Heat and Smoke Detectors

FIRE SIMULATOR predicts the effects of fire growth in a 1-room, 2-vent compartment with sprinkler and detector. It predicts temperature and smoke properties (Oj/CO/COj concentrations and optical densities), heat transfer through room walls and ceilings, sprinkler/heat and smoke detector activation time, heating history of sprinkler/heat detector links, smoke detector response, sprinkler activation, ceiling jet temperature and velocity history (at specified radius from the flre i, sprinkler suppression rate of fire, time to flashover, post-flashover burning rates and duration, doors and windows which open and close, forced ventilation, post-flashover ventilation-limited combustion, lower flammability limit, smoke emissivity, and generation rates of CO/CO, pro iri i post-flashover. 

Sprinklers and fire protection systems are required by NFPA Codes, but are often dependent on the overall size of the facility and quantity of stored flammable/combustible material. The wisest course of action is to provide heat and smoke detectors in each laboratory and provide a sprinkler system at least in the hallways. Each laboratory should have at least one ABC portable fire extinguisher. Computers have become more important to laboratories than ever. Halon fire extinguishing systems are available which are nondestructive to both electronic equipment and human life. These should be employed for fire protection. 

Evans, D. and Stroup, D., Methods to calculate the response time of heat and smoke detectors installed below large unobstructed ceilings. Fire Technology 1986, 22, 54-65. 

Automatic detection of fire is possible with heat and smoke detectors. These are usually installed on the ceilings and at the top of stair wells of buildings because heat and smoke rise. Smoke detectors tend to give a faster response than heat detectors, but whether manual or automatic call points are used, should be determined by their suitability for the particular installation. They should be able to discriminate between a fire and the normal environment in which they are to be installed. 

Radiation detectors generally complement heat and smoke detectors, especially in tall, unobstructed compartments and are effective in special applications such as flammable liquid storage areas. 

Normal heat and smoke detectors rely on the presence of convection currents caused by the fire to carry either the products of combustion or heat past the detector which is usually mounted at high level. If there is little heat from the fire then there can be a significant delay before the detector receives enough information from the fire to actuate the alarm. Carbon monoxide detectors overcome this problem since the carbon monoxide produced by the fire dissipates into the atmosphere of the protected area and... 

When dealing with an entire fire detection system that utilizes more than one type of detector, a Detonator Module greatly expands the flexibility and capability of the system. An individual Detonator Module can accept multiple inputs from UV and IR controllers, other Detonator Modules, manual alarm stations, heat sensors, smoke detectors or any contact closure device. In the event of a fire, any of these devices will cause the internal fire circuitry of the module to activate the detonator circuit, sound alarms, and identify the zone that detected the fire. When properly used, a Detonator Module will add only one millisecond to the total system response time. See Figure 8 for an illustration of a fire detection system with a Detonator Module. 

A device for the detection and notification of a fire event. Fire alarms can be activated by people or antomatic devices that can detect the presence of fire. These include heat-sensitive devices, which are activated if a specific temperature is reached a rate-of-rise heat detector, which is triggered either by a quick or a gradual escalation of temperature and smoke detectors, which sense changes cansed by the presence of smoke, in the intensity of light, in the refraction of light, or in the ionization of air. The arrangement and type of fire detectors for optimum performance is usually specified by fire codes or industry guidelines. 

All systems should receive a visual inspection each quarter. Test or inspect each antomatic system on an annual basis. Include all systems in the preventive maintenance plan. Test all snpervisory signal devices except valve tamper switches on a quarterly basis. Test valve tamper switches and water flow devices semiannually. Test duct detectors, electromechanical releasing devices, heat detectors, manual fire alarm boxes, and smoke detectors on a semiannual basis. Test occupant alarm notification devices to inclnde andible and visible devices at least annually. Maintain appropriate documentation on all tire-related system testing. 

Four types of sprinkler systems are available wet-pipe, dry-pipe, alternate and pre-action. A wet-pipe system can only be used in premises not subject to frost or ambient temperatures above 70 C. A dry-pipe system is only suitable in premises subject to continuous temperatures below 0 C or above 70 C. An alternate system which enables either wet or dry operation to be selected is suitable in premises subject to freezing during cold weather. Finally a pre-action system, which is a system with a separate heat or smoke detector that allows water into the sprinkler pipework before the first head operates, should only be used where none of the others is suitable. 

Pre-action sprinkler system - this is a combination of a standard sprinkler system and an independent approved system of heat or smoke detectors installed in the same area as the sprinklers. Like dry pipe systems the pipes are filled with air but water is only let into the pipes when the detector operates. Pre-action systems... 

Various types of detectors that recognize heat and/or smoke utilizing fused bimetallic strips, ionization chambers and the interruption of a light beam by smoke or other combustion products. It is important to select the most appropriate form of detector for the environment. Insurers give a modest discount from premiums if the alarm installation complies with the insurance rules. 

Radioisotopes have important commercial applications. For example, americium-241 is used in smoke detectors. Its role is to ionize any smoke particles, which then allow a current to flow and set off the alarm. Exposure to radiation is also used to sterilize food and inhibit the sprouting of potatoes. Radioisotopes that give off a lot of energy as heat are also used to provide power in remote locations, where refueling of generators is not possible. Unmanned spacecraft, such as Voyager 2, are powered by radiation from plutonium. 

