What is the difference between Active and Passive Fire Protection?

Over the years, it has become more and more apparent that buildings need appropriate fire protection. This means a bit more than the usual fire extinguisher and smoke detection systems that people usually think about when considering fire protection. These two elements are part of a bigger protection system that are mandatory in buildings at all times. There are two types of fire protection: Active Fire Protection (AFP) and Passive Fire Protection (PFP). One type of protection must not be chosen over the other. Both AFP and PFP should be used alongside one another for full fire protection in your building. It is important to understand both types so that you are confident that they are both present in your building.

What are Active and Passive Fire Protection Systems?

Active fire protection systems consist of elements such as water sprinkler systems. These are widely used in buildings to protect the storage of vessels, process plants and warehouses. The job of the active fire protection system is to extinguish or control the fire or provide adequate exposure protection to prevent a domino effect. For some buildings, foam pourers or mixed water monitors may be a more appropriate method than sprays or sprinklers. Other specialised systems include the use of inert or halogen based gases which are used for flooding enclosed spaces.

Passive fire protection systems are used for protecting against building failure. It generally consists of a coating of fire resistant insulating media generally applied to a steel surface. It is often used where water or other active fire protection systems are inadequate such as remote locations. Fire walls are another form of passive fire protection that are used to prevent the spread of a fire and the exposure of equipment to thermal radiation. An important requirement of deciding which fire protection system to use in each part of the building is the likely duration of the exposure to fire as passive fire protection is only effective for a short time (typically 1-2 hours).

General Principles

The owner of the building must be able to demonstrate that it has an effective plan for the fighting and containment of a fire if it were to break out. The following factors should be considered when determining whether active or passive fire methods are required.

• Fire hazard caused by substances
• Toxicity of substances and the smoke that is produced
• Inventory size
• The frequency of hazardous operations undertaken on site
• The distance to other hazardous installations
• Available access to fight any possible fire
• Fire fighting capability of on site emergency response team
• Response time of nearest fire brigade
• Resources available to nearest fire brigade

Design of System

Active fire fighting systems need to be reliable and the design should demonstrate this. The designs of these systems should conform to standards such as the Health and Safety Executive’s BS 5306 Code of Practice for extinguishing installation and equipment.

As part of these standards, valves and cabling for the system should be a safe distance from any hazardous installation and should be able to withstand the effects of fire and heat. The system should be supplied by a secure water supply which should include back up diesel pumps where appropriate and it 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.

The Choice of Fire Fighting Media

The selection of your fire fighting media will depend on what you are wanting it to do. This may be to extinguish the fire, control the fire or provide exposure protection. The types of fire fighting media are:

• Water
• Foams
• Inert gases
• Chemical Powders
• Halons

Water is not recommended for low flash point liquids but is used widely for fire control and exposure protection. Foam is more effective for low flash point substances and is used widely on liquid fires. There are various types of foam but the most common is protein foam. Specific foams have been formulated to fight specific fires such as solvent based or to improve extinguishing properties. Active fire protection systems can deliver agents such as inert gases, chemical powders and halogen based gases. A common use for these are in control panels and switch rooms; however, there has been less use of halon based media over the years due to its impact on the environment.

The Choice of Passive Fire Protection

There are a number of passive fire protection systems to choose from including:

• Mortar based coating
• Intumescent coating
• Sublimation coating
• Mineral fibre matting
• Earth mounds

Protective based systems are normally sprayed on to the surfaces. A reinforced glass fibre scrim or steel wire gauze is applied to prevent cracking of the coating under fire conditions and provides additional strength to resist the power of high pressure water jets frequently used by the fire brigade. It is further protected by a weather protective top layer. The performance of the fire resistance of the coating is dependent on its thickness. Fire walls are sometimes installed in process and storage areas to prevent the spread of fire and protect equipment from thermal radiation. Firewalls are normally built from brick, concrete or masonry and the number of openings in them should be kept to a minimum.

A Summary

Active and passive fire protection systems, together are important to a building’s overall fire safety. AFP uses systems that actively try to put out a fire, whilst PFP prevents the spread of fire and smoke. Just because one is installed and working does not mean you don’t need the other. AFP takes action in putting out a fire but should not be relied upon solely. There are times, particularly during the winter, that sprinkler systems often fail due to frozen pipes, roads could become icy and water supplies could freeze which all delay a firefighter from doing their job. PFP compartmentalises a building into smaller sections to prevent the spread of fire and smoke, while also providing occupants enough time to evacuate. As effective as this is, PFP is not effective by itself either. Therefore, to ensure total fire protection, both systems must work together in unison.