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B. CONTAINMENT is defined as those methods used to restrict the material to its original container. Until the released materials are contained, the area of involvement will grow larger, and cleanup will become correspondingly more difficult. Whenever possible, it is important to contain the materials in order to limit the size of the area involved and minimize cleanup difficulties. 2 . CONFINING HAZARDOUS MATERIAL RELEASES Techniques for confining hazardous materials depend upon whether the release is into the air, on land, into surface waters, or into the groundwater. A. Air Releases Releases of gas, vapors, or particulates into air present a serious threat (depending particularly on the identity and quantity of chemical released) . Once in the air, the material can move rapidly depending on wind and other weather conditions, and therefore has the capability of affecting a large physical area. The cloud of material produced may be flammable, toxic, corrosive, or have other hazardous properties. Controlling airborne materials is very difficult especially if large quantities are involved. The first step is to determine if it is possible to prevent or reduce the amount of materials from becoming airborne by containing or confining it. If this cannot be done then some vapor suppression or dispersion techniques may work depending on the quantity being released. Weather conditions such as humidity, temperature, and wind speed and direction can greatly affect cloud formation and dispersion. If the cloud is large, then initial consideration must be given to immediately evacuating the area which has the potential for being impacted. With some materials the use of fog patterns to disperse the vapor cloud can work. When a fog stream is used, the material is condensed and a collecting area such as a dike should be used to capture the water. This collected material should be pumped into a container and disposed of properly. Responders must also be certain that the liquid does not revolatilize (Figure 1) . This use of fog patterns to disperse a vapor cloud should be used judiciously because extensive groundwater contamination as well as excessive cleanup costs can be associated with this method. Air releases or suspected air releases should always be cautiously approached from the upwind direction whenever possible. Personnel must also be on the alert for changes in wind direction. Visual observations or direct-reading instruments may give some indication of the type and quantities of materials being released, and whether vapor suppression will work. 55 Site Safety t Health Plan Rev./1.0 October 20, 1997