Sprinklers are being considered more often for the preservation of our national heritage, particularly since the loss of Windsor Castle.

They are normally risk assessed as extra Light or Ordinary hazard.

Extra Light indicates light fire loads such that 2.5mm density is adequate (this means that during operation of one sprinkler each square metre of floor under the sprinkler head has enough poured on to it to gain a depth of 2.5mm of water every minute). Ordinary hazard requires 5mm depth every minute.

The sprinklers are easily hidden in panels or ceilings, however pipework is less easy to hide. Most older houses, however, are built in huge proportions and have large voids in floors and service corridors of no significant architectural value. So careful planning can keep the feed pipework out of sight.

Water damage from sprinklers is a major concern, but once a system is completed the likelihood of failure is extremely low. The latest approved plastic pipe has further reduced risk by not requiring hot work on sites.

In the event of a fire the nearest sprinkler will operate within minutes and immediately suppress or douse the fire sending an alarm to the watch keepers. If the fire spreads rapidly then more sprinklers will activate. 68% of fires are suppressed by three sprinklers or less.

Assuming the fire is attended within five minutes, the water used would be in the region of fifteen litres per square meter or four gallons per square meter. Whilst this looks pretty horrendous (like a glass of water thrown on your carpet!), it will dry out. The alternative is ash.

Fire Defence has protected major historic buildings, including Longleat House.