FIRE PROTECTION - Water extinguishing

FIRE PROTECTION

Fire prevention is one of the most essential safety measures on board a chemical tanker. Discipline is needed in the daily routines. Watch out for obvious things such as:

look out for all leaking flanges, valve and pump glands

keep pump room bilges free from cargo spills

see to it that steam pipe insulation does not get soaked with oil or cargo

check cargo tank and pump room atmosphere for cargo vapours before starting any work there

do not steam a cargo tank simultaneously with washing

use flame‑proof lights in cargo tanks and pump rooms

check pump glands and bearings regularly for heating

cigarette lighters in the cargo tank area to be forbidden

observe cargo vapour release during loading and take action if vapours reach accomodation areas

check cargo pump glands for heating

take active part in safety‑drills and get acquainted with all the safety equipment

instruct newcomers on board on safety procedures

get to know your ship, cargo handling gear etc.

The formal responsibility for surveillance of the fire fighting equipment normally rests with the respective

National Authority, but is in some cases delegated to the Classification Society. It rests with the Owner and the Master to keep all equipment in order and to provide additional means for any cargo not covered by the intent of the Rules of the National Authority. The IMCO 'Bulk Chemicals Code' ref (25), Chapter III, see Appendix 6, gives some general guidance on necessary equipment on board and indicates the best means for extinguishing fires for a number of cargoes. Similarly the ICS Tanker Safety Guide ref (t) gives more detailed information on the choice of extinguishing method to be used for the individual cargoes

Several methods of extinguishing fire can be used. Without going into more complicated details let us list the most important aspects of the matter of fire fighting in the cargo area on chemical tankers:

Water extinguishing 

All ships are fitted with means for fire fighting with water. Although not ideal, water can be used on fires in a majority of chemical cargoes, the advantage of course lying in its abundant supply. Water is, however, not very effective in extinguishing fires in very gassing cargoes such as naphta, gasolines or liquified gases; it may, however, then be used as a cooling medium in connection with dry powder or other methods of fire fighting in order to avoid dangerous 'back flash', see 5. 03.

Water should be applied to the base of the fire by means of water fog jets, water pressure preferably not lower than

9 kp/cm 2. The fog serves as an excellent heat radiation shield in front of the. operator. Never direct a solid jet of

water on to a burning liquid surface, the effect will only be that burning liquid is splashed around, thereby making the fire bigger. 'Water fog shall be applied with a strategy of chasing the fire succesively away from the operator. The fog may be swung from side to side to cover a wide front of attack. Do not apply water fog on top of foam; it will cause the foam to disintergrate and may possibly in so doing expose the surface of the flammable cargo to the risk of a back flash.

It is a good practice to have water hoses with fog jets connected to the fire main on deck during cargo handling.

The IMCO Code ref (25) advices against water for most products in the relevant 'Summary of minimum

requirements'. This list, however, is meant to emphasize that other extinguishing media are a first choice and are to be provided on board.

Do not hose water into conc sulphuric acid, an eruption of liquid may occur!

Foam extinguishing

Foam extinguishing is provided on many chemical tankers and on a majority of modern large crude oil carriers. Of

all the extinguishing methods in the IMCO Code foam is pre ferred, but the use of dry powder is generally accepted as an equivalent method.

Water soluble chemicals, e g acetone, alcohols, have a tendency to break down conventional foams and render them in effective. Chemical tankers should therefore be provided with alcohol‑ resistant foam ( 'alcohol foam'). On the data sheets in the ICS‑Tanker Safety Guide, Chemicals, ref (1) it is especially stated for every product if alcohol‑

resistant foam is a 'must'.

Heavy foam (water/air ratio abt 1:15) is in modern tankers distributed by means of several foam guns which can cover the entire deck area, by means of portable jets or by means of long portable pipes. The latter are intended to be used for the introduction of foam into a tank on fire without risk for the foam to dip underneath the liquid surface. Foam has a limited extinguishing effect on very gassing cargoes: the gases penetrate the foam and burn on top of it. Foam is a good method for fire prevention: a deck area or a free cargo liquid surface can be protectively foam covered if there is a danger of fire. If a liquid surface is to be foam covered: direct the foam onto a bulkhead or other vertical surface and let it spread from there and float out to cover the entire liquid surface. The foam operator may have to be shielded against heat radiation by means of a water spray.

Medium density foam (water/air ratio abt 1:200) is used in enclosed spaces such as pump rooms. Medium density foam can be produced very simply in fixed distribution jets under deck, in e g a pump room, by using the ejector power of the water stream to draw air into the water foam mixture. Medium density foams are intended to cover the bottom part of a compartment. The installation is very simple and relies on starting the fire-pump only.

Light foam (water/air ratio 1:200 ‑ 1:1000) is only used in enclosed spaces such as engine and pump rooms. It is usually produced by means of a water driven fan which blows up the foam mixture. The foam is intended more or less to completely fill up the compartment in question.

Light foam is sometimes used as a preventive blanketing medium when 'hot work' (e g welding) has to be carried out in a cargo tank, which may not have been possible to clean perfectly. The whole tank bottom is then foam covered, leaving only the work location free. Of course the tank has to be guaranteed gas free before starting hot work. Similarly neighbouring tanks can be protected before welding is started on bulkheads.

Dry powder extinguishing

Many new chemical tankers use dry powder extinguishing Dry powder system as the main fire fighting method in the cargo tank extinguishing area.

There are to be found centralized powder systems with possibilities of discharging several thousand kgs of powder. Release boxes and hose f eels are strategically located on deck so that any point can be reached by two hoses, each being usually max 25 m length. On smaller vessels self‑contained powder containers of 1000‑3000 kgs are located in small deckhouses.

As mentioned above the IMCO‑Code accepts dry powder as equivalent to foam. Dry powder has decided limitations, which are explained below.

The extinguishing effect of dry powder originates mainly from an inhibiting effect on the combustion. The smothering and cooling effects are small.

Dry powder has a particularly good extinguishing effect on larger volumes of burning gases and strongly vapourizing liquids, as compared with other means of fire fighting. But it has virtually no cooling effect on any steel, cargo liquid or other matter that has become heated from the fire. Once the flames have been thrashed out with dry powder there is a great risk for a fire back flash which can be more violent than the original fire. At a major fire therefore, the fire area should be cooled down with water fog as much as possible prior to application of powder. Water cooling must be continued after the flames have been extinguished If a fire can be fought immediately after its outbreak and only little heating has occurred one should of course immediately start with dry powder, not awaiting water fog assistance.

Common types of dry powder have a tendency to break down a foam layer. Therefore the two methods should be avoided being used together. Some new powders are claimed not to have this deteriorating effect on foam.

Always place two dry powder extinguishers at hand on deck aft of the cargo manifold, when loading /unloading.

'Total flooding' system for pump rooms. Inert gas for fire protection

I I

Many tankers have a‑CO2. total flooding' system for the cargo pump rooms. This is a most effective method for extinguishing a fire in a closed compartment. Certain dangers, however, are involved

make sure the room has been evacuated before admission of CO 2' No one will have a chance of escaping once the gas has been admitted.

the released CO 2 may assume a strong electrostatic charge which may cause incendive sparks. This is of no consequence if the room is already on fire, but if the room is to be inerted with CO 2 as a preventive, measure this should only be done knowing that the room is gas free.

Lately halogen gas total flooding systems have been installed on a trial basis. This gas does not possess the above disadvantages and is easier to install.

Inert gas in the cargo tanks, see 3. 05, is to be considered a preventive safety measure only. The delivery capacity of inert gas generators etc is far below the requirements for active fire fighting.