5

• PPM = gases

  mg/m^3 = particulates
• Fibres/cc = fibres
• Variability influenced by

  • Seasonal variability
  • Inter and intra day variability
  • Changes in the process
  • Variations in worker activities
• Population of interest

  • All workers who are affected by the toxicant
• Sample population

  • Select workers from population of interest that you choose to conduct exposure assessment i.e. collect samples
• Use results from sample population to make inferences about the population of interest
• Law of diminishing returns - A certain minimum number of samples is needed to estimate parameters with acceptably small variance (uncertainty)
• Two types of errors

  • Systematic
  • Random
• Systematic errors

  • Are consistent i.e. same direction (always high or low)
  • Not random; it is inherent in a method or is an artifact of the measurement system
• Examples of systematic errors

  • Improper shipment of samples
  • Errors in preparation of standards
  • Contaminated reagents
• Random errors

  • Are uncontrollable and measured by coefficient of variation
• Examples of random errors

  • Random fluctuations in pump flow rate
  • Random variation in physical environment
  • Random analytical errors of instrument
• Not all chemicals have an exposure limit

  In fact, majority of chemicals do not have a listed exposure limit

  Especially carcinogens and sensitizers
• Employ the principle of ALARA - keep exposures As Low As Reasonably Achievable
• With respect to preference of sampling type for determining TWA, they are, in order:

  I. Full period consecutive samples

  II. Full period single sample

  III. Partial period consecutive samples

  IV. Random (grab) samples
• If there is a TWA for an agent but no listed STEL or a C for that agent, exposure shall not exceed the following excursion limits:

  i. Three times the TWA for any period of 30 minutes

  ii. Five times the TWA at any time