PHLT 8702 Week 4 Sampling Plan Example

Inhalable First, Then Who, When and How Long: A Wood Dust Sampling Plan for Six Task Groups at a Composite Hardwood Furniture Plant

Student Name

Walden University

PHLT 8702: Environmental and Occupational Exposure Measurement and Assessment

Instructor Name

Month Day, Year

Inhalable First, Then Who, When and How Long: A Wood Dust Sampling Plan for Six Task Groups at a Composite Hardwood Furniture Plant

Purpose

The plan will estimate each worker group's long-term mean exposure to inhalable hardwood dust and the variation within and between workers, so that the plant can judge which groups need controls and whether the Week 3 groups hold together. It covers the six groups whose main agent is wood dust; formaldehyde at the panel press is planned separately. The purpose is stated first because, as the Week 1 discussion showed, a sample without a stated question cannot be interpreted later.

The Size Fraction Comes First

Hardwood dust is linked to cancer of the nasal cavity and sinuses, and the particles that matter are those that deposit in the nose and upper airway, many of them large. The relevant fraction is therefore inhalable dust, the particles that enter the nose and mouth during breathing, rather than respirable dust, which reaches the deep lung, or "total" dust, which is defined only by what a particular cassette happens to collect. The traditional 37-millimeter closed-face cassette, the device behind the plant's old area sample, does not follow the inhalable convention well, and side-by-side studies at wood products plants found that it, the IOM inhalable sampler and the Button sampler collect different masses and size distributions of wood dust (Harper et al., 2004). A European collaborative study of personal inhalable samplers found that performance varied among designs and with wind conditions, and that the IOM sampler was among those that matched the inhalable convention reasonably well at low wind speeds typical of indoor work (Kenny et al., 1997). The plan therefore uses IOM inhalable samplers at 2.0 liters per minute with pre-weighed cassettes, analyzed gravimetrically.

Who Is Sampled

Workers within each group are chosen by random draw from the roster, not by supervisors, so that the sample does not lean toward the workers someone believes are most or least exposed. Bench sanders, the largest and least uniform group, receive more workers, and the wide-belt group, with only six members, is sampled in full. Every sampled worker is measured on two days so that day-to-day variation within a worker can be separated from differences between workers, which is the condition for estimating both components (Lyles et al., 1997).

Table 1

Sampling Allocation by Group (Composite Figures)

Note. Composite plant; group F, panel press operators, is planned separately for formaldehyde.

Which Days

Sampling days are drawn at random from production days across six weeks, with the constraint that each worker's two days fall at least a week apart. Random days prevent the common habit of sampling only on "normal" or "bad" days, either of which biases the estimate of the long-term mean (Rappaport, 1991). If a drawn day turns out to be a shutdown or a day the worker is absent, the next scheduled production day for that worker is used and the substitution is recorded.

How Long

Each sample runs for the full shift, about seven and a half hours, with the pump started at clock-in and stopped at clock-out, including breaks. Full-shift sampling matches the averaging time of the plant's comparison limits and avoids the need to assume that unsampled periods resembled sampled ones. For the cleanup crew, whose peak exposure falls in the last two hours, a second short sample covering the blow-down period alone will be collected on one of the two days, so that the peak can be described separately from the shift average.

What Is Recorded Alongside Each Sample

Each sample carries a short form completed by the hygienist: the tasks performed, the machines used, whether local exhaust was operating, the species and moisture of the wood, unusual events and the start and stop times and flows. Kromhout et al. (1993) found that day-to-day variation is greater where local exhaust is absent or processes are intermittent, so recording exhaust status and task changes will help explain any outlying result rather than discarding it.

How the Results Will Be Used

Results will be log-transformed and analyzed with a one-way random-effects model for each group, giving the group mean, the within-worker and between-worker variance components and the probability that a randomly chosen worker's long-term mean exceeds the comparison limit (Lyles et al., 1997). Groups with large between-worker variance will be examined for subgroups; groups with nearly identical results may be merged.

Telling Workers What Is Happening

Before sampling begins, the hygienist will explain the program at each shift's safety meeting: why some workers are chosen and others are not, that selection is random and not a sign of suspicion, how to wear the sampler and what to do if it is knocked loose. Workers may decline to wear a pump, and a declining worker will be replaced by the next name drawn, with the refusal recorded so that a pattern of refusals can be noticed. Each sampled worker will receive their own results in writing, with the group result for comparison, within two weeks of the laboratory report. Workers who understand the purpose are more likely to work normally on sampling days, which protects the results from the bias of unusually careful behavior.

Limits of the Plan

Two days per worker gives a rough estimate of within-worker variation, and six weeks may miss seasonal differences in wood moisture and production mix. The plan accepts these limits for the first round and will revisit them once the variance components are known, adjusting the number of workers and days in each group to match what the first round reveals.

References

Harper, M., Akbar, M. Z., & Andrew, M. E. (2004). Comparison of wood-dust aerosol size-distributions collected by air samplers. Journal of Environmental Monitoring, 6(1), 18-22. https://doi.org/10.1039/b312883k

Kenny, L. C., Aitken, R., Chalmers, C., Fabriès, J. F., Gonzalez-Fernandez, E., Kromhout, H., Lidén, G., Mark, D., Riediger, G., & Prodi, V. (1997). A collaborative European study of personal inhalable aerosol sampler performance. Annals of Occupational Hygiene, 41(2), 135-153. https://doi.org/10.1016/S0003-4878(96)00034-8

Kromhout, H., Symanski, E., & Rappaport, S. M. (1993). A comprehensive evaluation of within- and between-worker components of occupational exposure to chemical agents. Annals of Occupational Hygiene, 37(3), 253-270. https://doi.org/10.1093/annhyg/37.3.253

Lyles, R. H., Kupper, L. L., & Rappaport, S. M. (1997). Assessing regulatory compliance of occupational exposures via the balanced one-way random effects ANOVA model. Journal of Agricultural, Biological, and Environmental Statistics, 2(1), 64-86. https://doi.org/10.2307/1400641

Rappaport, S. M. (1991). Assessment of long-term exposures to toxic substances in air. Annals of Occupational Hygiene, 35(1), 61-121. https://doi.org/10.1093/annhyg/35.1.61