After halons were phased out of fire suppression systems back in the 1990s, it created a need for alternatives. The challenge was that halons were very effective in extinguishing most types of fires, electrically non-conductive, safe for limited human exposure, and leave no residue. The disadvantage of halons and why there was a ban placed on them is due to their strong ozone depletion potential. Over the past several decades, several fire suppression agents and technologies have emerged. In this post, we will explore aerosol fire suppression systems.
How Aerosol Suppression Agents Work
Aerosol fire suppression uses a combination of microparticles and gaseous matter to flood the protected area. The particles are in a vapor state until discharged from the device. On release, a chain reaction creates the solid particles and the gaseous matter to suppress the fire. Because of the chemical reaction, the temperature of the canisters can heat up to 4000°F at discharge, and there have been instances where reflash occurs from the temperature produced by an aerosol suppression system. A cooling block needs to be added to the device to prevent the rise in temperature. Additionally, due to the size of the particles, they remain airborne for a longer time, potentially leaving less residue on critical components.
To suppress a fire, the suppression agent must break the fire tetrahedron, by reducing the fuel, oxygen, heat, or hindering the chain reaction of the three elements. As long as there are enough heat, fuel, and oxygen present, a fire will keep burning. The aerosol fire suppression system removes one of the three fire elements to stop the combustion reaction of the fire. Upon discharge of the system, the large concentrations of microparticles surround the flame. On contact, the particles cool the flame and absorb the flame’s heat to suppress the fire. The particles can also serve as an oxidizer if the suppressant agent includes potassium nitrate. The particles bind with the free radicals that sustain the fire’s combustion to produce by-product molecules such as potassium hydroxide and water. It disrupts the combustion process until the fire is out.
How Effective and Safe are Aerosol Systems?
Aerosol fire suppression systems can be effective in suppressing Class A, B, and C fires. However, the ability and effectiveness to suppress the fire will depend on the concentration levels of the particulates near the flame, location of other flammable materials, and type of fuel involved. The system can be equipped with either electrical or automatic fire detection and activation. Aerosol suppression is available for both a total flooding environment and for local applications.
During the design and install of a system, it is crucial to pay close attention to the proximity of critical components. Depending on the location, aerosol systems can leave residue on key components that can damage them. This is the case when installing in tight areas like the nacelle of a wind turbine. Another risk factor is that if a fire starts in an occupied space like a nacelle of a wind turbine or a sealed space with limited or no airflow when the aerosol suppression system activates, the chemical reaction can cause adverse inhalation effects on humans. It also creates an aerosol cloud that causes visual impairment and makes the egress from space more challenging. There have been two tragic incidents from false discharges of aerosol systems in a bank vault, which killed eight and injured seven, and on a fishing vessel, which led to one death. For local applications like within CNC machines, after the system activates, you will need to wait for some time before you can vent the aerosol suppression agent and assess any damage.
What's the Best Fire Suppression System?
When selecting a fire suppression system, many factors need to be considered, including how large of an area you are trying to protect, what are the essential components within the space, and if the space will or could be occupied. As halons become unavailable for use, the development of other effective fire suppression agents occurred. Having several options for fire suppression, you need to find the best fit for your application and the area you are trying to protect.