Emergency Response Distance Calculator

The DOT Emergency Response Guidebook (ERG) assigns initial isolation and downwind protective action distances to hazardous materials by class and release scale, and this calculator applies a simplified version of that structure across five common material types and three container sizes -- it is a planning and training reference for quick estimation, not a substitute for looking up the actual ERG guide number and orange-page table for the specific chemical involved in a real incident, since real ERG distances vary by exact substance, not just by broad material category. Two multipliers scale the base distances further: fire involvement multiplies isolation distance by 2.5x, reflecting how combustion products, pressure buildup, and potential container failure dramatically expand the immediate danger zone. Important limitation: this fire multiplier applies only to Initial Isolation, the close-in hot-zone perimeter -- it does NOT extend Protective Action Distance, Evacuation Zone, or Downwind Distance, which in this calculator's model respond only to material type, container size, and time of day, never to fire involvement. Treat those three downwind figures as unadjusted for fire in a real response, and consult the actual ERG orange pages, which do account for fire scenarios more fully.

Separately, nighttime multiplies the protective action (downwind) distance by 2.5x, reflecting how a more stable nighttime atmosphere traps and carries a vapor plume farther before it disperses, compared to daytime atmospheric mixing that breaks a plume up closer to the source. Evacuation zone area is estimated as a circle with radius equal to the protective action distance, and downwind distance extends 1.5x beyond the base protective action distance to account for plume travel along the prevailing wind direction. Always defer to the actual ERG guidebook, the material's SDS, and incident command judgment in a real hazmat response -- this calculator is for training and planning purposes only.