas must be well-ventilated at the top to let the gas escape, particularly during periods of heavy charge or discharge

·        keep cigarettes, sparks and flames away from batteries

·        switch off battery chargers before disconnecting them

·        remove all electrical load from batteries before disconnecting them.

Re-fuelling Safety

To minimise the risk of fire and explosion during refuelling operations:

·        use correct (earthed) fuel delivery systems

·        shut off LPG systems at the tank during re-fuelling operations

·        keep cigarettes, sparks, flame, and  ‘hot work’ away from re-fuelling area

·        avoid spills and clean up after re-fuelling.

 

Fire and Explosion Emergencies

 

In the event of fire and/or explosion on board, you must instantly assess the size of the problem, and what it might develop into. You should use your assessment to quickly work out the appropriate course of action (for example, it is not necessary to send a ‘MAYDAY’ and abandon ship because a waste bin has caught alight unless the bin is under your cargo of TNT....).  Your assessment process should be continuous- is the problem developing and becoming more dangerous, or is it under control.

 

Your level of response must grow with the problem, and for this reason it is difficult to lay down a specific procedure for all fires. However, for a serious fire or explosion, the following general emergency procedure is a guide as to what you should do:

·        raise the alarm

·        stop the engines, shut off the fuel cut-off valve and LPG tank valve

·        remove crew from danger if possible, and arrange life saving first-aid for the injured if this delay does not threaten the safety of others

·        decide if radio calls, signals, and the preparation of lifebuoys (L.S.A) are necessary in this emergency, and take appropriate action

·        activate fixed fire fighting equipment

·        determine type of fire, and select appropriate fire-fighting equipment to attack fire shut off ventilation system, and keep fire doors and vents closed

·        check adjacent compartments (they may need cooling down)

·        assess your progress and determine what action to take.

 

After an emergency is over, an Incident Report will need to be prepared.