The recent explosion in Beirut is shocking and tragic in multiple ways. First and foremost is the human toll: 150 dead and 5,000 injured. A second concern is the devastating cause of the explosion—the mishandling of 2,750 tons of ammonium nitrate stored in a port warehouse, an easily avoidable accident. A third tragedy, meanwhile, has received relatively little attention. Buildings are typically designed to shelter and protect their occupants. Yet in proximity to such a massive detonation, building materials are transformed into dangerous weapons that become the primary cause of injury and death—not the blast itself.
So how might buildings be constructed differently to protect more lives in the event of such a calamity? The best means of protection is to increase what is called the “standoff distance,” or the distance to the source of the blast. In surprise cases like the Beirut detonation, however, the location of the source cannot be predicted. We must therefore focus on the second most effective protection: choosing building materials that can resist explosive force. According to RedGuard, a pre-engineered building manufacturer, the correct term here is “blast-resistant” rather than “blast-proof,” since it is impossible to guarantee zero damage from an explosion.
During a detonation event, materials adjacent to the source (such as the casing of a bomb) are converted into “primary fragments.” In close proximity, this shrapnel is deadly. But for most building occupants, the main concern is the “secondary fragments” generated from the disintegration of building materials themselves in reaction to the shockwave released by an explosion. According to Peter DiMaggio, co-CEO at Thornton Tomasetti, “Most fatalities are not from direct blast loads, but from flying fragments.”
One strategy is to construct a secure building envelope, increasing load resistance and debris containment using enhanced reinforcing. For example, Ducon micro-reinforced concrete systems employ multiple layers of densely spaced “MicroMat” steel reinforcement for increased strength and blast-resistance. The technology is ideal for securing bulk structural concrete as well as concrete used in building façade assemblies, and may be employed in both site-cast and precast applications. Ducon exhibits high ductility and energy-absorption, with a tensile strength of up to 2,000 psi, an elastic modulus of up to 4,600 ksi, and a compressive strength of up to 18,000 ksi. The system may be applied to existing as well as new structures, and the MicroMat’s flexibility and 1/2-inch minimum thickness help facilitate construction.
Another approach is the transformation of multi-material assemblies into tightly interconnected composites. This strategy is exemplified by the SEB-Wall, an enhancement of the conventional cold-formed steel (CFS) stud assembly. Developed by Simpson Gumpertz & Heger, with support from the U.S. Army Research Laboratory, the system uses the inherent lightness and multilayered qualities of the steel stud wall to help resist explosions. Critical augmentations include the use of Sure-Board sheathing panels (sheet steel and reinforced cement board) on both sides of the studs, shear stiffeners, and additional lateral bracing. The resulting composite assembly is ductile, stable, and structurally redundant, with predictable behavior. The advantages of the SEB-Wall include its broad applicability and reasonable cost. According to SGH engineers: “With a total construction cost of $27 per square foot (including materials and labor and excluding architectural finishes), it provides approximately 30% in cost savings in comparison to other high-performance blast-mitigating wall systems, including reinforced concrete, reinforced masonry, and precast/pre-stressed wall panels.”
Glass is another critical consideration, since many explosion-related injuries are due to flying shards from broken windows. Several manufacturers offer blast-resistant glazing, which includes a robust plastic interlayer to hold glass fragments together. Oldcastle BuildingEnvelope offers one such product, and recommends that both inside and outside lites of an insulated glazing unit be laminated to protect against flying shards on both sides of a window. When installed in a blast-resistant framing system with proper anchoring design, the glass is also more likely to be retained within its opening. Dlubak Specialty Glass Corporation also manufactures blast-resistant glazing, and offers lamination options including PVB glass, DuPont SentryGlass & Spall Shield, and glass/polycarbonate laminates. Dlubak’s glazing is also effective against hurricanes, which can bring not only strong winds but also flying debris.
While effective, these blast-resistant technologies increase the cost of a building project. Understandably, not all building owners will choose to include them—particularly in cases like Beirut’s explosion, which would have been difficult, if not impossible, to predict. Once innovations like laminated glass become sufficiently commercialized, however, their cost will decrease. Furthermore, the added safety such a technology offers will shift perceptions of the old standard. In the future, will it ever be desirable to specify non-laminated glass, knowing it can break into deadly fragments?
Over time, building codes have incorporated enhanced protections, especially in municipalities with a higher risk of natural disasters like hurricanes. For example, a study of the South Florida Building Code, which was updated after Hurricane Andrew in 1992, revealed far less damage to buildings caused by subsequent hurricanes. Code improvements added much-needed protections related to wind pressure and flying debris—enhancements that have been recommended for structures in tornado-prone areas as well. With the steady increase in the global frequency of natural disasters and extreme storm events, such code improvements may become more widespread, and may also help minimize the damage caused by unforeseeable industrial accidents.
