Common Pitfalls of OBRA Studies

Over the last year I have been involved with numerous Occupied Buildings Risk Assessment (OBRA) studies for our distillery clients across Scotland. These have primarily focussed on proposed control room rooms or offices situated in process areas.

While many of these facilities are trying to safely add to existing, and often aged facilities, we do see a number of common pitfalls which could be avoided, or at least have their impact reduced, with early intervention in the concept phase:

• Occupied buildings in process areas not being designed with fire rated walls.

This is a common oversight we have seen recently. Providing fire rated walls for occupied buildings in process areas allows sufficient time for occupants to safely evacuate the area in the event of a pool fire scenario.

• Not enough adequate fire escapes from the occupied buildings being provided.

Consideration should be taken for the number of fire escapes provided in the occupied building, as well as where the fire escapes lead to. At least one fire escape should be provided which allows the occupant to leave without going through the process area and being exposed to thermal radiation. Or if this is not possible, a protected fire escape (with fire rated walls) should be provided through the process area. As per the Chemical Industries Association (CIA) OBRA guidance, emergency exits should not be exposed to radiation levels greater than 6.3 kW/m2 (maximum level of safe escape), which is derived from Eisenberg probit for a 1% fatality for 90 seconds exposure.

• Proposed locations of occupied buildings with respect to the location of the processing area.

In line with the hierarch of controls (eliminate, substitute, engineering controls etc.), occupied buildings such as offices should be located as far away from the hazardous source as possible. However, an argument can be said for a control room as it is deemed necessary to occupy it to run the plant safely.

What challenges have you faced in located new buildings?

Ryan Roche , Process Safety Engineer

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??Process Safety Consulting | Otecsa Consulting