Can steam operate a smoke detector?
I received an email (below) from a customer (MB) who had experienced an alarm, likely caused by steam from a shower in a washroom.
Sent: Wednesday, 17 April 2013
Subject: Smoke detector
We had a fire alarm last week in toilet/wet area due to pressure hosing. Evidently it was a smoke detector set off due to water mist.
Could you please provide feedback whether thermal detectors suffer potential false activations from minor water spray or if this is really only likely from smoke detectors?
We may have to change all smoke detectors in wet areas (i.e. change room showers etc) in to thermals.
Before I answer this question readers would be well advised to read our Principles of Fire Safety articles on Fire Detection & Alarm Systems, Heat, Smoke, Flame and Gas Detectors;
By nature, an ionisation and photo-electric smoke detector is designed to detect particulates that are the by-products of combustion.
Steam or mist describes the term for airborne water vapour, formed when water is heated and condenses in the presence of cooler air.
Steam can therefore be identified by a smoke detector as a particulate that resembles one of the by-products of combustion. The technical terms for this is deceptive phenomena and is very difficult to overcome without adversely affecting the performance of the smoke detector.
Fortunately smoke detector manufacturers and Australian Standard AS1670 provide guidance on the correct selection and application of fire detectors is a wide range of applications.
In this particular situation AS1670 provides the following guidance in Clause A2 as follows;
A2 GENERAL NOTES ON DETECTORS
Fire detectors are designed to detect one or more of four characteristics of a fire, i.e., heat, smoke, CO or flame. No one type of detector is the most suitable for all applications and the final choice will depend on individual circumstances. In some premises, it may be useful to combine different types of detectors to achieve the best results.
The likely fire behaviour of the contents of each part of the building, the processes taking place and the design of the building should be considered. The susceptibility of the contents to heat, smoke and water damage should also be considered.
The following list includes typical areas, including suggested detection devices, that should be given special consideration:
(a) Laundry/bathrooms — CO or heat with normal temperature duty and fixed temperature operation.
Notwithstanding the above, fire detection devices specifically designed for the particular applications may also be suitable.
In any automatic fire detection system, the detector has to discriminate between a fire and the normal conditions existing within the building. The system chosen should have detectors that are suited to these conditions and provide the earliest reliable warning. Each type of detector responds at a different rate to different kinds of fire. With a slowly developing smouldering fire, a smoke detector or smoke alarm would probably operate first. A fire that rapidly evolves heat with very little smoke could operate a heat detector or heat alarm before a smoke detector or smoke alarm. With a flammable liquid fire, a flame detector could operate first.
In general, smoke detectors or smoke alarms give appreciably faster responses than heat detector or heat alarms, but care has to be taken in their selection and location.
Heat and smoke detectors are suitable for use in most buildings. Flame detectors are mainly suitable for supplementing heat and smoke detectors in high compartments provided that an unobstructed view is possible, and for special applications such as outdoor storage and chemical processes employing flammable liquids.
The choice of fire detector may also be affected by the environmental conditions within the premises. In general, heat detector or heat alarms have a greater resistance to adverse environmental conditions than other types have.
All fire detectors will respond to some extent to phenomena other than fire and, therefore, care in the choice of detectors and their location is essential.1
In summary, subject to the installation and spacing requirements of Heat Detectors, Australian Standard AS1670 recommends the installation of Heat Detectors in a laundry or bathroom as a method to eliminate nuisance alarms.
Where smoke detectors have been fitted and are causing nuisance alarms, building owners are advised to get professional advice and may also require approval from the Authority Having Jurisdiction ("AHJ") prior to making any changes to their systems.
If you need further advice in regard to this matter, feel free to contact us.
- 1. Australian Standard AS1670.1-2004 Fire detection, warning, control and intercom systems—System design, installation and commissioning