Quick answers
What is the difference between a fire sprinkler and a fire suppression system?
A sprinkler system uses water, and each head opens when heat reaches it. A suppression system uses gas, wet chemical or foam and is set off by smoke, heat or flame detectors.
How does a sprinkler head go off?
Heat from the fire raises the head to its set temperature. A small glass bulb breaks or a metal link melts, and water sprays out. Only the heads near the fire open.
Where are suppression systems used instead of sprinklers?
Where water could cause damage or would not work, such as server rooms, data centres, electrical panel rooms, commercial kitchen hoods and fuel or chemical stores. They usually protect one room, not the whole building.
What is a pre-action sprinkler system?
It works like a dry pipe system, but water enters the pipes only after a second trigger, such as a smoke or heat detector going off. It is used where an accidental discharge would be costly.
People often use “sprinkler” and “suppression” as if they mean the same thing. They do not. A sprinkler system fights fire with water. A suppression system uses something else, such as a gas, a wet chemical or foam, and is usually put in where water would do more harm than good or would not work. Most large buildings in India need sprinklers, and some rooms inside them need suppression as well.
Fire sprinkler systems
A sprinkler system is a network of water pipes with sprinkler heads in the ceiling. Each head is held shut by a small glass bulb or a metal link that melts. When heat from a fire raises the head to its set temperature, the bulb breaks or the link melts and water sprays out. Only the heads near the fire open, not every head in the building.
There are four main types.
- Wet pipe: the pipes are always full of water. This is the most common type.
- Dry pipe: the pipes hold pressurised air or nitrogen. When a head opens, the air escapes and water flows in.
- Deluge: all the heads are open. When the detection system triggers, water comes out of every head at once. These are used in high-hazard areas.
- Pre-action: like dry pipe, but water enters the pipes only after a second trigger, such as a smoke or heat detector going off.
Sprinklers are used in flats, offices, malls, hospitals, hotels and factories, wherever water can safely put out a fire. In India, sprinkler design follows IS 15105 and the National Building Code.
Fire suppression systems
A suppression system uses an agent other than water. Detectors pick up smoke, heat or flame, and the system releases the agent into the room or onto the hazard.
- Wet chemical systems use chemicals such as potassium carbonate or sodium bicarbonate. You find them in the hoods above commercial kitchen ranges.
- Gas systems flood a closed room with gas. CO2 and inert gases work by bringing down the oxygen level. FM-200 (HFC-227ea) works differently: it mainly takes heat out of the flame, with some chemical action, rather than removing oxygen. These systems protect server rooms, data centres, electrical panel rooms and other rooms full of sensitive equipment.
- Foam systems lay a blanket of foam over burning fuel so it cannot reignite. They are used where flammable liquids are stored or handled, such as fuel depots and aircraft hangars.
Safety in gas-protected rooms
CO2 at the concentration needed to put out a fire will kill a person in that room. That is why CO2 flooding is kept for rooms that are not normally occupied, with a lockout, a warning alarm and a time delay before the gas is released.
FM-200 and similar agents can be used in rooms where people work, but only within the human-safety limits set in NFPA 2001, the US standard for clean-agent systems. Those limits are based on the agent’s no-observed-adverse-effect level (NOAEL). Even so, when the pre-discharge alarm sounds, everyone should leave the room and shut the door.
The main differences
| Sprinkler system | Suppression system | |
|---|---|---|
| What it uses | Water | Gas, wet chemical or foam |
| What sets it off | Heat at each sprinkler head | Smoke, heat or flame detectors |
| Where it fits | Most of the building: homes, offices, shops, factories | Server rooms, panel rooms, commercial kitchens, fuel and chemical stores |
| Damage | Can cause water damage | Usually less damage, though the agent and discharge can still affect equipment |
Which one does your building need?
Often both. A suppression system protects one room or one hazard. It does not replace sprinklers for the rest of the building. The right mix depends on what is stored, how the rooms are used and whether people are inside. Get a qualified fire engineer to decide, under IS 15105 and the National Building Code, and check with your fire authority. NFPA and other overseas standards are useful reference, but they are not the rule in India.
When a room changes use, say a store becomes a server room, or a new false ceiling goes up, have the protection reviewed. Sprinkler heads hidden above a new ceiling will not help anyone.
This week, find out whether your office or society has sprinklers, suppression or both, read the warning sign on any gas-protected room, and check that stock is kept well below the sprinkler heads.
What needs attention
- Sprinklers use water and open one head at a time when heat breaks the glass bulb or melts the link above the fire
- Wet pipe, dry pipe, deluge and pre-action are the main sprinkler types; wet pipe is the most common
- Suppression systems use gas, chemical or foam and are triggered by smoke, heat or flame detectors
- Gas systems suit server rooms and panel rooms; wet chemical suits commercial kitchens; foam suits fuel and solvent stores
- CO2 flooding can kill people in the room, so it needs warnings and a time delay before discharge
Controls that reduce risk
- Have a qualified fire engineer decide where sprinklers and where suppression is needed, under IS 15105 and the National Building Code
- Fit discharge warnings, a time delay and an abort switch on gas-flooded rooms
- Train staff who work in protected rooms to leave at the first alarm
- Service sprinklers and suppression systems on schedule and keep the reports
- Review protection whenever a room's use changes, for example a store becoming a server room
Common unsafe practices
- Thinking a gas suppression system can replace sprinklers for the whole building
- Staying inside a room protected by CO2 or another gas when the pre-discharge alarm sounds
- Putting a sprinkler-protected store under a new false ceiling without moving the heads
- Assuming suppression systems cause no damage; agents and discharge can still affect equipment
- Following a US standard alone without checking Indian requirements
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