What is a sprinkler system?
A sprinkler system is a network of pipework and heat-activated heads that discharges water onto a fire automatically. Only the heads over the fire operate, not the whole system.
The misconception that every head goes off at once comes from film and shapes how people think about the water damage risk. In practice a fire is usually controlled by a small number of heads, and the water used is a fraction of what a fire service would need later.
Because they act early and automatically, sprinklers change what the rest of the strategy has to achieve, which is why a building's fire strategy and its sprinkler provision are read together rather than separately.
They need their heads unobstructed and their valves in the right position. A closed valve makes an entire system inert while leaving it looking exactly as it should.
In practice
A warehouse where racking has been raised closer to the heads.
The racking change was an operations decision taken on a Tuesday. The system was designed for a different storage height and arrangement.
Suppression design depends on what is stored, how high and how it is arranged, and ordinary commercial changes invalidate the basis of it.
The control valve being open is necessary and nowhere near sufficient.
What goes wrong in practice
- Stock stacked too close to heads, blocking the spray pattern.
- Heads painted over during redecoration, which changes how they operate.
- Valves left closed after maintenance, with nothing on site showing the system is out of service.