What is passive fire protection and where is it used?
Passive fire protection, sometimes referred to as PFP, is a method of fire protection that seeks to slow the spread of a fire and smoke by containing it within the compartment of origin for a limited period of time. PFP is an integral part of building construction, heavily regulated by building codes. Passive fire protection measures usually involve the structural or mechanical inclusion of a fire resistant material around the compartment in question. It’s the opposite of active fire protection, which usually uses some sort of electrical component to detect and then suppress the fire.
Where is passive fire protection used?
The most common use of the term passive fire protection is in relation to buildings and structures. In the UK, PFP measures are tested and regulated under British Standard 476, ensuring that appropriate measures are taken to protect the life of users or occupants of the building and also to maintain structural integrity and limit damage in the event of a fire.
As electric and hybrid vehicles become more and more common, PFP is increasingly being discussed as an important consideration in the design and manufacture of these vehicles in order to ensure the safety of drivers and passengers and mitigate potential fire risks.
Passive fire protection in electric and hybrid vehicles
PFP is a particularly important consideration in electric (EV) and hybrid (HEV) vehicles, as opposed to internal combustion engine (ICE) vehicles, where the fire risk is mainly contained to the engine compartment, EVs and HEVs have potential fire sources in multiple sections in the vehicle. The main protection zones include auxiliary heater and AC, the battery compartment, the electrical cabinet, and the engine compartment (most relevant in HEV which still have an internal combustion engine).
Passive fire protection and thermal runaway
PFP is particularly integral to the battery compartment of an EV, due to the risk of a process we’ve covered many times called thermal runaway. For a quick refresh, thermal runaway is an unstoppable chain reaction which can occur in a lithium-ion battery when the temperature increases, and the cathode breaks down, leading to a positive feedback loop and rapidly increasing temperature.
The conditions that lead to thermal runaway can be grouped into four categories.
- Electrical abuse – caused by overcharging or discharging beyond the recommended charge window. This can cause lithium plating or dendrite formation on the anode, which over time can begin to pierce the separator and lead to a short circuit.
- Thermal abuse – where the battery is operating in or exposed to high temperatures. An internal temperature in the range of 90-120°C will cause the solid electrolyte interphase (SEI) layer to decompose. At temperatures above 200°C, the hydrocarbon electrolyte will decompose and begin to release heat.
- Mechanical abuse – physical damage to the battery cell caused by impact, or inflicted during installation or repair. Penetration, pinching or bending leads to electrical shorting and localised heating.
- Internal short circuit – a failure of the separator, causing contact between the cathode and the anode, which can be caused by any of the previously mentioned conditions.
Passive fire protection solutions for electric vehicles
A common PFP measure in electric vehicles is the use of high temperature insulation around the battery pack and in between the battery cells. A variety of heat-resistant materials can be used, but mica is an excellent candidate.
Mica as PFP
Mica laminated sheets can be used to create thermal barriers in and EV battery packs in order to help with passive fire protection and contain the spread of fire to the battery compartment. Able to withstand temperatures of up to 1000°C, mica is also non-flammable and incredibly durable and versatile. Mica laminate can also be used to create compression pads – which apply mechanical pressure to the battery cells to allow for “breathing” and tolerance when the battery is charged or exposed to extreme temperatures, which can help to further mitigate the risk of thermal runaway occurring.
Elmelin work closely with automotive manufacturers to design, develop and produce passive fire protection solutions for electric, hybrid and alternative fuel vehicles. Our mica-based insulation solutions help to increase safety without compromising on performance. If you’d like to find out more, get in touch.