Alarm values for chlorine and hydrogen fluoride detectors
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I searched through many posts, and different people set different values for the chlorine alarm thresholds; some used around 0.3 ppm, while others used values between 1 ppm and 3 ppm. However, the standard specifies that the maximum allowable concentration (MAC) of chlorine is 1 mg/m3, which is equivalent to 0.3 ppm. Does that mean all values above the 0.3 ppm threshold are not in compliance with the standards? There is also a question regarding the interlock value: should it be higher or lower than the alarm value? Shouldn’t the interlock value be lower than the alarm value? The fan should be turned on for ventilation once the interlock value is reached, in order to prevent it from reaching the alarm value?
2. The alarm set point (upper limit) for toxic gases should be less than or equal to 100% MAC/PC-STEL; when it is difficult to prepare standard gases, the alarm set point may be below 200% MAC/PC-STEL. The alarm setpoint for toxic gases (high and high-high limits) shall not exceed 10% of the IDLH value. 3. The measurement range for toxic gases should be 0～300% MAC or 0～300% PC-STEL ； When the measurement range of the existing detectors cannot meet the above requirements, the measurement range for toxic gases can be 0–30% IDLH ； 4. The high alarm value can be determined by the enterprise after comprehensively considering various on-site factors, such as toxic gases and their toxicity, the condition of personnel, the consequences of accidents, processes and equipment, as well as meteorological conditions. 5. The high-level alarm indicates that a large amount of toxic gas has been released in this area, reaching a dangerous level; it is necessary to promptly activate the emergency response plan, ensure the protection of staff, and evacuate relevant people from the area. Quoted from the \"Design Code for Detection and Alarm of Flammable and Toxic Gases in Petrochemical Industries\", which is the standard with the code GB50493-2009. Generally, the code specifies only the maximum value for the first-level alarm (high alarm); no clear requirements are set for the high-high alarm level. The high-high alarm value can be determined by taking into account various on-site factors such as the type of toxic gas and its toxicity, the presence of personnel, the potential consequences of an accident, the process and equipment in use, as well as weather conditions. Conversion between mass in mg/m3 and volume concentration in ppm: The concentration expressed as the mass of pollutants per cubic meter of air is called mass-volume concentration, with units of milligrams per cubic meter or grams per cubic meter. The conversion relationship to ppm is as follows: X = M.C/22.4; C = 22.4X/M. Here, X represents the concentration of the pollutant in milligrams per cubic meter ； C—Concentration value of pollutants expressed in ppm ； M—the molecular weight of the pollutant. The MAC value for chlorine is 1 mg/M3, with M=71; converting this gives an alarm threshold of no more than 0.32 PPM. Generally, we set the interlock value for fans at 0.32 PPM – this way, the fans will start operating as soon as the MAC value is reached. MAC stands for Maximum Allowable Concentration, which refers to the highest concentration that is permissible
Thank you very much. I would also like to ask whether the interlock value and the alarm value are the same. For example, if the interlock value is 0.32 ppm, what should the alarm value be set at?
According to the specifications, the first-level alarm value should not be higher than MAC, that is, 0.32 ppm
Which manufacturer’s alarm devices have an accuracy of 0–1 ppm, with a setting range of 0.3–0.6 ppm? Could you provide contact information?