How to Calculate Permissible Exposure Limits

Permissible exposure limits (PEL) are determined by the Occupational Safety and Health Administration. PELs are necessary to keep laborers safe while operating in hazardous conditions. Contact to silica, lead, gasoline or asbestos, for example, can result in harm if humans are over-exposed. PEL is calculated to determine how much of the specified element a laborer can safely be exposed to over a standard eight hour work day.

Things You'll Need

• Laboratory analysis results
• Pencil
• Paper calculator

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Instructions

• 1

  Identify lab analysis results for exposure to dust, for example. Say the dust contains three elements: quartz, cristobalite and tridymite. Write out these numbers in percentages --- the total percentage of each element that makes up 100 percent of the dust.

• 2

  Calculate total PEL. Multiply the smallest amount of the three elements by two. For example: percent of tridymite by two. Multiply the second largest amount of the three elements by two. For example: percent of cristobalite by two. Add the percentage of quartz, the total of the tridymite calculation and the total of the cristobalite calculation. Add the total number by two. Divide the total by 30 --- or number of official hours per week exposed to the substance --- to get your result.

• 3

  Determine the PEL for an extended work day. Divide the total number of microorganisms found in 1 cubic meter of air. Divide the total to this calculation by the number of hours worked in one day to determine the extended PEL.