Sprinkler systems are an effective way to contain fires. The system consists of an array of sprinkler heads connected to a water supply. The heads are mounted in a high location (usually near ceilings) and disperse a fine spray of water over an area when activated. The heads are activated by a variety of methods. A common approach activates the heads individually by the melting of a fusible link holding a plug in the head assembly. Once activated, the sprinklers cannot be turned off unless the main water supply is stopped. This approach is called a wet pipe system. These systems are used for storage areas, laboratories, control rooms, and small pilot areas. Another approach activates the entire sprinkler array from a common control point. The control point is connected to an array of heat and/or smoke detectors that start the sprinklers when an abnormal condition is detected. If a fire is detected, the entire sprinkler array within an area... 

Smoke detectors are employed where the type of fire anticipated and equipment protection needs a faster response time than heat detectors. A smoke detector will detect the generation of the invisible and visible products of combustion before temperature changes are sufficient to activate heat detectors. The ability of a smoke detector to sense a fire is dependent on the rise, spread, rate-of-bum, coagulation and air movement of the smoke itself. Where the safety of personnel is a concern, it is crucial to detect a fire incident at its early stages because of the toxic gases, lack of oxygen that may develop, and obscuration of escape routes. Smoke detection systems should be considered when these factors are present. 

Duct detector Is located within the heating and ventilation ducts of the facility. This sensor detects the presence of smoke within the system s return or supply ducts. A sampling tube can be added to the detector to help span the width of the duct. 

Fire detectors generally fall within one of three categories heat, smoke, and flame. Heat detectors work by sensing the heat from a fire. Smoke detectors sense the combustion products from the fire. Flame detectors identify flame by sensing the IR or UV light it emits. 

Smoke detectors are primarily used where smoldering fires can be expected and where electrical equipment is located indoors. Examples of their use are in offices and sleeping quarters, computer rooms, control rooms, electrical switchgear rooms, etc. Their response is typically faster than that of heat detection devices. Smoke detectors are more susceptible to false alarms and usually multiple detectors are required to be in alarm before an extinguishing system is activated. 

A fire occurs in four distinct phases. In the incipient phase, warming causes the emission of invisible but detectable gases. In the second phase, smoldering, smoke is formed so smoke detectors can be used. In the third phase, when the ignition temperature has been reached, flames and their emitted radiation (IR and UV) can be detected. In the fourth and last stage of the fire, heat is released the temperature of the space starts to rise, and the use of thermal sensors becomes feasible. 

In biomedical sensing, some of the solid-state devices based on thermal sensing cannot be used effectively. The reason is that the sensor itself has to be heated or is heated quite hot by catalytic surface reactions. Thus pellistors (oxides with catalytic surfaces and embedded platinum wire thermometer), chemiresistors, and Figaro sensor smoke detectors have not found many biologic applications. 

Smoke detectors are particularly useful in those situations where the fire is likely to generate a substantial amount of smoke before temperature changes are sufficient to actuate a heat detection system and before a fire eye will detect a flame. Smoke detectors use a photoelectric beam between a receiving element and light source. If smoke obscures the beam an alarm is sounded. There are... 

Heat detecting devices faU into two categories those that respond when the detection element reaches a predetermined temperature (fixed-temperature types) and those that respond to an increase in temperature at a rate greater than some predetermined value (rate-of-rise types). The two types can be combined into a single instrument They are generally installed when the use of smoke detectors is not practical, or as a backup to smoke detectors. They are used in the following locations ... 

Are heat/smoke detectors present Yes No El If yes, describe type and location ... 

No heat/smoke detectors are present in the monorail storage holes. Both Building 6596 east high bay and Building 6597 high bay have heat/smoke detectors at the ceiling level. ... 

Heat sensors and/or smoke detectors may be part of the building safety equipment. If designed into the fire alarm system, they may automatically sound an alarm and call the fire department, they may trigger an automatic extinguishing system, or they may only serve as a local alarm. Because laboratory operations may generate heat or vapors, the type and location of the detectors must be carefully evaluated in order to avoid frequent false alarms. 

The consumer market for pollution-detection devices and services is growing rapidly, particularly for interior air. Smoke detectors have become a standard household fixture and GO monitors are recommended for fuel-oil- and gas-heated homes. Testing for formaldehyde, mold, and in some localities radon is often part of building inspections during real estate sales. 

Heat detectors should be sited so that the heat-sensitive element is between 25 and 150 mm below the ceiling or roof. Smoke detectors should normally be fixed in the highest point of, and between 25 and 600mm below, any ceiling or roof. The distance between detector heads should not exceed 12 m in general and 18 m in corridors and they should where possible be fitted 6 m away from walls. 

As indicated above, the spread of fire and smoke can be controlled by both passive and active means. On the one hand, the measures include separation of buildings com-partmentation fire walls fire doors fire and smoke shutters controls on air conditioning and pressurization of critical areas such as stairways and, on the other, detectors and alarms extinguishers hose reels and sprinkler systems. Smoke detectors generally detect fire more quickly than heat detectors. 

---