False alarms

Figure 6 Fig 4. part inspection with the new desien ofnhotothermal camera only the crack indications can be seen in spite of the rough surface condition (no more false alarms). 

Please notice that in a well-ventilated laboratory and a pressure cell, these experiments can be executed safely. In seven years of graduate research activity at the Chemical Engineering Department of the University of Akron, only one catalyst ignition and one real CO alarm occurred. Several false CO alarms were sounded until someone noticed that they always happened about 2 30 PM. As it turned out, one maintenance employee parked his old car right in front of the air intake to the lab ventilation. He warmed up his car for a while before he started to go home after his shift, and the motor exhaust gas set off the false alarms. 

During break (approx. 22 30) had been called by control room operator to check separation room as gas alarm had gone off. Operator stated that false alarms are common. 

When high gas alarm went off, he thought it was probably a false alarm, as has happened in the past, especially after work done on pump. Then requested plant operator to investigate. 

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. 

Microwave movement detectors utilize the principle of the Doppler effect on high-frequency low-power radio waves. These units are moderate in cost and suitable for large-volume coverage. Microwaves, however, penetrate certain materials easily, such as plasterboard, and careful siting is required to avoid false alarms. 

A number of alarm systems suffer from repeated false alarms. This may be due to the poor design and selection of detectors, inadequate standards of installation or preventative maintenance, and faulty operation of the system by key holders. Recurrent false calls will quickly discredit any system and may result in the withdrawal of police response to any alarm activation. 

While alarm systems may be complex, false alarms can be minimized by the careful choice of installer, who should ... 

At PicArsn (Ref 19), the fast neutron activation approach for detection of expls in suitcases was extended to the activation of both nitrogen and oxygen using two 7-ray detector stations in sequence. After 14 MeV neutron irradiation, the baggage is first monitored for 6.1 MeV 7-rays from the l60(n,p),6N reaction (7.5 sec half-life), followed by measurement of the 10 min 13N. Because expls are also rich in oxygen and have characteristic ratios of N/O, it was felt that this approach would increase the probability of detection with a corresponding decrease in the false alarm rate... 

Z4. False alarm calls to the emer9enc>( services put lives at risk. ... 

Whilst the emergency services are wasting time on a false call they can not be so readily available to help someone who is genuinely in need of help. Minutes, even seconds, count when someone is in serious need of help. False alarm calls divert these resources. 

Good move - but, if they are simply asleep, a false alarm. 

PFA POD PROACT PROTECT probability of false alarms probability of detection Protective and Response Options for Airport Counter-Terrorism Program for Response Options and Technology Enhancements for Chemical/Biological Terrorism... 

A staggering number of papers are published each year in the literature on various candidate chemical/biological detection systems. Researchers and manufacturers make diverse claims of detection limits, sensitivity, false-alarm rates, and robustness for these systems. The committee believes that in many cases, researchers emphasize the strengths of their particular detection systems while minimizing or ignoring their flaws. This practice makes it virtually impossible to evaluate the likely performance of a detection system in real-world air transportation environments. 

For the detection of slow-acting biological agents (which may not produce symptoms for several days), the system response time would depend on the frequency of sampling and analysis. The frequency of sampling and analysis would be determined by factors such as the cost of the assay, the frequency with which critical reagents need to be replaced, the robustness of the detector, and so on. The minimum response time would be determined by the time required to collect a sample, prepare it for analysis, conduct the assay, and report the results. In the event of an alarm from a detector with a significant false-alarm rate, additional time would be required to determine its validity and to decide on an appropriate response. 

All detection systems feature a trade-off between the probability of detection (POD) of the target substance and the probability of false (positive) alarms (PFA). POD refers to the probability that the instrument will detect a threat material that is present PFA refers to the probability that the instrument will alarm when a threat material is not present at a given threshold level. The overall concentration of the target substance affects this trade-off higher concentrations are easier to detect, resulting in performance closer to the optimum operating point (perfect detection with zero false alarms). In addition, where data are accumulated over time, one can increase POD and decrease PFA by increasing the accumulation time. 

Not rejected Test result OK Error of second kind consumer risk false alarm ... 

Rejected Error of first kind producer risk false alarm Test result OK... 

The property needs to be of a nature that control or background measurements also can be made so that the effects of the pollutant can be precisely determined (4) The property needs to be sensitive enough to indicate pollution but also sufficiently robust not to give false alarms (5) The property needs general scientific validity based upon reliable and... 

Reliability. Sensors must indicate the presence of hydrogen specifically, and not provide false alarms. The sensors should have consistent reproducibility (e.g., 5% over 1 year at 2% v/v H2 in air), long-term stability and minimal drift rates. Response must not drift outside acceptable limits over that lifetime without providing an alarm. Figure 15.3 [3] shows an example comparison of the theoretical versus measured... 

Catalytic bead False alarms from hydrocarbons and volatile organic compounds 500- 4,000... 

---