United States
Hong KongFire sprinkler systems
Wet pipe, dry pipe, pre-action and deluge are the four broad types. Design follows NFPA standards referenced by the code, and the general contractor coordinates clearances, penetrations and obstructions.
Designed by specialists to NFPA standards. What the exam asks a general contractor is which type suits a situation and what coordination it needs.
The four types
| Type | Pipe contains | Suits |
|---|---|---|
| Wet pipe | Water, always | Heated buildings - the commonest by far |
| Dry pipe | Pressurized air until a head opens | Unheated spaces where water would freeze |
| Pre-action | Air, with a separate detection release | Spaces where accidental discharge is costly |
| Deluge | Open heads, water on detection | High hazard, where fast total coverage is needed |
Wet pipe is simplest and fastest. Dry pipe exists because water in an unheated space freezes, and the delay while air discharges is the trade.
Obstructions
A sprinkler head needs clear space below it. Ductwork, light fittings, shelving and stored material can all obstruct the spray pattern, and any of them may arrive after the system was designed.
The sprinkler contractor designed to an empty ceiling. Everything installed afterwards can compromise coverage, and coordinating what goes where beneath heads is the general contractor's job.
Penetrations
Sprinkler pipe through a rated assembly needs a rated firestop, exactly as any other penetration does.
Freezing
A wet system in an unheated space will freeze and burst, which floods the building it was protecting. Attic and canopy areas are where this is missed. Coordinate below the heads.
Inspection and testing
Systems are tested before acceptance and inspected periodically afterwards. Handover documentation is part of closeout.
Common questions
What are the sprinkler system types?
Wet pipe, dry pipe, pre-action and deluge.
When is a dry pipe system used?
In unheated spaces where water in the pipe would freeze.
What is a pre-action system for?
Spaces where accidental discharge would be costly, since a separate detection event must occur before water enters the pipe.
Why do obstructions matter?
A head needs clear space below it to distribute water, and anything installed afterwards can compromise coverage.
Who coordinates around sprinklers?
The general contractor, since the sprinkler design assumed an empty ceiling.