In most explosions that injure people inside buildings, the blast wave itself is not the main killer. Flying debris is: shattered glass and chunks of wall propelled into occupied space. That is why so much blast mitigation work focuses on keeping walls from breaking apart, or at least catching the pieces when they do.
Why ordinary walls fail
Blast loads are extremely high pressures that last only milliseconds. Unreinforced concrete block and brick walls are strong in compression but weak in tension and bending. Under a blast, they crack, break into fragments and fly inward at high speed. Lightweight walls and cladding can fail in similar ways.
The most effective defense: distance
Blast pressure drops quickly with distance from the explosion. Keeping vehicles and threats away from the building with setbacks, bollards and barriers is the single most effective protection, which is why standoff distance is central to government antiterrorism design standards. Walls are the next line of defense when standoff is limited.
Wall hardening methods
Reinforced concrete and grouted masonry
New construction can use reinforced concrete or fully grouted, reinforced masonry designed for blast loads. Very effective, but hard to retrofit.
Steel stud backup and catch systems
Steel framing or cables behind a masonry wall catch it as it fails and stop debris from entering the room.
Fiber-reinforced polymer
Carbon or glass fiber sheets bonded to the wall add tensile strength and help it flex without shattering.
Sprayed elastomeric coatings
Spray-applied polyurea on the inside face of a masonry wall acts like a tough, stretchy skin. When the wall cracks, the coating stretches, absorbs energy and holds fragments together instead of letting them fly into the room. U.S. military research programs tested this approach extensively, and it has become a well-known retrofit for existing structures because it can be applied quickly without major construction. Products such as ArmorThane’s ArmorBlast are formulated for this role.
Why polyurea works for this
- High elongation lets it stretch far before tearing
- High tensile strength resists rupture
- Fast cure keeps buildings in service during retrofits
- Thin and light compared with structural additions
- Bonds well to properly prepared masonry and concrete
Design matters
A coating’s effectiveness depends on the wall type, the threat, the coating thickness and how it is anchored at the edges. Wall-to-frame connections often decide whether the whole system holds. Blast retrofits should be designed by engineers with blast experience, using tested systems.
Beyond walls
Windows, doors and roofs are also vulnerable. Laminated glazing and anchored frames reduce glass hazards. Similar principles are used in critical infrastructure and containment structures, as covered at Nuclear Containment. For more practical techniques, read our post on effective blast mitigation techniques.
