According to atmospheric dispersion model calculations, what is the minimum relevant time scale for flammability hazards?

The minimum relevant time scale for flammability hazards in atmospheric dispersion modeling is based on the observation that short-duration gas events can lead to significant risk scenarios if they occur within a certain timeframe. A time scale of 20 seconds is established as a critical threshold because it allows for the observation of potential flammability hazards from the release of flammable gases during dispersion.

This duration is significant as it aligns with the time it might take for a gas plume to travel a distance sufficient to reach any ignition triggers or to disperse enough to create a potentially explosive atmosphere. The choice of 20 seconds helps ensure that safety assessments account for rapid dispersion scenarios that could influence emergency response effectiveness or contribute to accident severity.

In contrast, shorter durations like 5 or 10 seconds may not adequately capture the dynamics of flammable dispersion in many scenarios, as they fail to consider the necessary time required for the physical characteristics of the gas cloud to develop and interact with the environment. A longer time frame like 30 seconds, while perhaps safe, extends beyond the minimum threshold required for immediate assessment of flammability hazards, making 20 seconds a more grounded choice for balancing safety and realism in hazard evaluations.