8.2 Blast Mitigation, Ballistic Protection & Hostile Vehicle Mitigation

Quick Answer: Hostile vehicle mitigation is a tested arrest of a defined vehicle mass and speed. Blast work starts with standoff, then glazing and columns. Ballistic listings such as UL 752 protect against bullets, not trucks or shock waves. Decorative bollards that were never crash-tested are landscaping.

PSP candidates are expected to recommend structural measures for three related but distinct problems: a vehicle used as a weapon or as a bomb truck, air-blast and fragments from an explosion, and gunfire at an opening or a guard post. Mixing those problems is how lobbies get pretty posts, how pharmacies get “bulletproof film,” and how a design review fails.

Hostile vehicle mitigation is a line, not a look

Hostile vehicle mitigation (HVM) keeps a vehicle from reaching a standoff line in front of people, glazing, or a critical structural bay. The line can be passive (always in place) or active (opens for authorized vehicles).

Passive tools include engineered bollards, crash-rated walls, berms, ditches, ha-has, sitting walls, and planters when the planter, infill, and foundation are the tested or calculated assembly. Trees and public art help only if a qualified engineer treats them as barriers; a mature oak is not a rating. Active tools include rising bollards, sliding beams, rotating plates, wedges, nets, and crash gates. Active systems need presence detection, traffic signals, emergency-fast-operate logic, trapped-vehicle procedures, snow and debris plans, and a fire-lane story that the fire marshal will accept.

Standoff is the distance from the protected asset to the point where the vehicle is arrested. For a vehicle-borne explosive, blast intensity falls quickly with distance. Cheap land and a competent vehicle line often beat an expensive facade retrofit. For a vehicle-as-weapon attack with no charge, standoff is still the difference between a truck stopping in the plaza and a truck entering the lobby.

What a crash rating means (and what it does not)

Name the families. In U.S. practice, ASTM F2656 is the common crash-test method for perimeter barriers. Older Department of State K-ratings (from the SD-STD-02.01 family) still appear in legacy specifications. Other programs you will see on international or mixed projects include PAS 68 and IWA 14-1. You do not need a bootleg copy of any test table for the exam. You do need to know what the rating is saying.

A rating is a test condition, not a compliment. It combines:

1. Vehicle class / mass — a sedan test does not prove a medium truck will stop.
2. Impact speed — kinetic energy rises with the square of speed, so “it looked stout at 5 mph in the parking lot” is not a 40 or 50 mph condition.
3. Penetration / P-letter or residual penetration — how far the chassis or payload traveled past a datum after impact. A device that stops the cab but lets the cargo reach the revolving door has not protected the asset.
4. The assembly as tested — posts, footing, soil or slab, spacing, and any infill. Change the cage, the depth, the spacing, or the cover and you have a different product.

Historic K-labels are still used in conversation because K12 became shorthand for a heavy vehicle at a high approach speed with limited penetration. Treat that as a reminder of the idea (mass + speed + penetration), not as permission to write “K12” on a decorative sleeve. ASTM F2656-style condition codes make the same idea more explicit by pairing a vehicle/speed condition with a penetration rating. Specify the condition that matches the design-basis vehicle and the remaining distance to the asset. Then specify spacing that denies the design vehicle while still passing pedestrians and mobility devices—often on the order of about three to four feet clear, which is a site and accessibility decision, not a hidden PSP dogma.

The decorative-bollard trap

This is a favorite field failure and a fair exam trap. Decorative bollards—architectural covers, hollow ornamental posts, light-gauge sleeves over unrated pipe, ceramic planters, and “security” posts sold from furniture catalogs—are not HVM until they are tested or engineered for the vehicle condition, including the foundation. Filling a thin sleeve with concrete does not mint a rating. Matching the planter’s soil weight to the test vehicle’s weight does not mint a rating. Painting them yellow does not mint a rating.

If the threat is a slow, angry sedan at a storefront, an engineer may still justify a non-listed but calculated pipe-and-footing layout for a modest speed. That is engineering, with assumptions on paper. If the threat is a medium truck at speed into a crowded plaza, you specify a listed or tested family and you install it the way it was tested. Mixed streetscapes can hide rated cores inside architectural shrouds when the core and footing are the rated article. The shroud is costume; the core is the barrier.

Berms and ditches are honest HVM when the geometry stops the design vehicle. They fail when a winter plow fills the ditch, when a sidewalk is later cut through the berm, or when the slope is gentle enough to climb. Active beams fail when they are left down “for the holiday rush.” Your recommendation includes the operations story.

Blast: standoff, glazing, and progressive collapse awareness

Blast is a charge, a location, and a building response. Security’s first job is to keep the charge away (standoff and HVM) and to keep people out of the worst glass and collapse zones. The structural and facade engineers own member sizes, connections, and tested curtain-wall systems once you have stated the design-basis threat.

Glazing is the urban injury machine in many blast events. Annealed or tempered panes that shatter send fragments across floors. Laminated glass with an adequate interlayer, real bite in the frame, and anchorage that lets the frame stay in the wall is the usual architectural mitigation. Security film can reduce scatter on existing glass and is a legitimate retrofit conversation; it is not a blast-designed facade by itself, especially when edges are floating on the glass instead of anchored into the frame. Do not specify “thicker glass” as a complete blast strategy. Thickness without laminate, frame, and standoff is still a fragment generator.

Progressive collapse is the cascade in which losing one column or bay takes the floors above or beside it. Vehicle bombs and large charges near a street column are one way to start that cascade. PSP-level competence is awareness and siting, not pretending you will design tie forces. You flag critical columns in the drop-off loop, you push the vehicle line out, you avoid putting the truck trap under a transfer girder if you can help it, and you bring a structural engineer in when the design-basis threat can remove a primary member. GSA, DoD, and similar owner standards exist for some occupancies; commercial office buildings still need an honest conversation even when no federal progressive-collapse chapter applies.

Mail rooms, loading docks, underground parking, and air intakes are blast-adjacent spaces. They are not solved with a bollard photo. They need standoff or hardening, glazing choices, and HVAC intake locations that do not gulp a street-side charge.

Ballistic protection is another listing family

UL 752 is the named U.S. family most often used for bullet-resisting equipment: transaction windows, guard booths, doors, and frames. Other ballistic families exist (including NIJ material tests and EN glazing classes on international work). Lower UL 752 levels are commonly used against handgun threats at cash windows and some reception desks. Higher levels address rifle threats at guard houses and overwatch. Do not memorize a bootleg ammunition table for the exam. Know that the listing is for an assembly—glazing, frame, joints, and how it is anchored—and that a rated pane in a weak storefront is not a rated opening.

Ballistic is not blast. A window that stops a bullet can still fail as a blast membrane or as a pry-out forced-entry panel. Ballistic is not HVM. A guard booth listed for rifle fire can still be parked by a truck if the pad sits on the wrong side of the vehicle line. Indoor rifle positions also create ricochet and spall problems; the listing and the room finishes both matter.

On a PSP recommendation, name the threat, name the family, and name the assembly. If the owner wants pretty posts, put rated cores inside them or admit the residual risk.