In high-risk industries such as petrochemicals, explosion-proof control rooms are critical barriers to ensure the safety of personnel and equipment. However, a seemingly basic question—how should instrumentation cables be introduced into these rooms—has sparked considerable debate in design practices. What do the regulations say about this? Beyond the controversial approaches, are there more standard and reliable solutions? This article explores the relevant standards to provide clarity.
Are There Violations of Standards in the Design?
There are two differing opinions:
Non-compliant design: It is considered non-compliant because explosion-proof walls should not have openings. This contradicts section 4.1.6 of the Petrochemical Control Room Explosion-Proof Design Code GB50779-2012.
Compliant design: It is argued that no violation occurs, as the regulation prohibits openings in the outer walls above the cabinet room floor, but the opening in question is below the floor level.
How Should Instrumentation Cable Entrances Be Configured in Explosion-Proof Control Rooms?
According to the Petrochemical Control Room Design Code SH/T3006-2012:
Preferred method: Cables should ideally enter through an overhead line system. The cable entry point should be sealed with a specialized cable seal module that meets explosion-proof, fire-proof, water-proof, and dust-proof requirements.
Alternative method: When overhead entry is not possible or practical, a cable trench can be used, provided that:
The bottom of the cable hole is at least 0.3 meters higher than the outdoor trench floor and is sealed with waterproof measures. Drainage facilities should also be in place for the trench.
Protection bunds should be set up around the cable entry points outdoors.
Explosion-Proof Control Room Cable Entry Regulations:
The Petrochemical Control Room Explosion-Proof Design Code GB50779-2012 specifies:
Cables entering the room from outside should pass through a cable trench filled with sand. No holes should be made in the external wall above the floor level inside the control room. Any holes in the foundation wall should be sealed with fire-resistant materials.
This is to prevent overpressure from explosions from passing through cable trays or holes in the external walls into the control room.
There must be a height difference of no less than 600mm between the indoor and outdoor ground levels, with a minimum of 300mm between the floor of the raised floor system and the outdoor ground level.
This ensures that any potential external threats, like flooding, do not enter through the cable entry points.
Proposed Solutions for Instrumentation Cable Entry:
Based on the relevant standards in Petrochemical Control Room Design Code SH/T3006 and Explosion-Proof Design Code GB50779, the following two methods for instrumentation cable entry are recommended:
Solution 1: “Sandpit + Explosion-Proof Bund” Approach:
Cables enter the control room overhead, with the cable entry point located between the raised floor and the outdoor ground level. The bottom of the cable hole should be at least 0.3 meters higher than the outdoor trench.
The cable entry point should be sealed with fire-resistant, explosion-proof, water-proof, and dust-proof materials.
An explosion-proof bund should be placed at the cable entry point outdoors, with a drainage system in place. After the cable is laid, the bund should be filled with sand for explosion isolation.
Solution 2: Explosion-Proof Sealing Module Entry:
Similar to the first solution, cables enter overhead with the entry point located between the raised floor and the outdoor ground level. The cable hole should be sealed with an explosion-proof sealing module.