Deciphering Blast Pressure Loads

In this 3-part series, you will learn about deciphering blast pressure loads, how a blast damper functions, and how to properly select & size blast dampers.

Deciphering Blast Pressure Loads
A blast wave is a type of shock wave that is created by a sudden and intense release of energy, such as an explosion.

When an explosion occurs, a large amount of energy in the form of a rapidly expanding sphere of hot gases is released. As the sphere expands, it creates a high-pressure shock wave that travels through the surrounding air, creating a blast wave.

Blast pressure loads can cause significant damage to buildings. The blast pressure load generated by an explosion is composed of two main components: the positive pressure wave, which is generated by the initial blast and pushes outward, and the negative pressure wave, which is generated by the subsequent vacuum created by the blast which pulls inward. Both of these pressure waves can cause damage by inducing shear forces, bending moments, and other stresses.

A blast wave can cause damage in several ways.

• It creates a sudden and powerful change in air pressure (overpressure/underpressure)
  The positive pressure wave (overpressure) can push objects away from the source of the explosion causing them to collide with other objects. The negative pressure wave (under pressure) can cause objects to be pulled toward the explosion and then thrown back.
• It can create a rapid change in temperature
  This can cause thermal damage to objects in its path. The blast wave can heat objects to high temperatures, causing them to melt or vaporize, and can also create rapid temperature changes that can cause objects to fracture or shatter.
• It can generate strong winds
  The wind generated by the blast wave can create shear forces, bending moments, and other types of stresses that can cause structural damage to buildings and other objects.

What types of explosions create blast waves?
There are several types of explosions that can create blast waves including:

• Chemical explosions caused by improper storage or handling of chemicals.
• Gas explosions that occur when a buildup of flammable gas or vapor is ignited.
• Dust explosions from a cloud of combustible dust that is ignited, causing a rapid and intense combustion reaction.
• Munitions explosions

The difference between incident or side-on overpressure and reflected pressure.
Overpressure is the gas pressure above ambient pressure that results from an explosion. How a blast wave (overpressure) interacts with a structure defines the pressure exerted. If the surface of a structure is parallel to the direction of blast wave propagation, the pressure exerted on the target is the incident pressure, or side-on pressure. When a blast wave impacts the surface of a building that is not parallel to the blast wave propagation, the wave reflects and creates a higher pressure, called reflected pressure. Reflected pressure is highest when the reflecting surface is perpendicular to the direction of the blast wave.

Learn more about how a blast damper functions, and how to properly select & size blast dampers.