Sunday, September 20, 2009

Basic Chemistry for the First In Crews

Responding to day to day emergency incidents can sometimes turn into scenes involving release of hazardous materials. Recognition of these scenes may not always be obvious. Occupancy and location signs such as industrial, commercial or transportation can give clues as to what types and quantities of hazardous materials may be involved. Once on the scene has been isolated, the next step is to try to identify the product or products involved. Communication with property owners, law enforcement and eye witnesses involved can aid in identification. Basic resources such as the Emergency Response Guidebook (ERG) can give important basic information including health and fire precautions and evacuation distances, but are not always chemically specific. Another key component of hazmat determination is basic chemistry of the material that is released.

If the chemical is known, the basic chemistry of the product must be determined and understood. One of the first pieces of information to gather is whether the material is a solid, liquid or gas. By determining the state of matter, the path of exposure can be predicted, monitoring protocol can be established and the proper PPE can be selected. A solid that is spilled will usually stay where it was spilled, with only the weather factors such as wind and rain effecting the spread. Liquids tend to following the contour of the land and takes on the shape of their containers. Gasses want to dispererse or mix with the air and will be effected by wind currents. Gases will be the most mobile of the states of matter.

When dealing with solids, chemical properties of solubility, bulk density and melting point will help to determine if weather factors of rain, wind or temperature will effect the spread. Water is known as the universal solvent. A chemical that is soluble in water will dissolve when exposed to rain. Simply covering the material may allow for isolation until the material can be removed. The bulk density of a product relates how much a known volume of the product weighs, and can be expressed in pounds per cubic feet. For instance, a material such as flour, with a low bulk density, will be easily spread by a light wind. A material such as sand that has a high bulk density, will not. The melting point is the temperature at which a solid will become a liquid. Those substances with low melting points may be solids in the winter, but liquids in the summer. An example of this is water.

For spills involving liquids, land contour may allow the material to run and pool to low places. Chemical properties like solubility, specific gravity, vapor pressure and pH can aid in determining who to mitigate the problem. Solubility, as expressed in percent (%), is the amount of the material that can be dissolved in water. Specific gravity, when compared to water where water is given the value of one, will determine if the material will sink or float with respect to water. A liquid with a specific gravity of less than one will float on water, such as gasoline. Vapor pressure relates to how much vapor will be given off by the liquid from the surface. The larger the surface area of the spill, the greater the potential for vapors to be given off before the spill is mitigated. The pH of a liquid, which is a measure of corrosivity, determines whether the material is an acid or base. This is very important to know prior to monitoring, since corrosive vapors can wreak havoc on sensitive electronic instruments.

Vapor density and flammable range are useful for characterization of spills involving gasses. The vapor density of gases is similar to the specific gravity of liquids, only the comparison is air. Gasses with a vapor density greater than one will sink, where as gases with a vapor density of less than one will rise, with respect to air. Flammable ranges, which can used to characterize the vapors given off from a flammable liquid or a gas. The flammable range is defined as the difference between the upper and lower flammability limits. If the concentration is too lean to burn, it is below the lower limit. If the concentration is too rich to burn, it is above the upper explosive limit.

The chemical characteristics of pH and Flammability can be measured on scene with the appropriate instruments. Other properties such as vapor density, specific gravity and boiling point, to name a few, can be found in resource material such as the NIOSH pocket guide.

Knowing what material you are dealing with and understanding some of the basic chemical properties will enable the first in engine or responders to make a more informed decision as to initial isolation and personal protection.

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