Self-inflicted Roof Blow-off

Self-inflicted Roof Blow-off

Moral: Don’t override the safety system. It’s there for a reason.

Situation

We were asked to design a roof replacement for a small building that housed electronic switchgear and computers. The HVAC system was oversized with a backup system, because of the necessity to keep this equipment at its proper operating temperature.

Mistake

The mechanical system operator decided to test the system. In preparation for the test, the pressure relief dampers were blocked off. These dampers were spring loaded and calibrated to vent excess pressure from the building interior in the event of a problem with the HVAC system.

The HVAC system could operate by recirculating the interior air, or by pulling in air from outside the building.

With the relief dampers blocked, the HVAC system was turned on with full outside make-up air.

Result

The rise in the interior air pressure resulted in the roof system being “blown” off the building. It actually did not leave the building, but rose off the deck and came back down when the HVAC was shut off.

Lesson learned

The safety system is there for a reason. Someone has determined the need for the system and designed it for that purpose. The system may be designed for situations that may not be obvious.

Overriding the safety system can lead to unintended consequences.