Abstract
This study examined the field precision of National Institute for Occupational Safety and Health (NIOSH) Method 3500, also known as chromotropic acid method, in the range of exposures that covers the Occupational Safety and Health Administration (OSHA) permissible exposure limit of 0.75 ppm and the OSHA action level of 0.5 ppm airborne formaldehyde. Using this method, 78 area samples (25 sets of replicate samples) were collected in a workplace and analyzed. The concentrations of formaldehyde ranged from 0.05 to 1.72 ppm with a mean ± standard deviation of 0.95 ± 0.31 ppm. The precision (coefficient of variation, CV) of 25 sets of replicate samples ranged from 0.03 to 0.24 with an overall (pooled) precision of 0.09, which is in agreement with that stated in NIOSH Method 3500. In 68% of replicate samples the precision was equal to or less than 0.09. The relative accuracy of the sampling and analytical procedure used in this study was evaluated by collecting 12 sets of side-by-side replicate samples using both NIOSH Method 3500 and OSHA Method 52. Method 52 was used to determine whether the concentrations of formaldehyde were within the desired range. The overall mean concentrations were 0.98 ± 0.42 for Method 3500 and 0.78 ± 0.28 ppm for Method 52. These were not statistically different. The pooled CVs were 0.114 and 0.076 for Method 3500 and Method 52, respectively.
