Automatic fire detection systems, when combined with other elements of an emergency response and evacuation plan, can significantly reduce property damage, personal injuries, and loss of life from fire in the workplace. Their main function is to quickly identify a developing fire and alert building occupants and emergency response personnel before extensive damage occurs. Automatic fire detection systems do this by using electronic sensors to detect the smoke, heat, or flames from a fire and providing an early warning.
If your workplace uses a fire detection system that was designed and installed to meet the fire protection requirements of a specific OSHA standard, it must also comply with the "Fire Detection Systems" standard. [29 CFR 1910.164]
This section will help you achieve the maximum benefit from your fire detection system by addressing the following issues:
If an OSHA standard specifically states that you must install a fire protection system, then you are required to follow this standard.
For example, if you install an automatic fire detection system to satisfy the alarm and signaling requirement of the "Fixed Extinguishing Systems" standard, then you are also required to comply with the "Fire Detection Systems" standard. [29 CFR 1910.160 and 29 CFR 1910.164] But if you install a system only for insurance purposes and not to satisfy any OSHA regulation, you do not need to comply with this standard. However, employers not required to comply may find that the standard offers guidance that may permit them to more effectively protect employees and property in the event of a fire.
Fire detectors work by sensing one or more products of fire. The three most common detectors are:
Smoke detectors detect the visible or invisible smoke particles from combustion. The two main types are ionization detectors and photoelectric detectors.
The ionization detector contains a small radioactive source that is used to charge the air inside a small chamber. The charged air allows a small current to cross through the chamber and complete an electrical circuit.
When smoke enters the chamber, it shields the radiation, which stops the current and triggers an alarm.
These detectors respond quickly to very small smoke particles (even those invisible to the naked eye) from flaming or very hot fires, but may respond very slowly to the dense smoke associated with smoldering or low-temperature fires.
In a photoelectric smoke detector, a light source and light sensor are arranged so that the rays from the light source do not hit the light sensor. When smoke particles enter the light path, some of the light is scattered and redirected onto the sensor, causing the detector to activate an alarm. These detectors react quickly to visible smoke particles from smoldering fires, but are less sensitive to the smaller particles associated with flaming or very hot fires.
Heat detectors are normally used in dirty environments or where dense smoke is produced. Heat detectors may be less sensitive, but are more appropriate than a smoke detector in these environments. The most common heat detectors either react to a broad temperature change or a predetermined fixed temperature.
Heat detectors use a set of temperature-sensitive resistors called thermistors that decrease in resistance as the temperature rises. One thermistor is sealed and protected from the surrounding temperature while the other is exposed. A sharp increase in temperature reduces the resistance in the exposed thermistor, which allows a large current to activate the detector's alarm.
Flame detectors are line-of-sight devices that look for specific types of light (infrared, visible, ultraviolet) emitted by flames during combustion. When the detector recognizes this light from a fire, it sends a signal to activate an alarm.
Assure that all devices and equipment constructed and installed to comply with this standard are approved for the purpose for which they are intended. [29 CFR 1910.164(b)(1)]
Fire detectors should be selected based on the burning characteristics of the materials present and the nature of location they will be used to protect.
Ionization or photoelectric smoke detectors are designed to identify a fire during its smoldering or early flame stages and will meet the needs of most areas containing primarily wood, paper, fabric, and plastic materials. During combustion, these materials produce a mixture of smoke types with detectable levels of both large and small smoke particles. Smoke detectors are suitable for:
NOTE: Some locations are unsuitable for smoke detectors due to the potential for unwanted alarms -- work areas, kitchens, stairs, shafts, high air flow locations, areas that are dusty or dirty, as well as outdoor areas.
Heat detectors are ideal for areas where flammable gasses and liquids are handled or any area where a fire will quickly cause a large change in the surrounding temperature. Heat detectors are also suitable for:
Flame detectors are best for protecting:
Protection of Fire Detectors:
Detectors that are installed outdoors and need to be shielded from the weather to work properly or may be exposed to corrosive environments must be protected from corrosion. Provide a canopy, hood, or other suitable protection (such as a non-corrosive coating) for detection equipment, requiring protection from the weather. [29 CFR 1910.164(d)(1)] In order to keep detection equipment operable, they must be located away from or out of contact with materials or equipment which may cause physical damage or be protected by a cage or metal guard. Locate or otherwise protect detection equipment, so that it is protected from mechanical or physical impact that may render it inoperable. [29 CFR 1910.164(d)(2)]
All detectors must be securely mounted to a solid surface, such as screwed to a junction box with a mounting plate or other appropriate method that prevents them from putting pressure or stress on attached wires or tubing. Assure that detectors are supported independently of their attachment to wires or tubing. [29 CFR 1910.164(d)(3)]
Number, location and spacing of detecting devices:
The number, spacing, and location of detectors must be based on design data obtained from 29 CFR 1910.164(f):
General Guidelines for Placing Fire Detectors:
Over time, dust, dirt, and other foreign material can build up inside a detector’s sensing elements, resulting in reduced sensitivity, which can limit the amount of warning time given during a fire. Dirty or dusty detectors can also result in unwanted alarms that can desensitize occupants to the alarm system or produce more serious behavior (such as disconnecting the system altogether).
To avoid malfunctions and unwanted alarms and to make sure your fire detection system will perform as expected in the event of a fire, you are required to:
All fire detection equipment must be returned to normal operation as soon as possible after being tested, used, or accidentally activated. [29 CFR 1910.164(b)(2)]
NOTE: You are also required to have spare detection devices and components readily available in the workplace or from a local supplier to ensure prompt restoration of the system.
The following applies to fire detection systems used for specific applications:
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