A number of sites rely on sensitive electrical equipment spread across a wide range of spaces to function properly. Switchrooms, control rooms, generator enclosures, PLC and MCC cabinets and control systems can all be present in facilities across multiple industries. All these components carry an ignition risk, and all of them are vulnerable to how a fire is suppressed, as well as the damage a fire might cause.
Traditional sprinkler systems are a reliable and cost-effective means of fire suppression for many site areas. However, around electrical plant, there is a danger that the volume of water discharged from a sprinkler brings a new set of damage risks. These include short circuits, corrosion on contacts and circuit boards, and water pooling in cable trays and floor voids. Water damage can seep further than fire damage, and equipment untouched by fire may still require drying or even replacement before it can work again. Water damage can extend the time a production line or facility stays offline.
Wherever limiting damage to electrical systems and operational recovery time matters, there are two alternative means of fire suppression. These are water mist and gaseous systems, both of which are designed around the same question: what condition will the equipment be in after discharge?
Water mist systems
High-pressure water mist fire suppression systems can operate at pressures of around 120 bar, depending on their design, forcing water through specialised nozzles and atomising it into fine droplets. These finer droplets have a much larger combined surface area than the water from a traditional sprinkler, which helps them to absorb heat rapidly. Then, as they evaporate, they displace oxygen around the flame, while the mist itself blocks radiant heat from spreading.
For electrical equipment, the key difference between water mist and traditional sprinkler systems is volume. A water mist system uses a fraction of the water a traditional sprinkler uses. There is also comparatively less water run-off onto cabling and into floor voids, and equipment that is affected by water can dry out and return to normal function sooner.
Appropriately designed and tested water mist systems may be suitable for certain generator rooms, machinery spaces and industrial process areas, depending on the hazards and equipment present. It tends to fit particularly well where the hazard combines electrical equipment with hydraulic oils, lubricants or other combustibles. Water mist systems should be designed, installed and maintained in accordance with the relevant applicable standards, which may include, depending on the exact system, BS 8489 and BS EN 14972.
Gaseous systems
Gaseous suppression works by total flooding. Rather than targeting the seat of the fire, a gaseous system fills an entire protected enclosure with an extinguishing agent which then suppresses the fire. This extinguishing agent is either an inert gas or chemical agent.
- Inert gases: These include nitrogen (IG-100) and argon (IG-01), both of which reduce the oxygen concentration of a room to below the level needed for combustion.
- Chemical agents: These include compounds such as FM-200 and FK-5-1-12. These agents work by interrupting the chemical chain reactions necessary for combustion.
Because gaseous systems are non-conductive and leave no water or extinguishing residue, they can reduce clean-up requirements and support faster recovery, subject to appropriate inspections and safety checks. After activation, some systems may be brought back online more quickly, which in turn can make gaseous suppression a better choice for control rooms, switchrooms, telecoms facilities, or anywhere with expensive, sensitive electronic equipment.
Gaseous fire suppression systems depend on a room’s ability to hold the extinguishing agent at design concentration, until the fire is extinguished. Reignition is a risk wherever a room cannot flood properly. Gaseous systems are designed and maintained to BS EN 15004.
Choosing the right system
No single system suits every site. A mechanical plant may need water mist in its generator room and gaseous suppression in its control room. Deciding which system is suited to which area depends on a fire risk assessment.
A fire risk assessment identifies the hazards on site and establishes whether active suppression is needed. It takes into account:
- The specific hazard
- Room geometry and enclosure integrity
- Occupancy
- The requirements of the site’s insurer
The insurer’s requirements are increasingly decisive. Insurers often require suppression on specific plant, such as industrial ovens or generator enclosures, as a condition of cover. An insurer’s requirements can shape the system specified. Getting the assessment right at the outset avoids retrofitting later. It also means that when a system does discharge, both the fire and the damage are contained.
Fire suppression that limits water damage
When it comes to protecting sensitive electrical equipment, a suppression system shouldn’t pose its own risk. Limiting water damage can matter as much as limiting fire damage.
Water mist uses a fraction of the water of a conventional sprinkler, which reduces run-off, the risk of conductivity and drying time around electrical plant. Gaseous suppression removes water altogether: it leaves no residue and allows equipment to return to service shortly after discharge.
Many sites use both, matching each system to the hazard and the equipment in each area, as decided in a fire risk assessment. But in either case, a site’s system should be designed to contain a fire quickly and limit a site’s potential downtime.
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