In many cases the standard type of smoke detector cannot be used for one of the following reasons:

• The presence of dust or other fine particles on a regular basis: This could be the byproduct of an industrial process in a factory or the likelihood of dust from sweeping, or the likely presence of hairspray or other substances in accomodation dormitories.

• The presence of water spray or mist due to wash-down procedures: Typically in factories connected with the food industry, meat plants, etc.

• The difficulty of protecting abnormal spaces: Such as inside electrical switchgear, sealed plenums, etc.

• The difficulty of positioning detectors or accessing for maintenance: A typical example would be a high atrium at a building entrance, or an ornate ceiling in a heritage building. Detention cells in prisons and courthouses also present unique problems.

In all these cases it is desirable to detect smoke and so give a warning of a fire at an early stage rather than use heat detection or rely on sprinklers and so only be alerted to a fire when it is generating large amounts of heat.

Solutions for difficult applications:

Time controls: Modern sophisticated fire alarm panels allow different sensitivities to operate at different times of the day. Certain output programming can also be restricted at different times. By using time controls effectively nuisance alarms during production hours can often be virtually eliminated.

Smoke Sampling: In some cases such as atriums where the height or glass structure make standard point-type detectors unsuitable the use of a sampling tube to bring the smoke to a standard detector may be the best solution. Detention cells are another likely application for smoke sampling. The new LaserFocus could be ideal in circumstances where high sensitivity is needed to counteract dilution in a large volume or where early warning is required. Alternatively an ASPIRATING SMOKE DETECTOR is a low-cost smoke sampling fanbox which accepts standard detector bases, uses 20mm tubing and monitors airflow and is ideal for such applications.

Filtered Detectors: In standard open areas where there may be either quantities of dust such as in mills or water mist from power-hoses the HARSH (Hostile Area Smoke Head) detector from Notifier can provide effective smoke detection where heat detcection would have been all that could have been contemplated in the past. Designed to operate in powder mills it is a point-type smoke detector that contains a small fan and a removable high performance filter. It requires 24v supply and the filter is monitored for blockage. It has proven to be effective in truck-wash bays and crisp factories as well as powder mills.

Multi-Criteria Detectors: By sensing both smoke and heat the combined PHOTO/HEAT or MULTISENSOR can discriminate against false activations by only responding when both smoke and heat are present. With some multicriteria detectors the smoke element can be disabled temporarily, e.g. by time-control programming in the panel. These detectors are suitable where standard smoke detectors may be prone to false alarms, such as plantrooms, small apartments, dormitories, etc.

Point-type High Sensitivity Detectors: As an alternative to the high-sensitivity smoke sampling systems such as VESDA when a small area needs early-warning detection the VIEW (Very Intelligent Early Warning Detector) from Notifier is a point-type detector that contains a small laser and offers sensitivity up to 200 times that of a standard detector. Installed on the fire alarm loop like any other detector it is ideal for protecting a small high-value room such as a communications room, archive room or server room. When used with the smoke sampling device above it can be used to give early warning detection from within equipment panels.

Flame Detectors: For rapid detection of an open flame the UV or IR sensitive flame detector may provide the best solution, especially where flammable liquids are concerned. The ultraviolet-type are the most economical, but the infra-red have the advantage of being able to see through smoke. Combined types are also available. A common application would be a UV detector looking at the burner on a boiler, where smoke detectors may be unsuitable and heat detectors would be comparatively slow in detecting a fire. Aircraft hangars would be another typical application.

Beam Detectors: Where large open spaces require smoke detection it is often preferable to use beam detectors, particularly if high ceilings are involved, such as in warehouses. Beam detectors use an infra-red beam to detect smoke. There are two approaches, one is to use a transmitter at one end and a receiver at the other, the other is to use a combined transmitter/receiver with a reflector on the far wall to return the beam. Site conditions would determine which was more appropriate. When the beam is sufficiently obscured by smoke the detector goes into alarm. Thresholds and time delays can be set depending on the equipment chosen or the system used to monitor the beam detector.

Every difficult application must be approached on an individual basis, and the devices above can be used in a variety of ways. There are many more difficult applications than those outlined and the best solution can only be determined by matching an application to all the possible alternatives and considering all the likely scenarios. 

We will be happy to give advice on the range of fire detection options and will source the appropriate equipment for each job.