Gas-Based Suppression Systems
GAS-BASED SUPPRESSION SYSTEMS
INTRODUCTION
Gas-based suppression systems are active fire protection systems that are used for the purpose of protecting human lives, the environment and goods safely and efficiently. Their uses are covered by various standards and regulations.
Gas-based suppression systems by total flooding date back to at least the year 1920, when Walter Kidde introduced CO2 systems in the US. However, they had limitations in terms of human safety, since:
- It produces a sharp drop in the temperature of the protected room; the temperature down can reach as low as-70º
- CO2 displaces oxygen making the atmosphere unbreathable
- The gas is discharged in the form of fog, so that evacuation of occupied areas becomes difficult
By the 60s it became very popular to use gaseous agents by total flooding. The best known system was Halon 1301, but in 1994 it was prohibited for environmental reasons, namely its effects on depleting the ozone layer. Clean agent fire protection systems then replaced the traditional Halon 1301 as they do not present (or present very low) potential harm to the ozone layer.
Main extinguishing agents today
In reference to the mechanisms of action to prevent fires, and taking into account the fire-triangle, we can stablish the following clasification:
Reducing the oxygen level:
- N2, Ar, mixed and CO2.
At O2 levels of <15% (approx.), the combustibility of the material is reduced, stopping the chain reaction.
Reducing energy:
- FK-5-1-12, HFC 227ea, etc.
- Cooling: Cooling below a certain temperature, breaks the combustion reaction.
- Chemical mechanisms: Breaking the combustion chain, eliminating the radial carbon that propagates the combustion reaction.
Meanwhile it is important to indicate that gas-based suppression systems comply with the regulations and technical rules or at least for special cases apply the Favourable Technical Suitability Evaluations.
Extinction by gas-based suppression systems should aim to completely extinguish any fire event, whilst prioritising the safety of people. These systems are designed around concentrations of extinguishing agents which can pose a serious risk to people, possibly resulting in death if the relevant rules are not followed. Therefore, the uses of gas-based suppression systems in occupied areas are permitted however the concentration levels of the agent must take into account the safety of people as well as other important factors.
It is important to highlight that PEFIPRESA has experts in each area of fire protection who design on the basis of using the most adequate system in terms of maximum levels of security through the study of risk, and always consider the essential features; the volume of the enclosure and its construction, availability of storage place, external factors, etc.
AUTOMATIC EXTINGUISHING SYSTEMS USING CO2 OR OTHER GAS
Gas-based suppression systems are basically used in locations where fires need to be extinguished quickly, and where it is essential to prevent subsequent damage caused by the effects of the extinguishing agents or waste.
In extinguishing systems using gaseous agents, the discharge sequence is normally initiated automatically by means of a fire detection and alarm system, although it can also be activated manually. Once the alarm has been triggered and the programmed delay has elapsed, the extinguishing agent is discharged into the fire zone. Any fans or air conditioning equipment will be conditioned and the ventilation gates and doors will close automatically, obtaining the necessary tightness and the minimum and conditions to achieve the level of extinction calculated during the design phase.
As important as it is to study the type of agent, design and installation, it is also fundamental to evaluate other influences such as the discharge speed and working pressure of the extinguishing agent, restrictions in the distribution of Tee and limitations due to the length of vaporization in halogenated agents, etc. For this reason, experience and knowledge play a vital role in the effectiveness of these systems.
The following are some of the relevant aspects to be studied prior to design and installation:
Discharge speed: Inert agent and CO2 vs halogenated agent.
As can be seen in the above, the discharge speed of clean agents is significantly lower and can provide a significant advantage. Therefore, the activation and extinction times are much lower compared to inert gases and CO2. The fire can be controlled and extinguished in a shorter timeframe, which implies an important advantage to be taken into account in fires of rapid development and propagation.
Volume of occupation: Inert agent, CO2, halogenated
As shown in the image above, the volume of space the cylinders consume can vary greatly depending on the type of agent used. Clean agents use much less space in comparison to inert gases. Given the importance of saving space in the type of facilities being protected (data centres, control centres, electrical rooms, etc.) this too needs to be considered when studying the optimal protection system, the client’s needs and satisfaction.
Vaporization length (Consideration Vds). Halocarbon systems
Once the extinguishing agent has been fired and passes through the nozzles a small part of the agent will travel a certain distance in a liquid state before converting into gas. That distance is called the vaporization length. It is important to recognise that obstacles (pillars, cable trays, cabinets, etc.) will prevent the agent from reaching the gas state.
- This distance must be obtained from the design calculation.
Pressure relief area
The pressure relief area in the enclosure must also be calculated for design purposes.
The calculations should also be made for the maximum permissible overpressure data for the structure of the enclosure, the minimum area to be contemplated for the installation in the enclosure of bidirectional (Halocarbon) and unidirectional (Inert and CO2) grids.
The graph below shows recent environmental pressures for several clean agents in discharge of the system, where we can observe the difference between Halocarbon agents; HFC-227ea, HFC-125 and FK -5-1-12, as well as the inert gas, IG-541.
Enclosure integrity test for the protected risk “Door Fan Test”
In gas-based fire extinguishing systems, it is also essential to highlight the importance of carrying out the “Door Fan Test”. This is a simulation that shows how the agent will behave in terms of sealing. It should be considered in the evaluation phase to verify that the minimum sealing conditions are met and maintain the design concentration during the determined time stipulated in the standard/regulation for the selected extinguishing agent, in order to prove the viability of the chosen extinguishing agent.
For the design of these systems, even though they are fire protection, they must be delegated their design and installation as well as maintenance in true experts in the field with proven experience. PEFIPRESA’s parent company MINIMAX, provides us with support, expertise and the latest developments through their R+D+I specialists based in the trials and testing centre in Germany. We also have access to the latest technical and regulatory information due to our collaboration in drafting them through Tecnifuego for UNE.
