2nd Key: Understanding the Function

What is the purpose of a blast damper?

A blast damper is a safety device installed in the exterior walls or other wall penetrations of a building to reduce the impact of an explosion by reflecting the energy of the shock wave away. The purpose of a blast damper is to prevent damage to equipment inside a building, protect occupants from injury, and reduce the risk of secondary explosions caused by the initial blast. They are typically installed in HVAC systems, or other openings in a building, that could potentially allow the blast wave to enter.

What are typical applications?

Blast dampers can be used in any application where the risk of an explosion is present and there is a need to protect people and property from the damaging effects of a blast wave. Some typical applications include:

• Industrial facilities such as petrochemical plants, refineries, and storage facilities that house/store explosive materials
• Military installations including ammunition depots, military bases, and other facilities that store or use explosive materials
• Critical infrastructure like power plants, water treatment facilities, and transportation hubs
• Commercial buildings including office buildings and shopping malls (to protect occupants and reduce the risk of property damage in the event of an explosion)
• Government buildings including courthouses, embassies, and other facilities that may be at risk of terrorist attacks or other forms of violence

What determines damper closing time?

It must first be noted that a blast damper cannot prevent 100% of a blast wave from passing through. Damper closing time does impact pass-through leakage, however, closing time cannot be specified as a performance requirement without understanding the variables that influence closing time.

The closing time of a blast damper is determined primarily by three factors:

• Damper Blade Angle – Blast dampers are typically installed with the damper blades in the open position to allow airflow through the damper or to provide ventilation. The angle of the blades in the open position has a direct impact on damper closing time. The less open the damper blades are, the shorter the damper closing time will be for a given blast load. However, a less open blade angle decreases damper-free area resulting in greater pressure drop.
• Blast Load – A higher pressure blast wave will force the damper blades to close faster than a low pressure blast wave.
• Damper Design & Construction – A poorly designed or fabricated blast damper may not close smoothly thereby increasing damper closing time. Design variations aimed at improving damper closing time or reducing pass through leakage (e.g. baffling) will typically lead to much higher pressure drop performance.

Although damper closing time is important, one must be careful when attempting to specify it as a performance criterion as it may become arbitrary. Consideration should be given to all performance needs required in the application.

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