Nathaniel Pyron on Explosives Safety Arcs


 On a military installation, some of the most powerful land-use controls are invisible. They are circles — or, more precisely, arcs — drawn around every place explosives are stored, handled, or maintained. These explosives safety quantity-distance arcs dictate where buildings, roads, and people can go, and no installation master plan is credible without them.

Nathaniel Pyron, a military urban planner specializing in military master planning with an airport/airfield focus, considers quantity-distance (QD) planning one of the core competencies of the installation planning profession. Pyron notes that while a civilian planner zones around highways and floodplains, a military planner zones around potential explosion sites — the arcs are non-negotiable, and everything else on the map has to respect them.

What the arcs are

The Department of Defense Explosives Safety Board sets the standards for how far inhabited structures, public routes, and other explosives sites must be from a potential explosion site (PES) — a magazine, an operating building, a holding yard, a pier loading ordnance. The required separation grows with the net explosive weight involved, and it varies by the type of exposed site. Inhabited building distance (IBD) protects barracks, offices, housing, and other places people live and work. Public traffic route (PTR) distance protects roads and rail lines used by the general installation population. Intraline distance (ILD) separates explosives operations from one another so one event does not propagate to the next. Intermagazine distance keeps storage magazines from setting each other off. Draw these distances as radii around every PES and you get the arcs — overlapping footprints that can cover hundreds of acres on an ammunition-heavy installation.

Why planners, not just safety officers, own this

Explosives safety professionals calculate the arcs; planners live with them. Every siting decision on an installation — a new headquarters, a child development center, a parking structure, a runway extension — has to be checked against the QD map. Build inside an arc without authorization and the project stops. That makes the arcs a first-order input to the future land-use plan, the capital investment strategy, and the area development plans. The practical planning moves are straightforward but unforgiving. Map the arcs as a hard constraint layer: QD arcs belong in the GIS alongside floodplains, wetlands, and airfield imaginary surfaces — visible on every siting map from day one, not discovered at 60 percent design. Reserve compatible uses inside arcs: not everything is prohibited within an arc. Open space, certain industrial uses, and low-occupancy facilities may be compatible depending on the arc type. Planners who understand the distinctions can put productive uses on constrained land instead of sterilizing it. Plan for the waivers you cannot avoid: when mission needs collide with QD requirements, installations document explosives safety site plans and, where justified, pursue formal waivers, exemptions, or deviations. Planners should know that process exists — and that it is slow, so it must start early. Guard the arcs against encroachment: like airfield clear zones, QD arcs only work if the land inside them stays controlled. Leasing, outgrants, and adjacent development all need review.

The land-use payoff

Installations that treat QD as a planning input rather than a late-stage veto save years. Projects get sited right the first time, military construction programming reflects real constraints, and safety reviews become confirmations instead of crises. In Pyron's framing, the arcs are the installation telling you where the mission's risk tolerance ends — and a good master plan listens. For communities outside the fence line, QD planning is also a compatibility story. Arcs that extend toward installation boundaries shape what can happen on neighboring land — another reason installation planners and local governments need standing coordination, not just occasional meetings. It is technical, exacting work, and it rarely appears in glossy renderings. But ask any installation planner what actually governs the map, and the arcs are always in the answer.

About the author: Nathaniel Pyron is a military urban planner specializing in military master planning with an airport/airfield focus. He served three years with the United States Marine Corps as a community planner at Camp Blaz and Darwin, Australia, and studied at the Arizona State University School of Urban Planning. Based in Honolulu, Hawaii, he writes about installation planning, airfield land use, and the intersection of military readiness and community design. His LinkedIn title is Urban Planner (Land Use & Airspace).

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