Industrial Hygiene Expert Witness and Occupational Exposure Assessment: Reconstructing Historical Workplace Exposures

Industrial hygiene is the science of anticipating, recognizing, evaluating, and controlling workplace exposures to chemical, physical, and biological agents. The single most common error RoseyFields encounters in occupational exposure disputes is the assumption that if a worker’s measured exposures fell at or below the applicable OSHA Permissible Exposure Limit (PEL), that worker was safe. That assumption is wrong. Workers develop serious, sometimes fatal, disease from exposures that never exceeded the PEL — and the reason is not controversial among industrial hygienists. A PEL is a legally enforceable compliance ceiling; it is not a demonstration that the exposure was safe.

RoseyFields and Dr. Paul Rosenfeld evaluate industrial hygiene data from this premise. The governing question is never “did the exposure exceed the PEL,” but “what was the worker’s actual exposure, and what does the health science say about disease at that exposure.” Measured or reconstructed exposures are assessed against current, health-based benchmarks and against the human health-effects literature — not against a compliance threshold that OSHA itself acknowledges is outdated and, in many cases, not protective of worker health.

1. Why Disease Occurs Below the PEL

A worker can be made sick by an exposure that never exceeded the PEL for several independent and well-established reasons. RoseyFields’ evaluations examine each of them.

The PELs are outdated and were never health-based to begin with. The overwhelming majority of OSHA’s PELs were adopted in a single action shortly after the Occupational Safety and Health Act of 1970 took effect, when Section 6(a) authorized OSHA to import existing consensus values wholesale as enforceable limits. Most have never been updated since. This is not a contested characterization — OSHA states it on its own website:

“OSHA recognizes that many of its permissible exposure limits (PELs) are outdated and inadequate for ensuring protection of worker health. Most of OSHA’s PELs were issued shortly after adoption of the Occupational Safety and Health (OSH) Act in 1970, and have not been updated since that time.”

OSHA adds that “in many instances these adopted limits are not sufficiently protective of worker health,” and its Hazard Communication Standard requires safety data sheets to list not only the PEL but also the ACGIH TLV and any other limit the employer uses — because the PEL alone is understood to be insufficient. A 1989 effort to modernize hundreds of PELs was vacated on judicial review, and the tables have remained frozen for more than half a century while the underlying science advanced.

The acceptable-risk level built into the PELs is extraordinarily high. As former OSHA Director of Health Standards Adam Finkel, Sc.D., CIH, testified before Congress in 2019, OSHA has interpreted the Supreme Court’s 1980 benzene decision to permit it to stop reducing exposures once the residual lifetime risk of grave disease reaches roughly one in one thousand — whereas environmental statutes direct EPA toward a target closer to one in one million where feasible. An exposure held exactly at a PEL can therefore embody a lifetime risk of serious disease on the order of one in a thousand. Compliance is not safety; it is a risk-management compromise that tolerates a substantial disease rate.

For carcinogens, there is no safe level at all. Under its current carcinogen policy (Current Intelligence Bulletin 68), NIOSH recognizes that there is no safe level of exposure to a carcinogen. It no longer issues a conventional exposure limit for carcinogens and instead publishes only a “Risk Management Limit for Carcinogens” as a starting point for control. For a carcinogenic agent, an exposure below any numerical limit — including the PEL — still carries risk. The disease this produces (cancer, in particular) appears years or decades later, long after the “compliant” exposure occurred.

PELs ignore susceptibility, mixtures, and cumulative dose. A PEL is a single number applied to an average, healthy adult worker over a standard shift. It does not account for individually susceptible workers, for co-exposures that act together, for dermal or take-home exposure, or for the cumulative dose accrued over a long career. A series of individual measurements each below the PEL can still sum to a cumulative dose that the health-effects literature associates with disease.

Sometimes there is no PEL at all. For a number of important agents OSHA has never set a PEL. Where an agent has no PEL, the absence of an exceedance is not evidence of safety — it is evidence that OSHA never set a number to exceed.

2. The Benchmarks RoseyFields Evaluates Exposures Against

Because compliance with a PEL does not establish safety, a defensible industrial hygiene evaluation compares exposures against the more current, health-based reference values. Dr. Rosenfeld’s analyses draw on the full hierarchy, and the divergence among these benchmarks is itself a central finding.

