Overview of solutions
The combustible toxic gas alarm is also known as gas leakage detection alarm. It is a preventive alarm in the regional gas leakage safety monitor. When the combustible gas leaks in industrial environment and daily living environment (such as the place where the natural gas is used) and the combustible gas alarm finds that the combustible gas concentration reaches its preset alarm value, the combustible gas alarm will give the audible and visual alarm signal to remind operators to take personnel evacuation, forced ventilation, activation of shut-off value, spray system and other safety measures. Also, the gas alarm can link with relevant equipment that in case of gas leakage in plant production, storage and transportation it can start ventilation, cut off power supply, activate spray system to avoid the occurrence of explosion, fire and poisoning so as to guarantee safety production. It is often used in chemical plant, petroleum, gas station, iron and steel plant and other places where the combustible gas is used or generated.
Installation of gas detection system
If the new, expanded or reconstructed flammable, explosive and hazardous gas production unit and storage and transportation system are possible to cause accidental leakage of combustible and hazardous gas, the alarm must be provided according to design specification. There shall be gas alarm at the plant corner where there is gas.
The gas alarm shall be installed in the area where there may be gas leakage, and it shall be firmly installed. The installation position shall be dependent upon the specific gravity of detected gas relative to air. When the detected gas has higher specific gravity than air, the gas alarm shall be installed at (30~60) cm above ground; if lower than air, the installation height of the gas alarm is advisable to be higher than the release source by (0.5~2) m. In order to correctly use gas alarm and avoid the occurrence of fault, do not install it at the following places:
a. The place directly exposed to steam and oily fume;
b. The place with large air volume, such as air supply port, exhaust fan and door;
c. The place full of water vapor and water drop (humidity: >93%RH);
d. The place where the temperature is lower than -40℃ or higher than 70℃;
e. The place of strong electromagnetic field;
f. In the environment where there are the following substances:
（1） Silicon-containing compound, such as silane, siloxane, etc.
（2） Sulfur-containing compound, such as hydrogen sulfide;
（3） Phosphorus-containing compound;
（4）Freon, diborane, ethylene glycol, triethylene glycol, germane, arsine, hydrogen chloride, chlorine, phosgene, alkyl naphthalene.
The gas alarm shall be installed at a fixed point and cannot be change once installed. In specific application, the following considerations shall be made.
(1) Make clear the possible leakage points of the monitored device, analyze their leakage pressure, direction and other factors, draw the distribution map of probes, and classify into levels I, II and III based on the severity of leakage.
(2) Based on air flow direction, wind direction and other factors of the place, determine the leakage direction of combustible gas in case of serious leakage.
(3) Based on the density (greater or less than air) of leaked gas and the air flow trend, form a 3D leakage flow trend chart and initially plan the setting points in the downstream of leakage.
(4) Determine whether the leaked point is micro leakage or sprayed leakage. In case of micro leakage, the setting point shall be adjacent to the leaked point. In case of sprayed leakage, the setting point shall be slightly far from the leaked point. Based on these conditions, draw up a final setting point plan. In this way, the quantity and type to be purchased can be estimated.
(5) For the large place where may be leakage of combustible gas, one detection point shall be provided every 10~20m as required. For the unattended small pump room which runs discontinuously, it is necessary to pay attention to the leakage possibility of combustible gas. Generally, one detector shall be installed down the wind.
(6) In the place of hydrogen leakage, the detector shall be installed on a plane above leaked point.
(7) For the gas medium with higher density than air, the detector shall be installed on a plane below leaked point depending on the environment features. For the place where it is easy for accumulation of combustible gas, it is necessary to pay high attention to the setting of safety monitoring point.
(8) In case of the open diffusion of combustible gas, the combustible gas content in air at a point may approach or reach the explosion lower limit concentration due to poor ventilation, so these are monitoring points which cannot be ignored.