Passive fire protection is an integral factor during the construction of all commercial properties, from office buildings to railway stations. Sharpfibre's Mark King looks at what passive fire protection is and the important role it plays:
The Difference between Passive & Active Systems
Passive fire protection systems are included as part of the very fabric of buildings, with fire resistant walls, floors and doors all serving as examples. Each area has a variety of different solutions that are suited to varying build requirements. For example, fire resistant walls can be constructed using panels of reinforced cement with steel sheets bonded to each side, or through the application of a cementitious fire spray.
Passive fire protection products and systems are named as such because they are considered to be always 'switched on' and do not require activating in order to fulfil their role. In contrast, active fire protection devices require some form of response and/or motion in order to work. A further differentiation being that active fire protection systems are added to the building after construction, as opposed to being part of the building itself.
Active fire protection systems can be broken down into two areas: fire detectors and fire suppressants. Fire detectors serve to identify where a fire is occurring by locating heat, smoke or flames, before providing a warning of the blaze through an audible alarm and often through alerting the fire service. Fire suppressants play an active role in trying to extinguish or at least control fires; examples being sprinkler systems and fire extinguishers.
Compartmentalisation Approach
Unlike active types, passive fire protection systems never seek to extinguish the blaze. Instead their role is to contain the fire to its point of origin and prevent the flames and smoke from spreading throughout the building. This is achieved through compartme-ntalization, whereby every room or section of the building is effectively a sealed unit. In many instances the blaze will burn itself out within the contained unit, without spreading to other areas of the building.
Even if the fire does eventually spread, passive fire protection systems greatly improve the chances of those present in the building safely exiting it, by containing the blaze for a length of time. In addition, they serve to protect the structural integrity of the property and reduce the likelihood of collapse. This provides the fire services with a safer environment in which to work, as they clear the building of any remaining people and seek to extinguish the flames. Passive fire protection systems not only serve to save lives, but also limit the damage to the property, thus reducing repair costs.
Testing Criteria
Passive fire protection products are specified a requested time for which they must perform their protective role. The amount of time specified can vary between systems, dependent on where they are intended for use, with many larger commercial settings requiring 240 minutes of protection. Before products are awarded accreditation, they must first pass rigorous testing under extreme fire conditions, measured on 3 criteria:
- Stability – Systems must continue to fulfil any load bearing element for the requested time
- Integrity – Systems must prevent fire, smoke and dangerous gases from spreading for the requested time
- Insulation – Temperature of the exposed side of the system must not increase beyond the set limit within the requested time
Some passive fire systems have further requirements in addition to these 3 criteria. For example, systems utilised in multi-level buildings often have to be lightweight as not to overload the structure. Or, where explosive or combustible materials are in use within the building, the system may need to be blast resistant beyond the standard passive fire protection system specification.
A Combined Solution
Whilst it cannot be stressed just how important passive fire protection systems are, they should not be viewed as an alternative to active systems. Providing effective fire protection requires both passive and active elements working in unison and complementing the roles of one another. Through the use of a combined approach, occupants have the greatest chance of exiting the building safely and damage to the property is minimised.
