The FM-200, heptafluoropropane with the chemical designation HFC-227ea, was developed as a substitute for Halon 1301, which is harmful to the environment, degrades the ozone layer and breaks down into two harmful products at very high temperatures: HBr (hydrogen bromide) and HF (hydrogen fluoride).
Advantages of gaseous extinguisher FM-200
The FM-200 extinguishing mechanism is based approximately 80% on the physical basis and 20% on the chemical basis. The main effect of a very rapid gas supply into the room with fire is cooling the flame. As a result of this, the temperature of the burning material falls below the flash point, the flame is reduced and moves away from the burning substance. In the end, the fire is completely extinguished. The added pure nitrogen provides the needed pressure and it pushes the FM-200 gas from the cylinder resulting in cylinder pressure similar to that of halon, i.e. about 25 bar.
FM-200 has a boiling point of −16.6°C, vapour pressure at 21°C is 4.04 bar, its GWP (“Global Warming Potential”) is 3300 and its lifetime in the atmosphere is from 31 to 42 years. The effect of heating a typical system with the FM-200 during the lifetime of about 15 years is equal to heating the earth with a 100 W bulb.
After numerous tests carried out by various independent laboratories, it was determined that the FM-200, at a concentration that ensures successful extinguishing, is completely harmless to human health. This gas is even used as a propellant in aerosol drugs for asthmatic patients. Attestations for harmlessness were, among others, also issued by the following international laboratories or agencies:
- US EPA (“Environment Protection Agency”),
- Germany, “Hygiene Institute” (Health Institute),
- France, Ministry of Health,
- England, HAG (“Halone Alternatives Group” – a group researching possible replacements for Halon),
- Australia, the Ministry of Health.
The US EPA has stated some of the typical characteristics of the FM-200 in its bulletin:
- it is the most effective agent of all the suggested replacements for Halon 1301,
- it has no harmful effect on the ozone layer.
- It is authorized for use without restrictions in extinguishing systems with full flooding, and also in rooms with a permanent presence of people.
Layout and main components of the system
The main elements of the FM-200 extinguishing system are a gas cylinder with a valve, an activator which opens the valve on the command of a fire alarm central control panel in the event of fire, a pipeline which provides gas flow from cylinders to fire extinguishing nozzles…
A gas cylinder with a valve stores the required amount of gas. Sizes are standardized by volume and range from 5 L to 243 L. The amount of gas is calculated separately for each system. The cylinders are filled upon request with a 0.5 kg precision. The valve is an integral part of the cylinder.
An activator electrically or indirectly pneumatically opens the valve on the command of a fire alarm central control panel when there are multiple cylinders in the system. Valves on all cylinders of one system must open simultaneously as this is the only way to ensure the prescribed time of gas release and to achieve the correct concentration.
The pipeline provides gas flow from cylinders to fire nozzles. The pipeline should be designed for a maximum pressure of 33 bar (the pressure in the cylinders is 25 bar). When designing it is necessary to know the exact length of individual sections of the pipe so that a computer program can calculate the required pipe cross-section, which should be neither too large nor too small.
The pipeline may be divided into several parts with T links, which may be side links (the majority of the gas flows in the same direction it came in) or main links, in which the gas is diverted by 90° from the direction of arrival; the quantity is divided approximately in half.
Fire extinguishing nozzles disperse the gas from the pipeline to the affected room. Two types of nozzles are available: 360° and 180°. The first are placed in the middle of the room, while the others are placed against the wall of the room, some 10 cm below the ceiling.
The mechanical activator provides a fully mechanical activation of gas release independent from the fire alarm central control panel.
The characteristics of designing an extinguishing system with FM-200
The designing of an extinguishing system with FM-200 has specific features as any other extinguishing system. It is important to use the correct concentration under exactly specified conditions. All properties of the gas and the area where the system is to be installed need to be considered and proper ratios need to be determined.
- The gas concentration for computer rooms with a temperature of 20 °C is designed for 7 volumetric %. The concentration of certain substances may also be higher, for example 8.8% for heavy transformer oils.
- The gas mass is the volume of the room x 0.5846 kg/m3.
- The cylinders are scaled in the following sizes: 5 L, 8 L, 16 L, 28 L, 51 L, 81 L, 142 L and 243 L.
- The gas mass in the cylinder ranges from 0.48 to 1.12 kg/L of the cylinder volume.
- The duration of gas release to the room ranges from 6 to 10 s, the recommended time is 9 to 10 s. If the duration is too short, it causes intense air turbulence, and 10 s is the maximum time allowed.
- Multiple cylinders can be bound into a parallel system to protect larger rooms.
- 180 nozzle: The maximum floor covering area is 12.2 x 13.4 m2, the maximum distance from the nozzle to the border of the ground plan coverage (spatial diagonal D) is 14.7 m. The maximum height of the coverage is 3.6 m, if the room is higher, it should be virtually vertically divided into two parts and each should be protected with its own nozzle. The minimum height of the room (technical floor) is 30 cm (surface coverage only 7.6 x 7.6 m2). The allowed gas flow through the nozzle ranges from 4 to 80 kg.
- 360° nozzle: The maximum floor area of coverage is 12.2 x 13.4 m2, the maximum distance from the nozzle to the limits of the ground plan coverage (spatial diagonal D) is 9.8 m. The maximum height of coverage is 3.6 m, if the room is higher, it should be virtually vertically divided into two parts and each should be protected with its own nozzle. The minimum height of the room (technical floor) is 30 cm (surface coverage only 7.6 x 7.6 m2). The allowed gas flow through the nozzle ranges from 4 to 80 kg.
- One cylinder or a parallel connection of a larger number of cylinders can charge a number of nozzles in the same or in different rooms. You must take care that a precise concentration of gas enters the room within the prescribed time. The division is performed by T links and the split ratio is regulated with diameters, pipe lengths and the size of openings in the fire nozzles.
- The T distribution link may split the flow only on the same height level, but a division in which a part of the gas goes from the T link downwards and a part goes horizontally or upwards, is not allowed. The allowed division at the central T link is 30% to 70% to one branch, and the rest to the other branch, while at the side T link, 10% to 30% of the gas can go to the side branch and the remainder goes to the main branch.
Important properties for extinguishing are as follows:
- It is classified as a “pure agent” – it leaves no residue after extinguishing
- The extinguishing is very successful (guaranteed extinguishing effect)
- It works very quickly (10 seconds)
- It can be used for extinguishing a wide range of fires
- It is safe for people
- It does not harm the environment
- It does not harm sensitive equipment
- Automatic fire extinguishing systems with this gas are efficient
- It does not need a lot of storage space
- It can fully replace the Halon extinguishing system
- It can be supplied in the long term and it is commercially available, Zarja Elektronika has the gas permanently in stock in our own filling station
The advantages of FM-200:
- Many international attestations and certifications
- Low pressure liquefied gas storage
- Computer-supported design that is tested and attested even for extremely complex systems
- Completely harmless to human health in concentrations required for fire extinguishing
- Suitable for extinguishing a wide range of fires
- Minimum impact on ozone and heating of the earth
- Very quick and effective extinguishing effect (up to 10 seconds)
- It can be implemented into the most demanding extinguishing systems