An otherwise useful chemical may become a villain in an instant simply because it is released to an unprepared environment. The air quality significance of such an event can be profound when air-active chemicals are involved. We can exert little control over the effects of such chemicals on man or environment for some length of time; therefore, what is done or not done by all persons involved during the first 4-6 h is critical. Consequently, how governments, industries, and local communities prepare for the event eventually dictates the outcome in terms of damage and even death.(Author)