The LWF Blog
Fire Engineering Design and Risk Assessment – Sprinkler Heads – Part 17October 17, 2017 10:58 am
In LWF’s Fire Engineering Design and Risk Assessment blog series for architects and others in the building design business, we are talking about sprinkler systems. In part 16, we looked at hazard classifications for sprinkler system design, in part 17, we’re going to discuss sprinkler heads.
Sprinkler heads are an important part of a sprinkler system and the most visible part to building occupants. Although sprinkler head design differs depending upon requirements, the majority act both as a detector of fire and to release water to fight the fire. The water is emitted in the form of a spray and one head can vary significantly from another in terms of droplet size, amount of water emitted and other spray characteristics.
In many cases, a sprinkler head is sealed by a heat-sensitive part which keeps the head closed until the heat from a fire breaks the glass bulb or the fusible link.
Some sprinkler designs, however, do not rely on heat-sensitive parts to control operation, but instead it is possible for fire to be detected by a fire alarm system, for example, which in turn relays that information to the sprinkler control, activating the open sprinkler heads via use of a deluge valve.
Sprinkler systems which rely on heat-sensitivity are usually designed with an operational temperature of around 30°C above the highest anticipated ‘normal’ temperature. In simple terms, this might mean that if the temperature in the room was expected to be no more than 38°C on any given hot day, including heat generated by any machinery or computer equipment, that the sprinklers would only become activated when the temperature was 68°C. A glass bulb sprinkler head with a rating of 68°C would indicated by a red bulb.
There are six other colours of glass bulb to represent temperatures between 57°C and 260°C. One such sprinkler head is used in cases of high piled storage risks. In this case, intermediate rack sprinklers are likely to be in use and they, as a standard sprinkler head, will be chosen to reflect the ambient temperature.
However, the addition of roof-level sprinklers means that these would most often be rated at 141°C (blue bulb) which would have the effect of delaying the operation of those sprinklers slightly and then as a back-up to the rack systems which would be expected to have already subdued the fire.
In Part 18, we will continue looking at sprinkler heads, beginning with how sprinkler heads are also classified by orifice size. In the meantime, if you have any questions about this blog, or wish to discuss your own project with one of our fire engineers, please contact us.
Lawrence Webster Forrest has been working with their clients for over 25 years to produce innovative and exciting building projects. If you would like further information on how LWF and fire strategies could assist you, please contact Peter Gyere on 020 8668 8663.