During 2018-2019 there were nearly 45,000 primary fires or incidents of fire in dwellings and other buildings in England alone. This resulted in 213 fatalities (source: Govt.UK Fire Statistics). If we look at the UK, every year the fire and rescue service is called to an incredible 600,000 fires that result in over 800 deaths and over 17,000 injuries. Many of these could possibly have been prevented. How can we reduce the loss of life in these situations and reduce the significant human and financial losses inflicted?
The ‘Fire Triangle’ – How Fires Start
Four things must be present simultaneously in order to produce fire:
- enough oxygen to sustain combustion, e.g. air, oxygen from cylinder stores or piped system, chemical (oxidising agents)
- enough heat to raise the material to its ignition temperature, e.g. hot surfaces, naked flames, smoking, electrical equipment
- Some sort of fuel or combustible material, e.g. flammable liquids, flammable gases, flammable solids, combustible solids
- and a chemical chain reaction, the exothermic reaction that is fire.
The important thing to remember is that if you take any one of these four elements away you will not have a fire, or the fire will be extinguished. Fire safety is based upon the principle of keeping fuel sources and ignition sources safely apart.
Buildings will have two types of fuel or fire load, a temporary fire load and a fixed fire load. The temporary fire load is the number of combustible materials and items that people bring into the building. Typically, this will include furniture, computers, curtains. The fixed fire load is that of the building itself and all component parts and systems needed to make it work. This includes installed cables, ceilings, walls, floors, fittings. We may not see the thousands and thousands of miles of cables installed as in the case of multi-level buildings they are frequently encased in flexible conduit and ducting systems.
The cable insulation alone can present one of the biggest fixed fire loads in the building. Should fire break out a very important consideration is to restrict the spread of smoke and flames while supporting the critical emergency systems providing vital time for safe evacuation and shutdown procedures.
Active or Passive Fire Protection Systems?
When discussing a buildings fire protection system your first thoughts are likely to be around the alarm and sprinkler systems. Active Fire Protection (AFP) systems require some amount of action or motion in order to work efficiently. It is the role of active fire protection equipment within the fire containment process to detect, alert and seek to eliminate the fire hazard. Active fire protection equipment covers such items as fire/smoke alarm systems, sprinkler systems and fire extinguishers.
Passive Fire Protection (PFP) components try to find ways to contain or slow down the spread of a fire from one area to another. Passive Fire Protection (PFP) are the components of systems that section or compartmentalise a building. Methods of compartmentalising are carried out by using fire-resistance-rated walls and floors by subdividing the building into areas to limit the spread of fire and smoke. Its aim is to help to slow or prevent the spread of fire/smoke from one room to the next and essentially providing occupants more time for evacuation and limiting the amount of damage done to a building. Passive systems include fire or smoke dampers, fire doors firewalls/floors.
Do we need both active and passive fire protection systems? Well yes, we do. Consider for a moment what could happen if any part of the fire protection system fails to work due to the lack of maintenance or component failure? There is much more to it than this and there needs to be a partnership of active and passive fire protection methods deployed. Both types need to work together during a fire if they are to help protect and save lives.
Why would a cable manufacture be concerned with Passive Fire Protection systems?
Frequently built-in fire protection is hidden from view between floors, above a suspended ceiling or in cavity walls as part of the fabric of the building. Fire containment is critical to the fire performance of the building’s design.
Steve Williams, Commercial Manager, Wrexham Mineral Cables said: “Effective fire-stopping plays a critical role in containing a fire at its source thereby reducing its effect on the primary building structure. The degree of spread is controlled by creating fire-resisting compartments which subdivide the building. By necessity, mechanical and electrical services can breach compartment walls and floors thereby permitting the failure of integrity and the insulation to occur on any gaps around services that have not been adequately fire-stopped. Fire-stopping products must be able to provide enough insulation to the penetrating services. It needs to reduce the temperature-rise along any conductive materials and be in accordance with the required insulation criteria of the fire-separating element.”