NIOSH Recommended Exposure Limits (RELs) are set by the research agency Congress specifically charged with identifying levels “at which no employee will suffer impaired health.” RELs are frequently more protective than the corresponding PEL and reflect more recent science. For carcinogens, NIOSH’s Risk Management Limit is explicitly a control starting point, not a safe threshold.

ACGIH Threshold Limit Values (TLVs) are consensus guidelines revised far more frequently than PELs and typically substantially lower. ACGIH is explicit that a TLV is a risk-management value, not a license to expose workers up to that value.

Cal/OSHA PELs and other state and international limits are, for many agents, lower and more current than the federal PEL — direct evidence that more protective enforceable limits are both feasible and already in force elsewhere.

EPA health-based reference values (IRIS reference concentrations and inhalation unit risks) are calibrated to general-population risk targets far lower than OSHA’s, and are used to frame occupational exposures in health-based rather than compliance-based terms.

Action Levels — commonly one-half of the applicable limit — exist precisely because a single measurement below a limit does not establish that a worker’s true long-term average was below it. Because daily exposures vary, sound practice seeks reasonable statistical confidence that the true average does not exceed the limit.

When these benchmarks are laid side by side, the recurring finding is stark: an exposure can comply with the PEL while simultaneously exceeding the NIOSH REL, the ACGIH TLV, the Cal/OSHA limit, and the EPA-derived value. That exposure is “in compliance” and unprotected by every current health-based standard at once — which is precisely how a worker gets sick at a level below the PEL.

3. How RoseyFields Evaluates and Reconstructs the Data

Occupational exposure records are frequently sparse, intermittent, and collected for compliance rather than to characterize a worker’s cumulative dose. RoseyFields’ evaluation begins by establishing what the available data can — and cannot — support.

Dr. Rosenfeld evaluates employer industrial hygiene monitoring against the conditions under which it was collected: how many samples exist, over what years, at which tasks and locations, using which analytical method, and whether the sampled conditions represent the worker’s actual job. A handful of area or task samples from a few years cannot characterize decades of exposure, and monitoring gaps are treated as gaps in the record, not as evidence of low exposure. The analytical method matters as much as the sample count: for agents difficult to measure directly, industrial hygiene relies on validated surrogates and standardized methods, and the suitability and limits of each surrogate are evaluated explicitly.

Where direct measurements for the relevant period do not exist, exposure is reconstructed from primary evidence — job and task descriptions, work practices, ventilation and engineering-control conditions, process and equipment data, materials handled, and the peer-reviewed industrial hygiene literature reporting measured concentrations for comparable tasks. Reconstructed exposures are expressed both as concentration and as cumulative dose (concentration integrated over duration), so they can be compared to the health-based benchmarks and to the exposure ranges the health-effects literature associates with disease. This is the step that most directly demonstrates sub-PEL harm: a reconstructed cumulative dose can fall below the PEL at every point and still land squarely within the range at which the epidemiologic and toxicologic literature reports elevated disease risk.

The evaluation is framed throughout by the hierarchy of controls. The recognized order of protection is elimination or substitution of the hazard, then engineering controls, then administrative controls, and only last personal protective equipment. An exposure “kept below the PEL” through the least effective measures — while feasible engineering controls went unimplemented — is evaluated accordingly. The analysis also accounts for the OSHA General Duty Clause, Section 5(a)(1), which independently requires employers to furnish a workplace “free from recognized hazards that are causing or are likely to cause death or serious physical harm.” That obligation is not discharged by mere compliance with a specific PEL.

Application

This framework applies wherever a party asserts that compliance with an exposure limit establishes that a worker was safe. Typical questions RoseyFields addresses include: whether an employer’s monitoring program was adequate to characterize the exposures it measured; whether a worker’s cumulative dose over a career exceeded current health-based benchmarks even where individual measurements complied with the PEL; what that cumulative dose was when direct records are incomplete; whether the exposure fell within ranges the health-effects literature associates with disease; and whether feasible controls higher in the hierarchy would have reduced it.

Methodologies applied in this practice are evaluated under Daubert and analogous standards. The conclusions rest on the recognized science of industrial hygiene and on the published positions of the responsible agencies themselves — including OSHA’s own acknowledgment that its PELs are outdated and, in many instances, not sufficiently protective of worker health.

For completeness, the countervailing point should be stated plainly: the PEL’s one advantage over the REL and TLV is that it is legally enforceable, and an employer meeting every applicable PEL has satisfied the specific numerical requirements OSHA can cite it under. That is a statement about legal compliance, not about health — and preserving that distinction is the entire purpose of this analysis.

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