[Process Safety 2026] Is it necessary to install toxic gas detectors in the dichloromethane storage area?
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This post was last edited by The one on 2026-5-19 13:49. To determine whether a toxic gas detector is necessary for a dichloromethane storage tank, it is necessary to strictly follow the requirements of the \"Design Standards for Detection and Alarm of Flammable and Toxic Gases in Petrochemical Industries\" (GB/T 50493-2019). The specific requirements are as follows:
Firstly, dichloromethane was not found among the 54 substances listed in the \"Catalogue of Highly Toxic Substances\" (Document No. Wei Fa Jian Fa 142). Furthermore, the maximum values for the MAC (Maximum Allowable Concentration of toxic substances in workplace air), PC-TWA (Time-Weighted Average Allowable Concentration of toxic substances in workplace air), and PC-STEL (Short-Term Exposure Allowable Concentration of toxic substances in workplace air) among the substances listed in the catalog are the PC-STEL values for ammonia and carbon monoxide, both of which are 30. The PC-TWA for dichloromethane has already reached 200 mg/m3; therefore, according to the identification results in the \"Catalogue of Highly Toxic Substances\" (Document No. Wei Fa Jian Fa 142), it is not necessary to install toxic gas detectors in the dichloromethane storage area.
Secondly, look at the classification criteria for Category 1 and Category 2 in \"Specifications for the Classification and Labelling of Chemicals – Part 18: Acute Toxicity\" GB 30000.18-2013:
The MSDS for dichloromethane was queried, and the results are as follows:
The acute oral toxicity value for dichloromethane is 1600, placing it in Category 4; it does not belong to Categories 1 or 2. Therefore, in accordance with the \"Specifications for the Classification and Labelling of Chemicals – Part 18: Acute Toxicity\" (GB 30000.18-2013), it is not necessary to install toxic gas detectors in the dichloromethane storage area.
Third, let’s take a look at the requirements regarding the installation of toxic gas detectors as specified in the \"Specifications for the Installation of Toxic Gas Detection and Alarm Devices in Workplaces\" (GBZ/T 223--2009):
Based on the operating conditions of the dichloromethane storage area, it is impossible for this area to release \"highly toxic or extremely toxic\" gases. In the event of a leak, the boiling point of dichloromethane is 39.8°C and its vapor pressure is 46.5 kPa at 20°C, which is not very high; therefore, the conditions for \"possible large-scale release or easy accumulation\" are not met. Therefore, in accordance with the requirements of Article 4.1.1 of the \"Specifications for the Installation of Toxic Gas Detection and Alarm Devices in Workplaces\" (GBZ/T 223--2009), there is no need to install a toxic gas detector for dichloromethane as well.
Finally, we identified the chemical hazardous gases listed in \"Occupational Exposure Limits for Hazardous Factors in the Workplace – Part 1: Chemical Hazardous Factors\" (GBZ 2.1-2019). As a result, we found dichloromethane in Table 1:
Therefore, dichloromethane is one of the 339 common chemical hazardous gases listed in the current **Occupational Health Standards: Occupational Exposure Limits for Hazardous Factors in the Workplace – Part 1: Chemical Hazardous Factors». Thus, strictly speaking, toxic gas detectors should be installed in areas where dichloromethane is stored.
The following are some screenshots from the \"Code for the Installation of Toxic Gas Detection and Alarm Devices in Workplaces\" GBZ/T 223-2009.