During initial isolation, what distance is recommended for a gas hazard?

• A. 150
• B. 75
• C. 100
• D. 330

Answer: (D)

Gas releases create vapor clouds that can move rapidly with the wind and may extend well beyond the immediate source. The first action is to set a large, conservative isolation perimeter to protect responders and the public while you gather information. This initial boundary accounts for worst‑case dispersion since you don’t yet have reliable wind data, release strength, or gas density characteristics. It also gives you time to monitor the plume, establish distance from ignition sources if applicable, and implement controls before more precise sizing is possible. Smaller perimeters risk exposing people to the evolving cloud, especially with toxic or flammable gases. As more details come in, you refine and reduce the boundary to a safer, data‑based distance.