False-alarm sources

The infrared (IR) detector is an extremely fast device that is capable of detection times as short as five milliseconds. In the past, infrared detectors have been unsuitable for general applications because of the large number of false alarm sources found in the work place. However, when properly applied in controlled surroundings, they can provide reliable and effective protection. 

The use of two separate electrical or mechanical zones of detectors, both of which must be actuated before the confirmation of a fire or gas detection. For example, the detectors in one zone could all be placed on the north side of a protected area, and positioned to view the protected area looking south, while the detectors in the second zone would be located on the south side and positioned to view the northern area. Requiring both zones to be actuated reduces the probability of a false alarm activated by a false alarm source such as welding operations, from either the north or the south outside the protected area. However this method is not effective if the zone facing away from the source, sees the radiation. Another method of cross zoning is to have one set of detectors cover the area to be protected and another set located to face away from the protected area to intercept external sources of nuisance UV. If welding or lighting should occur outside the protected area, activation of the alarm for the protected area would be inhibited by second... 

The costs of a wrong decision are loss of production, on the one hand, and failure to respond to a real emergency on the other. In order to improve his or her decision basis, the control room worker will usually dispatch others to the source of the emergency signal to declare whether it is spurious (false alarm) or whether it is real, but it is containable without need for depressurizing. This takes up valuable time, during which the situation could escalate dangerously. 

Vibration sensors are similar to break-glass detectors but are fixed to walls and doors against violent attack. The stmcture to which they are fitted must not be subject to vibration from external sources, otherwise false alarms may result. 

Flame detectors alarm at the presence of light from flames usually in the ultraviolet or infared range. The detectors are set to detect the typical light flicker of a flame. They may be equipped with a time delay features to eliminate false alarms from transient flickering light sources. 

A global diagnosis system (i.e., accounting for all the available information sources in a single box) could have been developed. However, modularity would then be very low since adding or removing one information source (e.., one sensor) would break down the overall structure and lead to false alarms or... 

The IR/UV flame detectors are used to sense fires. Flame detectors that use only IR or UV can experience false alarms. The IR/UV detector is designed to recognize a different type of flame signature from the detectors while rejecting common false sources. When the conditions of any one of the several fire conditions are met the detector indicates a fire. IR/UV flame detectors generally have a cone of vision from 60 to 120-degree solid cone field of view. 

PRINCIPLE CHEMICAL SOURCES OF SENSOR FALSE ALARMS... 

The Joint Service Agent Water Monitor (JSAWM) is a funded Department of Defense program that is intended to identify, mature and develop the technology needed for specific and sensitive detection of chemical warfare agents (CWA) in source, treated, stored and distributed water supplies. According to the JSAWM criteria, a successful detection system will function in heterogeneous liquid environments, have less than a 10 minute response time with low false alarms, work in both continuous (on-line monitoring) and batch modes, be portable, small, easy to operate, and have very low power requirements. ... 

Prior to applying the RSVS, disturbances need to be identified correctly (via BESI, for instance) and then RSVS can distinguish whether the disturbance is a sensor malfunction or a process upset. Stork and Kowalski [283] stated that false alarms might lead the RSVS to misdiagnose the source of the disturbance. 

Radioactive source. False alarms to perfume, exhaust paint, additives to diesel fuel. 

Fire eye (infrared) High speed Moderate sensitivity Easy to test manually Moderate cost Affected by temperature Subject to false alarms from the many other sources of IR radiation Outdoors or indoors... 

Technically speaking, any chemical that can be ionized by an ionization source will be detectable by the ion detectors. Some of these ion detectors can provide limited identification of diverse chemicals in an air sample. For instance, ion mobility spectroscopy devices, commonly referred to as IMS detectors, measure the time elapsed for the ionized species under atmospheric pressure to form the ion mobihty spectrum. Thus, compounds can be identified through their respective characteristic mobility. However, because of the nondiscriminatory ionization process, IMS detectors are subject to poteutial interference by other compounds. It is necessary to provide means, such as limiting the number of peaks stored in the library or using more than one peak for substance identification, to improve the detectors identification capability and minimize false alarm potential. 

Identify All Interferents. The type and affect of interferinggases or vapors can also influence the choice of gas detection technology. A gas detector, with an interferent response characteristic similar to Fig. 13, would probably be a poor choice in an area where equipment and other surfaces are wiped down with an isopropyl alcohol solution, and could be the source of frequent false alarms. 

Flame detectors are not affected by airflow characteristics. They are suitable for inside or outside use, but they must be shielded from external sources of ultraviolet or infrared radiation such as welding arcs, lightning, or radiating black bodies such as hot engines or manifolds. Ideally, the fire detection system should have more than one fire eye detecting a fire so that false alarms can be weeded out. Flame detectors can be... 

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