Standard setting values for the alarm device
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Hello everyone, benzene is a highly hazardous substance; it is necessary to install benzene alarms in the workshops where benzene is produced. But if a substance contains benzene, is it still necessary to install benzene alarms? For example, gasoline contains benzene. According to the specifications for alarm devices, it can be calculated that if the vaporization of gasoline reaches the explosive threshold, it means the concentration of benzene has exceeded the specified limits; in such cases, a benzene alarm device is necessary. However, I have not heard of any workshops that produce gasoline installing such alarm devices. The situation with H2S is similar as well. I wonder how everyone handles this situation. Is it set based on empirical values? Is this design responsibility in the event of an accident?
It seems that gasoline evaporates more easily than benzene. So, it’s sufficient to install a gasoline alarm
If it were that simple, there would be no need for calculations:'(
The alarms in the units used for producing gasoline are designed to detect combustible gases (the alarm threshold is not the lower explosion limit of gasoline; it is much lower than that limit). The setting for the hydrogen sulfide alarm is also determined according to relevant standards (not exceeding 20 ppm, with an alarm triggered once levels exceed 10 ppm).
You can calculate according to those specifications: before the combustible gas alarm goes off, the benzene concentration had already reached the lower limit set for the benzene alarm. According to the specifications, such a situation requires the installation of a benzene alarm, but none was installed on site.
Alarm devices must be installed in areas with flammable and toxic gases. Document No. 116 has been added to the regulations, carrying the same validity as the regulations themselves. The lower limit for combustible gas alarms is generally set at 25% of the lower limit of the explosive limit
The regulations also require this; you should calculate it based on the benzene content in gasoline first. Check whether the requirements for setting up a benzene alarm have been met.
The calculation you mentioned is now referred to as risk assessment; here it is evaluated based on flammable gases (mixed hydrocarbons), rather than toxic gases.
Has the specification been changed? This project was done last year; I didn’t work on design for a year. I’ll look into it when I have time.