【 Weak current College 】 fire detectors in the false alarm status and causes

Automatic fire alarm system is running, there is a false positive, cause there are many reasons for the
. This article in respect of fire detectors of false alarms cause some discussion.
First, the false alarm and status
1. definition of false alarms and false alarm rate
According to China's national standards, the definition of a false alarm: actually no fire, but fire alarm equipment issued a fire alarm signal. According to international standards, the false alarm is defined as the reported of fire now does not exist, and they never existed. Cause false alarms due to deliberate the malfunction for, or casual factors. Combine the understanding that neither detectors reasons, as long as there is no fire is reported to the fire,
Call false alarms. While false alarm rate is the fire alarm system of the device to be used under the conditions and time limits in the number of false alarms. Usually expressed in millions of hours of false alarm times said: false alarm rate = false alarm times/million hour (106 hours).
2. false alarm of serious harm
People care about false alarms on important public resources resulting in significant losses. For example, the United Kingdom each year, fire alarm equipment failure caused by false alarm fire consuming human and material value more than 1900 million pounds. In addition, false alarms cause workers from their jobs, so that the production is stopped, this loss estimates there will be millions of pounds, it is evident that the seriousness of the problem.
More heavy price is not yet on the economy. United States Institute of standards technology (NIST) is a senior research engineer RichardBukowski said that the cost of false alarms is enormous. Apart from economic losses including time waste, fuel consumption, fire-fighting equipment depreciation, I'm afraid there is a price is greater than the other costs, that is a false alarm enable people lost to fires and sense of urgency, such as the United States air force recently found the pilot received the fire has 3/4 is a false alarm. It was nothing, but further investigation found that 55% of the real fire has been detected, because pilots hate false alarm, the detector connection to disconnect. The air force, is a big problem.
United States from 1974 legislation, household fire detectors has now spread to 93%, according to the 1992 United States consumer product safety Commission survey, there are 1/5 no battery and battery, which is due to false alarms, users who wish to remove the battery, or not to replace the battery. In 1997, the NFPA's previous survey results is 39% of respondents said their detectors in the past year at least 1 time a false alarm, but the seriousness of the problem is that only 7% of people believe that fire is about to occur, you should immediately evacuated, others do not believe that a fire, ignore the alarm signal. This shows that the fire detector harmfulness of false alarms.
3. current problems of false alarms
Since the inception of fire detector, industry has always been the false alarm as a focus of attention. Each detector manufacturers face two requirements: firstly, their products in a timely manner or as soon as possible a real fire; the second, no false alarms. But as the result of false alarms is complex, with the product and use that to achieve these two requirements are often not possible. Even if you only consider product reasons, due to technical restrictions and the level of prices and other factors, to achieve the total elimination of false alarm is also very difficult.
Although completely eliminate false alarms is not possible, but the industry over the years efforts are greatly reduced the rate of false alarms. 1989 United States in a survey, the false positive and real alarm ratio is 15.8: 1; United Kingdom 1988 published a survey reported that the ratio of 20: 1. Since the analog system after local statistics, this proportion can be reduced to 3: 1. Domestic product through a mandatory certification system in recent years, the implementation of ISO9001 and ISO9002 standard, due to the product caused by false alarm is declining, a product is said to have reached the false alarm rate (1-3) * 106.
II. origin of false alarms
Cause false alarms due to very complex, roughly divided into 7 categories:
1. the non-fire soot factors
1.1 cooking oil. According to incomplete statistics, the United States domestic smoke detector 1/3 false alarms caused by cooking oil. In the United States due to the popularity of household fire detectors, ionic earlier smoke detectors to cooking oil is very sensitive, if the source from the fumes from proximity (e.g. inadequate 1.7 m), the false alarm will occur from time to time, such as the popular household smoke detector, because of the characteristics of Chinese cooking, cooking oil
Tobacco induced false alarms are more serious.
1.2 smoking. Cigarette smoke and fire smoke in grain spectrum characteristics on very close, smoke detector especially conventional detector is very difficult to identify, often cause false alarms. This situation in the country, so the domestic smoke detector sensitivity tends to be low in order to reduce the use of false alarms. 1.3 steam. From bathroom to steam is European and American household smoke detector another false alarm.
1.4 dust. Clean the room caused by dust, road dust blowing breeze can result in smoke detector
False alarm.
1.5 insecticides. Aerosol insecticides and air fresheners may trigger a false alarm.
In addition, welding fumes may trigger a false alarm, the combustion of waste paper in the room is also extremely easy to cause false alarms.
2. environmental factors
2.1 electromagnetic environment. Electromagnetic environmental effects of the smoke detector mainly in three ways: air wave interference, power and other input output line narrow pulse group as well as the human body static electricity. Since 1994, the requirements for fire detectors must reach the national standard of the 1993 edition of the three requirements for electromagnetic compatibility, it should be noted that, since the electromagnetic environment is deteriorating, product even if adopted in 1993, is not equal to actual use
Without any problems. In response, some manufacturers at home and abroad is to ownProduct sets a higher standard, for example, some companies for their own detector set up as high as 30-50V/m2GHz em radiation.
