Gas Chromatograph Piping Leak Explodes in Instrument Room

It is important to understand the requirements and standards associated with safe equipment design (especially electrical equipment containing an internal ignition source with flammable gas) in potentially explosive atmosphere environments. Misinterpretation of requirements and standards can lead to serious consequences. If the application of a standard is not fully understood, it is advisable to contact the author of the standard to remove any misunderstanding and not try to interpret the rules.
Gas detection instrument location is critical to proper functioning. Light gases like hydrogen rise in air, and gas detection needs to be at the high point in the potential source area so that even small leaks can be detected. Various alarm/action thresholds below the lower flammability limit (LFL) of the flammable gas give additional warning of a possible problem in the event of a gas leak. The following is a summary of how equipment involved in this incident should have been installed.
The gas chromatograph should not be installed in a sealed cabinet, but should follow explosive atmosphere design standards to have forced ventilation with a minimum flow rate of 12 times the cabinet volume per hour and to exhaust outside the building. With this change, the analysis room can remain in its current configuration and it does not fall under the explosive atmosphere regulations.
The fixed gas detector must be installed in the cabinet sealed volume, and must comply with explosive atmosphere regulations. The gas detector must be connected to an interlock system and set with two threshold levels; the first at 25% of the LFL (which sends an alarm) and the second at 50% of the LFL (which closes the hydrogen isolation safety valve). For this gas detector, the 100% LFL threshold level is set at 4% hydrogen in air.
To minimize the consequences of a possible leak of hydrogen inside the cabinet, it is recommended that the hydrogen isolation safety valve be installed outside the analysis room.
The explosive atmosphere regulations also require the installation of a door switch that stops the supply of electricity and flammable gases whenever the door is opened (for example, when performing maintenance). This door switch limits the risk of creating an explosive atmosphere in the room that is not regulated under explosive atmosphere standards.