Installation plan for combustible gas detectors
Thread Content
There is an industrial material drying line, a confined space with negative pressure; the ambient gases consist mainly of air and toluene vapor, the temperature ranges from 40 to 120 degrees, and the gases contain trace amounts of silicon. A combustible gas alarm device needs to be installed in this space; what type of sensor should be used? The demand is very high.
This post was last edited by GeniusTTUV on 2022-7-4 18:03:111111
This post was last edited by GeniusTTUV on 2022-7-4 18:04:2222222
This post was last edited by GeniusTTUV on 2022-7-4 18:04, 333333 times
Typical catalytic combustion gas detectors are installed in environments with temperatures not exceeding 70°C; here, the temperature reaches up to 120°C, making detection difficult. Trace amounts of silicon powder can be ignored. You can consult the manufacturer to find out whether the probe can withstand such temperatures, and consider using a split design with the display mounted on the outside.
When I saw the question, my first thought was that a gas detector would be necessary. First of all, toluene is not listed in GBT50493 nor in the catalog of highly toxic substances; however, it falls under inhalation category 1 according to GB30000.18. Therefore, if a gas detector is to be used, it should be a toxic gas detector. Of course, if one insists on the fact that it’s not listed in the first two documents, then a toxic gas detector may not be necessary. One can refer to the explanatory notes in GB50493 or ask the editorial committee for an interpretation. Secondly, as for how to proceed, we need to refer to GBT50493 and GB50058 to examine the environment and emission sources. For closed-negative-pressure production lines, pressure control or interlocks should be in place. Of course, if gas concentration analysis is required, specialized analyzers are needed. In my opinion, there is no need to install toxic gas detectors in the production line (combustible gases only need to be monitored in Zone 2), but detectors must be installed at the locations specified by the regulations as sources of release. Again, it is necessary to determine whether the leakage level can reach the alarm threshold (in most cases, it does). If it does, for toluene, both electrochemical and photoionization methods should work (it is necessary to confirm this with the manufacturer)
Item 30 in Appendix A under combustible gases is toluene; don’t focus on the toxic aspects.
………… If a gas is both toxic and flammable, should it be classified as flammable or toxic? Flammability is indicated by %LEL, which is a percentage value, while toxicity is indicated by %OEL, which is a ppm value. For a single gas, which value should be used? For mixed gases, it is generally sufficient to refer to the concentration in parts per thousand; one value is multiplied by 10^-2 and the other by 10^-6, so it’s easy to see which value is smaller. Definitions and requirements are specified in GB/T50493
It must be a combustible gas alarm; at temperatures of 40-120 degrees, who could get poisoned in there? There is air in the space, along with toluene vapor, and the temperature is high; therefore, a flammable gas alarm is necessary.
This post was last edited by ssln123 on 2022-1-22 08:05. In our area, first-class design institutes classify toluene as a flammable substance, while benzene is classified as a toxic substance; one of these classifications has to be chosen. GBT50493 falls under the category of flammable materials, so it is feasible to configure it as such.
The GB50493-2019 standard has been updated