CBC 414.5.4, exception 4

[earshavewalls]

What qualifies as "an approved fail-safe engineered system"? I cannot find any definition of "fail-safe" in the code.

I have an engineer who is trying to avoid providing emergency power for the mechanical ventilation system for an H-3 occupancy housing Class I-B flammables.

Any guidance here would be appreciated in defining "Fail-safe" for this engineer.

Thanks

 

[Yikes]

Just to clarify, in general "fail-safe" does not mean that a system will never fail. Rather, it means that when it DOES fail, the failure mode results in the safest mode of operation (or non-operation, whatever is safest).

For example, on a traffic signal, failure results in a red flashing light in all directions, forcing everyone to stop. It does not default to green in all directions, because that would mean that no one would stop!

Other examples: most elevators are designed to "fail safe" by lowering to the ground floor.

Magnetic hold-opens "fail safe" during power loss by allowing a fire rated door to default to a closed position, which is the safest postion to prevent spread of fire.

Damaged undersea oil wells fail-safe by shearing closed the... oh, wait...

Hypothetical: if there was a hazardous material where the mechanical ventilation was necessitated by the handling of the material (CBC 414.3) - but not the storage of it - then an alternative to back-up power might be a system that goes into fail-safe mode by removing the hazardous material from the handling system + disabling the handling operation. (Reality is, it's probably easier just ot provide the back-up power.)

BTW, "approved" is defined in CBC 202. A proposed fail-safe system will need the blessing of the Authority Having Jurisdiction.