We need to reduce the risk of fire spreading and ensure the effective protection fire separation forms a complete barrier. Walls and floors need to provide an equivalent level of fire resistance through to any openings. The passing of services, such as heating pipes or electrical cables, through fire-resisting partitions, leave gaps through where fire and smoke could spread. This should be rectified by fitting the correct fire stopping solutions for that construction. When considering fire resistance, a component or construction of a building needs to satisfy a stated period. Generally, this is described as 30 minutes fire resisting or 60 minutes fire-resisting under BS EN 1363-1,45 BS 476-732.
Steve continued: “In recent years there have been calls for better installation of services through passive fire protection equipment. Firewalls should be completely sealed. But what if the equipment designed to aid protection, was actually the cause of the flame spread?” We focus our attention into our active or passive fire protection systems to ensure we have stopped the fire path, but have we really done all that we can? Installations often need to break through a firewall to install cables. By doing this we need to check if we have really met the relevant fire standards by putting a cable inside a covered conduit sleeving through the firewall. “When you think about it, we go to the process of installing the correct fire stoppers, barriers and applying intumescent materials, only to break a hole right through them to install the power cables. These cables in themselves may contain propagating coatings and under real fire, conditions spread the risk of fire. Even if we install the cable into a pipe or conduit, we are providing a toxic smoke or fire route right through the actual fire containment.”
“Cables are part of the power critical areas such as the emergency escape routes and are there to maintain the circuit integrity for powering the fire alarms and sprinklers in critical failure conditions. As little as a small pencil hole crossing the fire barrier can fill with toxic smoke and spread. This may falsely set off smoke detectors in the wrong areas and they may spread the fire along the inside of the pipe by exploiting the cable coating itself as the fuel to spread that fire. Shockingly when in real fire conditions these coated conduits provide a flame path from one zone directly through to another.”
Inside the conduit oxygen is limited, but the smoke and toxic fumes from the decomposing soft skin insulations are highly flammable. These gases will migrate along the conduits to the junction boxes, switch panels, distribution boards. What if this was to occur in a potentially explosive atmosphere such as on a ship or submarine. They have strict lockdown procedures when a fire is detected but imagine the scenario!
A proven and tested way to overcome these dangerous fire paths is to carefully consider your choice of cable. An effective choice is to use Mineral Insulated Cable. Steve explained: “An MI cable will not allow propagation of an explosion inside the copper tube and the cable is unlikely to initiate an explosion even during circuit fault conditions. The copper sheathing will not contribute fuel or hazardous combustion to fire and cannot propagate a fire along the cable within a building. The cable is inherently fire-rated without the need for any additional coatings. It will survive designated fire tests representative of actual fire conditions. MIC cable is approved by electrical codes for use in areas with hazardous concentrations of flammable gas and approved by electrical codes for use in areas with hazardous concentrations of flammable gas in air;” See video from Wrexham Mineral Cables on this link https://youtu.be/2YVy2RCbNMY.
Mineral cables are a good installation choice as they are smaller in diameter than other soft skin coated cable and they have no need for additional conduit protection or glands. When sealed in one simple installation they give complete water, air and gas-tight seal. The unique construction of MIC Cables means the conductors are protected by compacted magnesium oxide with a melting point of over 20000C. They have a copper sheath with a melting point of over 10800C. Unlike any other type of fire-resistant cable, no polymers, tapes or armouring are used, so this type of cable will operate directly in the heart of a fire and continue to safely carry a load in temperatures in excess of 10500C for over three hours. Not only all of this from a mineral cable but its’ unique construction means it has its own built-in conduit (copper sheath), with zero plastics or polymers and survives BS 6387 C, W & Z. It will continue to operate fully immersed in water and under high-pressure fire hose making it an ideal choice to use with active fire protection equipment such as fire alarms, sprinkler systems.
The ultimate fire survival cable from Wrexham Mineral Cables are manufactured to meet British and European standard. Achieving endorsements & certifications from many regulatory bodies including BRE – LPCB, the world-renowned approvals body for fire performance products, Warrington Fire Research Centre and London Underground. The termination glands and increased safety seals are SIRA – ATEX EExd approved.
For more information, go to www.wrexhammineralcables.com