2.2 airflow. Flow on effect of ionic smoke detector is well known. However, because the structure of ionic detectors, and photoelectric detector using increasingly broad, because the air flow caused by false alarm is declining.
2.3 dramatic changes in temperature. The use of air conditioning and heating equipment, if the air blowing directly with a sensor elements probes (thermal detectors and composite detector) may cause false alarms.
3. the products to the reasons
3.1 design quality: fault-tolerant, tolerance and environmental sensitivity
The so-called fault-tolerant, mainly refers to the system software in a known and unpredictable accidents by maintaining the ability to run properly. The so-called tolerance, mainly refers to the system hardware parameters of the members of a large discreteness, System properties remain unchanged. The so-called environmental sensitivity, refers to the system in national provisions and the actual use of the potential of mechanical, weather, electromagnetic environment condition remained stable running ability.
Because the domestic detector manufacturers smaller, funds not enough rich, professional experience is not rich, and so on, so the above three areas of significant weaknesses.
3.2 manufacturing quality
Hand job, in the future. From welding to debug into finished products in every aspect, a large number of manual operations, the number of errors and vulnerabilities far exceed automated production. Over the past few years, larger, stronger enterprise is gradually eliminated manual operation, to ensure that quality plays a great role.
"Three" processing in the southern China is using the environment. Adoption of national standards require 92% RH40 ℃, 96-hour test of products does not mean that the South China will be able to stable operation, which
Are mainly manufacturers on "three" with no effort. It should be noted that the aforementioned provision of the national standards is targeted at the General conditions of use, if you want to the rainy season in the South and humid environment long run properly, the product of the capacity of the "three" must be higher than the national standard of the above provisions.
Material control requirements of ISO9001 from significant gap, making the product appear in actual use false alarm or other problems, this phenomenon to thoroughly address, you must do a lot of truly careful work.
4. human factors
4.1 hoaxes and "good for the play". It was deliberate on the smoke detector smoke, or deliberately initiate manual alarm button, causing a false alarm. There is also the observation of judgment is wrong, in good faith to start a manual alarm button, causing a false alarm.
Non-compliance with rules 4.2. For example, smoking in no smoking areas in the Office or room to cook food.
5. engineering design reasons
Have a good product, if you do not have the correct project design, also frequently appears false alarms. NFPA fire research and Analysis Division of john.r.hall think in adopting the new technology of today, the number of false alarms on the rise is mainly due to engineering and technical personnel quality is not high. In 1992, the United States only 50 individuals access to national engineering technology person card association registration, although 1998 has reached 4000 people, but still cannot satisfy the need.
5.1 set location. United States as the cooking of household detector false alarm mainly due to the design-time detector location not far from the source of cooking oil. Also found in boiling water equipment parts installed smoke detectors to throw instances of false alarms.
5.2 improper selection. Smoke detector in normal circumstances dust shall not apply to the site, such as a building's garage and smoking room selection a smoke detector, improper belonging to selection.
6. construction reasons
6.1 construction process. United States Technical Committee Chairman considers NFPA72NationalFireAlarmCode false alarm of the main reason is the poor quality of installation and construction process pollution. domestic situation more clearly, some of the brutal to the project without law. For example, a city art gallery construction interior trim and fire detection systems at the same time, construction, commissioning and found more than half of the detector is not working, need to be cleaned. Detectors outside protective cover (generally made of red) often give people the illusion that people think that as long as you set it, the construction interior trim will not adversely affect to the detector. In fact, the protective cover of the main function is to prevent accidental mechanical damage and surface contamination, to prevent dust in particular architectural decoration of this long period of dust protection role is limited.
6.2 system grounding neglected, or ground is not up to standard, or no grounding, makes the system vulnerable to electromagnetic interference. Cause false alarms.
6.3 construction poor quality, line insulation is not required, the connector line pressure is bad or wiring is not reasonable.
7. the components aging and dust accumulation and insect invasion
7.1 components aging. From reliability, while at the same time practice has proven, lasting more than 10 years of system components aging induced illnesses including false alarm tends to increase, so the fire community life that probes suitable positioning of 10 years.
7.2 dust accumulation. Foreign statistical said that 60% of false alarms from, dust accumulation.
7.3 insect invasion. According to China's national standards, insect NET should be able to prevent volume 1 mm or more insects. In fact, in the South of China's Jiang, insect NET best longer tight, or else you mite a volume less than 1 mm of insects is extremely easy to access, resulting in false alarms. Japan has tended to reduce the insect NET aperture to 0. 5 mm.
III. concluding remarks
The product causes false alarm, we clearly see that, in order to effectively reduce the false alarm rate, not only of design departments, manufacturers must strive, and users, engineering design and construction, technical supervision departments, government authorities have to work hard. It can be said that this is a huge system engineering, less any efforts do not receive satisfactoryEffect.