RESPONDING TO NATURAL GAS EMERGENCIES
1) The vapor pressure of a substance at 100°F is always higher than the vapor pressure at 68°F.
2) Vapor pressures reported in millimeters of mercury (mm Hg) are usually very low pressures. 760 mm Hg. is equivalent to 14.7 psi. or 1 atmosphere. Materials with vapor pressures greater than 760 mm Hg. are usu- ally found as gases.
3) The lower the boiling point of a liquid, the greater vapor pressure at a given tempera- ture.
Vapor Suppression.A physical method of con- finement to reduce or eliminate the vapors em- anating from a spilled or released material. Operationally, it is an offensive technique used to mitigate the evolution of flammable, corro- sive, or toxic vapors and reduce the surface area exposed to the atmosphere. Common ex- amples include the use of firefighting foams and chemical vapor suppressants.
Venting. The controlled release of a liquid or compressed gas to reduce the pressure and di- minish the probability of an explosion. The method of venting will depend upon the na- ture of the hazmat.
Viscosity. Measurement of the thickness of a liquid and its ability to flow. High viscosity liq- uids, such as heavy fuels oils (i.e., #6 fuel oil), must first be heated to increase their fluidity. A low viscosity liquid (e.g., gasoline) will spread like water and increase the size of the hazard area.
Volatility. The ease with which a liquid or solid can pass into the vapor state. The higher a ma- terial’s volatility, the greater its rate of evapo- ration. Vapor pressure is a measure of a liquid’s propensity to evaporate; the higher a liquid’s vapor pressure, the more volatile the material. This is a significant property in that volatile materials will readily disperse and increase the hazard area.
W
Warm Zone. The area where personnel and equipment decontamination and hot zone support takes place. It includes control points for the access corridor and thus assists in re- ducing the spread of contamination. This is also referred to as the “decontamination”, “contamination reduction”, “yellow zone”, “support zone”, or “limited access zone” in other documents.
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