Issues with explosion-proof cabinets for safety barriers at the installation site
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Is it feasible to place the safety barrier in an intrinsically safe explosion-proof cabinet or a flameproof cabinet on-site, with the cabinets located in an explosion-proof area? Is there any evidence?
The explosion-proof cabinet also constitutes a safe area; a safety barrier must be installed between the non-intrinsic safety instruments inside the cabinet and the intrinsic safety instruments in the explosion-proof area.
No, because the safety barrier must be placed in the safe area. For applications requiring intrinsically safe explosion protection, other types of explosion protection are not acceptable.
Isn’t the explosion-proof cabinet considered a safe area? Which specification explicitly states that it’s not allowed?
Positive pressure explosion protection and flame isolation are two forms of explosion protection. Switching power supplies are placed inside the explosion-proof box, so there’s certainly no issue with the safety barriers.
Are explosion-proof cabinets placed in hazardous areas? Even if the area inside the explosion-proof cabinet is considered a safe zone while the area outside it is a hazardous zone, the wires coming from the central control room are also non-intrinsic safety wires. In short, it’s not a viable solution to place the safety barrier in an intrinsically safe cabinet or a flameproof cabinet on site, with those cabinets located in an explosion-proof area! !
This approach is feasible. There is a simple example: a petrochemical plant’s spherical tanks use a radar level gauge manufactured by Emerson. The level gauge itself features an explosion-proof design, but the gauge attached to it for monitoring the liquid level in the tank is of the intrinsically safe type. In this case, a safety barrier is built into the explosion-proof enclosure of the radar level gauge, and the signal passes through this safety barrier before reaching the gauge attached to the tank; this constitutes an intrinsically safe circuit. Meanwhile, the signal sent to the control room does not pass through any safety barrier, relying instead on the explosion-proof design.
Whether it is the control cabinet on-site or the one behind the control room panels, positive pressure ventilation should be ensured as much as possible; this is part of the safety inspections carried out in our organization. I can’t remember which standard requires this
So far, there are no clear guidelines stating whether it’s allowed or not; everyone should be careful.