Blast-Resistant Glazing Calculator

It means the design case (from Charge Weight and Standoff Distance) requires a single glass ply thicker than the deepest standard option this calculator's table offers (25mm) -- the displayed Glass Ply Thickness does NOT actually meet the blast threat you entered. Ply Thickness Utilization will read above 100% at the same time. Treat this as a signal to specify a custom laminate build-up with a qualified blast consultant, not as a usable recommendation.

Because they come from two unrelated physical processes. Peak Pressure, Scaled Distance, Positive Phase, and Impulse all derive purely from the Hopkinson-Cranz blast-scaling relationship (Z = standoff / charge^(1/3)) -- a function of Charge Weight and Standoff Distance only, describing the shockwave traveling through open air before it ever reaches a wall. Panel Width and Panel Height don't enter that physics at all; a 300mm test coupon and a 3000mm curtain wall panel sitting at the exact same standoff from the exact same charge experience the identical peak reflected pressure. What panel size DOES change is everything downstream of the blast load being applied -- total glass area, and therefore Panel Weight -- once the required ply thickness (driven by that shared, size-independent pressure) gets multiplied across the actual panel footprint.

The pattern isn't a simple "SGP always wins on thickness" story. At this calculator's low-pressure default (~60 kPa) both types land on exactly 1.52mm total (PVB: 2 x 0.76mm, SGP: 1 x 1.52mm). Push into the 100-200 kPa band and PVB jumps to 3 layers (2.28mm) before SGP needs its second layer, so SGP is briefly thicker overall (3.04mm vs 2.28mm) despite needing fewer plies. But keep pushing past 200 kPa and PVB jumps again to 4 layers (3.04mm) while SGP holds at 2 layers (3.04mm) -- the two totals converge back to equal at the high end. So interlayer thickness between PVB and SGP ties at both the low and high ends of the pressure range and only diverges in the middle band, purely because of where each material's layer-count step function happens to land relative to the other's.

Yes, monotonically across Standoff Distance's full 5-500m declared range -- greater standoff always increases Scaled Distance, which always reduces (or at worst holds steady across a standard-ply plateau) Peak Pressure and therefore the required glass ply thickness, GSA Hazard Level, and Ply Thickness Infeasible risk. This is the physical basis for using standoff (bollards, setbacks) as a primary blast mitigation strategy alongside the glazing itself.

It only ever gets worse, never better. Ply Thickness Infeasible never drops from 1 back to 0 as Charge Weight increases across its full 1-10,000 kg declared range, holding standoff fixed. A bigger design-basis threat only ever holds the infeasibility risk steady or raises it, since a larger charge always raises (or at worst plateaus) the required single-ply thickness.