CFPS Exam Example question - Which of the following statements is true about UV detectors used for fire detection?

 

CFPS Exam Question Example 

Which of the following statements is true about UV detectors used for fire detection?

A) UV detectors are not sensitive to hydrocarbons or metals.

B)  UV detectors are sensitive to all types of fires except hydrocarbons.

C) UV detectors are sensitive to most fires, including hydrocarbons, ammonia, sulfur, hydrogen, hydrazine, and metals

D) UV detectors are not effective in detecting fires caused by middle and heavy fraction petroleum distillates.

Answer: c) UV detectors are sensitive to most fires, including hydrocarbons, ammonia, sulfur, hydrogen, hydrazine, and metals.

SECTION 14 

14-24 SECTION 14 ■ Detection and Alarm

Flame Detectors.

Ultraviolet Flame Detectors. 

The ultraviolet spectrum comprises wavelengths ranging from approximately 0.1µm to 0.35µm.  UV detectors typically use a vacuum photodiode Geiger-Muller tube to detect the ultraviolet radiation that is produced by a flame. The photodiode allows a burst of current to flow for each UV photon that hits the active area of the tube. When the number of current bursts per unit time reaches a set level, the detector initiates an alarm. A special control unit is required to monitor the count rates from UV detectors and initiate alarm.

UV detectors are sensitive to most fires, including hydrocarbons (liquids, gases, and solids), ammonia, sulfur, hydrogen, hydrazine, and metals such as magnesium. However, the smoke produced by combustion of middle and heavy fraction petroleum distillates is highly absorptive in the UV end of the spectrum, and this must be compensated for in system design if UV detectors are used