FIRE PROTECTION TECHNIQUES

Investigation of active and passive fire protection techniques

Sub subject: Chemicals and foams

Investigation of active and passive fire protection techniques

Sub subject: Chemicals and foams

Introduction

Active fire protection systems such as water sprinkler and spray systems are widely used in the process industries for protection of storage vessels, process plant, loading installations and warehouses. The duty of the fire protection system may be to extinguish the fire, control the fire, or provide exposure protection to prevent domino effects. For some applications foam pourers or fixed water monitors may be a more appropriate method of delivery than sprays or sprinklers. Other more specialised systems using inert gases and halogen based gases are used for flooding enclosed spaces.

Passive fire protection can provide an effective alternative to active systems for protecting against vessel failure. This generally consists of a coating of fire resistant insulating media applied to a vessel or steel surface. It is often used where water or other active protection media supplies are inadequate, such as in remote locations, or where there are difficulties with handling fire water run-off. Fire walls are another form of passive fire protection that are used to prevent the spread of fire and the exposure of adjacent equipment to thermal radiation. An important criterion in deciding which system is most appropriate for fire exposure protection is the likely duration of the exposure to fire as passive fire protection is only effective for short duration exposure (1-2 hours).

General principles

The operator should be able to demonstrate that it has an effective and practical plan for the containment and fighting of fires on its process installations. The following site factors should be considered in determining whether active and passive fire protection measures are required:

fire hazard posed by substance;

toxicity of substances and the smoke produced;

inventory size;

frequency of hazardous operations;

distance to other hazardous installations;

available access to fight fire;

fire fighting capability of on site emergency response team;

response time of nearest fire brigade;

resources available to fire brigade.

Design of system

Active fire fighting systems need to be reliable and the design of the system should demonstrate this. The design of fire fighting systems should conform to specified standards such as BS 5306 Code of practice for extinguishing installation and equipment[6] and Fire Offices Committee 'Tentative rules for medium and high velocity spray systems'.

The location of items such as the foam and water sources should be a safe distance from any hazardous installation. Critical valving and instrument cabling located on the protected installation should be capable of withstanding the effects of fire and heat.

The system should be supplied by a secure water supply which should include items such as backup diesel pumps where appropriate. The design must ensure that the active fire protection system is not starved of water due to other demands on the water supply system during a fire.

Choice of fire fighting media

The selection of media will depend on the required duty. This may be to extinguish the fire, control the fire, or provide exposure protection. Types of fire fighting media are:

Water;

Foams;

Inert gases;

Chemical ...