How Does A Fire Suppression System Work?
Fire suppression systems help avert disaster by controlling and extinguishing a fire before it gets the chance to spread. In order to understand how a fire suppression system works, we explore how a fire ignites and the different stages of development a fire typically goes through.
With detailed information about fire ignition and growth, we see how fire suppression systems use extinguishing agents to combat fires.
What Is A Fire Suppression System?
A fire suppression system is an engineered group of units designed and built to extinguish fires through the application of a suppressing agent. The suppressing agents used include CO2, chemical, and inert gases.
Fire suppression systems differ from fire sprinkler systems in that they use gas as a suppressing agent rather than water. Fire sprinkler systems may cause water damage to equipment and electronics, whereas gaseous fire suppression systems are able to extinguish fires without causing further damage to business assets.
Moreover, fire sprinkler systems are ineffective against certain types of fires (ie. electrical fires), making gaseous fire suppression systems the preferred option in environments such as data centres, server rooms, and manufacturing facilities.
Fire suppression systems aim to protect a facility, the occupants of a facility, and the assets contained within a facility from fire damage.
What Causes A Fire To Ignite?
Three elements need to be present at the same time for a fire to ignite, namely oxygen, heat, and fuel. These three elements, often referred to as the “fire triangle”, come together to form a chemical reaction that results in a fire. The process of these three elements combining to form a fire is known as combustion.
A fire cannot sustain itself without all three elements of the fire triangle in place. Removing any one of the three elements will cause a fire to subdue and die out. Increasing one or more elements of the fire triangle will cause a fire burn with increased intensity.
Heat represents the ignition source necessary for a fire to start. Heat sources can include the sun, lightning, hot surfaces, cigarette embers, and electrical sparks. Once started, a fire produces its own heat to continue the combustion process and further maintain itself.
Heat is also responsible for the spread of fires as it flows from areas of high temperature to areas of low temperature, pre-heating fuel in its path. This transfer of heat causes the fire to grow and to spread across a wider area.
Fuel is any kind of combustible material that will burn. Fuel sources that feed a fire may include paper, oil, wood, gases, flammable liquids, fabrics, plastics, and rubber.
As some materials burn more easily than others, fuel sources are usually characterised by moisture content, size, shape, and quantity. These characteristics determine the heat/temperature at which a combustible material will ignite and how easily a fire will burn.
The last component of the fire triangle is an oxygen supply, also known as an oxidising agent. Without oxygen a fire will not burn. The earth’s atmosphere consists of approximately 21% oxygen, and most fires only need about 16% to burn.
This means that the earth’s air contains enough oxygen to support the chemical process that occurs during a fire. When fuel burns, it reacts with oxygen in the surrounding atmosphere to release heat which drives combustion.
Different Stages of Fire Development
A fire will typically develop in four different stages. These four stages are Incipient, Growth, Fully Developed, and Decay. In order to respond to a fire appropriately, it is important to understand what stage of development a fire is in.
The first stage of development is the incipient stage. During this stage a fire ignites and combustion begins. The fire is in its beginning stages and has not yet spread beyond its immediate vicinity. Smoke has not yet reduced visibility in the vicinity, and occupants are still able to breathe.
The heat level of the fire is relatively low and people are able to escape from the area without too much difficulty. It is easiest to suppress a fire and escape from a vicinity during this stage.
As a fire continues to develop, it enters the growth stage. At this stage a fire generates enough of its own heat to spread and ignite surrounding fuel sources. The growth stage can be characterised by a significant increase in room temperature, along with a layer of smoke forming above a fire that usually accumulates around the ceiling of a room.
The growth stage represents a critical stage of a fire’s development, where the fire begins to spread rapidly before reaching the point of “flashover”. The flashover point occurs when a fire has generated so much heat that all combustible materials within the fire’s vicinity ignite spontaneously. A flashover can be described as the rapid spread of a fire that engulfs an entire room in an instant.
A fire then progresses to the fully developed stage. During this stage energy release is at its greatest and temperatures are at its highest (reaching between 700°-1200°C).
It represents the peak of a fire’s intensity and the most dangerous stage in a fire’s development. Fully developed fires are characterised by darkened or black smoke, thick and dense smoke, substantial heat, and visible exterior flames.
Once all available fuel is consumed or oxygen is depleted, a fire enters the decay stage. This is the longest stage of a fire as the fire diminishes and eventually dies.
It is critical to limit a fire’s exposure to combustible materials and oxygen during this stage. Even during the decay stage, a fire has the potential to reignite.
How Fire Suppression Systems Detect Fires
In order to have the best chances of extinguishing a fire, fire suppression systems need to detect a fire during its early stages of development as close to the start as possible. The earlier a fire is detected and extinguished, the less damage the fire will cause.
When a fire ignites during the incipient stage it is easiest to suppress and control the fire. Once a fire begins to spread during the growth stage it becomes significantly harder to control.
Fire suppression systems are able to detect fires during its early stages through heat, smoke, flames, odours, and other warning signals. Smoke detectors identify smoke in the air from a fire, flame detecting sensors detect the presence of a flame or fire, and thermal detectors respond to high temperatures associated with a fire.
Once a fire is detected an alarm system will activate to alert occupants of the presence of a potential fire, in order to evacuate a vicinity to safety. The fire suppression system will then initiate the steps for action to control a fire before it gets the chance to spread.
How Fire Suppression Systems Extinguish Fires
Fire suppression systems aim to control and contain a fire before it gets the chance to spread out of control. This is achieved by extinguishing a fire through the application of a suppressing agent that eliminates either the heat or oxygen that a fire needs to sustain itself.
Introducing these suppressing agents to a fire disrupts the chemical reactions that occur during a fire which restricts the growth of a fire and ultimately puts a fire out.
Different fire suppression systems use different gases as a suppressing agent. The most commonly used gases included:
- inert gases
- and Halon 1301 (although halon fire suppression systems have been discontinued)
FST is a registered Halon Bank Vendor. Should you need to dispose of old/obsolete systems please contact our office.
As an alternative to gaseous fire suppression systems, water mist fire suppression systems use water as an extinguishing agent. Water mist systems spray micron water droplets that create a blanket of mist across a large surface area.
The mist is able to absorb the heat from a fire, lower the temperature in an enclosure, and cool a fire down. It also displaces the oxygen in a room to suffocate and extinguish a fire.
For more information on the different kinds of fire suppression systems commonly used, visit our 5 Types of Fire Suppression Systems blog.
FST Fire Suppression Systems
Fire and Security Techniques is a South African-based manufacturer and supplier of high-tech automatic fire suppression systems throughout Africa. We are a dedicated supply and trade support company.
We offer a wide range of fire suppression systems, along with all of the supporting services needed to maintain these systems throughout their lifetime. FST provides high-quality solutions to protect your facility and minimize damages in the event of a fire.