Monitoring Workplace Cotton Dust Concentrations

We are occasionally asked to assist clients in setting up or refining their cotton dust monitoring programs in addition to conducting the surveys. Following is a review of some of the main points regarding monitoring of workplace cotton dust concentrations, as required by the cotton dust standard.

29 CFR 1910.1043(d)(2) "Each employer who has place of employment within the scope … of this section shall conduct monitoring by obtaining measurements which are representative of the exposure of all employees to airborne concentrations of lint-free respirable cotton dust over an eight-hour period."

Representative measurements are more easily determined for work areas where concentrations are consistent throughout. This effect can be seen in the illustration below, which exhibits the difficulties of assigning representative measurements when considerable differences in concentrations are present in a work area. The average of all four monitoring sites is descriptive if workers spend equal times in each area, but for instance would not be representative for workers assigned to work only in the area represented by the highest concentration. Obviously this issue does not arise in areas where cotton dust concentrations are relatively consistent throughout and all below the OSHA PEL.

29 CFR 1910.104(d)(2)…"The sampling program shall include at least one determination during each shift for each work area."

This requirement is the basis for conducting monitoring on each shift. For instance, the reason that employers with 4-12 hour shifts survey over a 48-hr. period as opposed to a 24-hr period, in order to obtain representative monitoring for each shift. (OSHA restated the requirement for monitoring each shift in the preamble to the 1985 Amendments to the Cotton Dust Standard.)

29 CFR 1910.1043 Appendix AI. "Sufficient numbers of 6-hour area samples in each distinct work area in the plant should be collected at locations which provide representative samples of air to which the worker is exposed."

OSHA noted in the 1978 preamble to the Cotton Dust Standard that full-shift samples give more accurate information but because of set-up times the full 8-hours could not be sampled. It is usually possible to sample approximately 7 _ hours of 8-hr shifts, and 11_ hrs of 12-hour shifts, to provide the most representative shift data. This meets general OSHA industrial hygiene guidance for sampling at least 7 hours of an 8-hour shift, and also ensures extended shift results are representative for comparison to reduced PEL values in those OSHA jurisdictions where applicable.

29 CFR 1910.1043 Appendix AII. Sampling Equipment

Accuracy of sampler flow rates and filter weighs, along with representative sampling sites are the critical elements in determining accurate representative cotton dust measurements. Accurate flows are known by verifying each sampler’s flow rate prior to and following the survey. Accurate filter weights are insured by calibration of the weighing balance with NIST or ASTM weights, and tracking of blank filter data as part of the Quality Control Program. (The importance of accuracy in weighing is evident in that an error of 1/10 of a milligram translates to a difference of approximately 30 µg/m³ in the resultant cotton dust concentration, as measured over an 8-hr. shift with a vertical elutriator).

For additional information regarding cotton dust issues, contact James Shelton or Jess Finney at 336-931-0300.

In addition to conducting cotton dust surveys, Workplace Group offers a full range of services such as pulmonary testing and tracking software, respirator fit-testing and medical clearance, real-time dust measurements for trouble shooting dust problems, and ventilation measurements to establish or check ventilation system performance parameters.