Explainer: What occupational hygienists do at work

Occupational hygienists help businesses identify and control health hazards that can cause illness long after a worker's shift has ended. 

Hidden hazards

Workplace safety is often associated with hazards that can cause immediate injury. Occupational hygiene deals largely with a different problem: exposures whose effects may be difficult to see and may emerge only after repeated contact over months or years. 

Dust, fumes, vapours, gases, chemicals, noise, vibration, radiation and extreme temperatures can all fall within an occupational hygienist's work. The discipline combines elements of science and engineering to identify hazards, assess workers' exposure and determine how those exposures can be controlled. 

That role matters in New Zealand because work-related disease accounts for a substantial share of serious occupational harm. WorkSafe estimates that work-related ill-health causes about 750 to 900 deaths and 5,000 to 6,000 hospitalisations each year. Its research has also found that cancer and respiratory disease account for about 70% of estimated work-related deaths. 

The risks are not confined to heavy industry. Occupational hygienists work across manufacturing, mining, construction, hospitals, public utilities and other workplaces. The term "industrial hygiene" remains common in the United States, but occupational hygiene has become the broader description because exposure risks can arise wherever people work. 

WorkSafe put the profession under a fresh spotlight in July 2026 when it released practical material on workplace exposure standards, including a guide for businesses considering whether to engage an occupational hygienist. The regulator said businesses had reported difficulty understanding and applying exposure standards, along with concerns about monitoring costs and access to specialists. 

Old discipline

The principle behind occupational hygiene predates modern health and safety regulation by centuries.

In Britain, one early milestone came in 1726, when Thomas Benson obtained a patent for using wet grinding to control flint dust in pottery production. By 1864, British factory legislation was requiring ventilation to reduce harmful gases and dust, although the science needed to determine acceptable exposure levels was still undeveloped. 

During the following decades, workplace health increasingly became a field of measurement as well as observation. British Factory Inspector Thomas Legge proposed an occupational exposure limit for lead in 1912. Research into coal workers' pneumoconiosis followed, while the middle of the 20th century brought more formal definitions of respirable dust and broader lists of exposure limits. 

Those developments helped establish a core method that remains recognisable today: anticipate hazards, recognise them, evaluate exposure and control the risk. The International Occupational Hygiene Association defines the discipline around those four functions, with the objective of protecting worker health and the wider community. 

Modern occupational hygiene therefore involves more than taking samples. Measurement is one tool within a process that begins with understanding the work itself.

A hygienist may examine how a substance is used, how often a task occurs, how many workers are involved and what controls are already in place. They may then decide that monitoring is needed, select an appropriate sampling strategy and interpret the results in the context of the work. 

Measuring exposure

Exposure monitoring is useful when a business does not know how much of a workplace hazard its employees encounter, or when it needs to check whether existing controls are doing their job.

Personal air sampling, for example, can estimate the concentration of an airborne contaminant that a worker breathes during a task or shift. Other assessments may examine noise, vibration or contamination on surfaces. Biological exposure monitoring can involve testing blood or urine for a substance or one of its metabolites, although this raises additional consent and privacy requirements. 

The resulting number is not useful in isolation. It needs context.

New Zealand's workplace exposure standards provide guidance values for airborne contaminants. WorkSafe says the standards and biological exposure indices are risk criteria rather than prescribed exposure standards or automatic regulatory limits. They should be interpreted by people with suitable training and experience. The regulator advises against untrained users treating them as a simple compliance test. 

The 16th edition of WorkSafe's workplace exposure standards and biological exposure indices took effect in July 2026. 

The distinction is important. A measurement below a guidance value does not remove the need to manage a known hazard. Likewise, monitoring does not control exposure by itself. WorkSafe describes workplace monitoring as a means of assessing risk and checking controls, rather than a substitute for reducing the hazard. 

That is why an occupational hygiene assessment may produce recommendations that have little to do with buying more monitoring equipment. The response might instead involve altering a process, improving extraction, substituting a material, enclosing a source or changing how work is organised. Personal protective equipment generally sits behind controls that reduce exposure at its source. 

Choosing expertise

The title "occupational hygienist" alone does not tell an employer whether a consultant has the right expertise for a particular job.

WorkSafe recommends checking qualifications, experience and the scope of a hygienist's competence. Relevant qualifications can include science degrees, postgraduate occupational hygiene study and recognised specialist training. International professional certification provides a further measure of competence based on education, experience and examination. 

New Zealand does not currently have its own certification programme accredited under the International Occupational Hygiene Association's national recognition system. Practitioners may instead hold recognised overseas credentials. 

Businesses can also use professional registers to narrow their search. WorkSafe points employers towards the New Zealand Occupational Hygiene Society and the Health and Safety Association of New Zealand. For occupational hygienists, eligibility for the HASANZ Register is tied to Full Membership of the New Zealand Occupational Hygiene Society, with applicants' credentials checked against the society's membership records. Consultants must also provide evidence of relevant insurance. 

Registration is only part of the selection process. A hygienist experienced in asbestos work may not necessarily be the best person for a complex noise assessment or a chemical exposure investigation. WorkSafe advises businesses to ask about recent comparable work, relevant experience and the methods proposed for the assessment. 

That need for specialist judgement is one reason workforce capacity has become an issue. HASANZ and the occupational hygiene profession have been working to increase the number of qualified practitioners in New Zealand. The initiative has identified limited postgraduate study opportunities and a need to make more science graduates aware of occupational hygiene as a career. 

WorkSafe also began supporting an occupational hygiene workforce development project in 2018, including scholarships and mentoring. 

Site assessment

Hiring an occupational hygienist should begin with a defined problem rather than a request to "do some testing".

WorkSafe suggests giving a prospective consultant information covering what the hazard is, why help is required, where the work happens, who may be exposed and when the exposure occurs. Existing procedures, safety data sheets and previous monitoring results can also shape the assessment. 

A proposal should explain what will be assessed and how. It should identify the people carrying out the work, their qualifications, the sampling or assessment methods to be used, the expected timetable and the cost. A competent hygienist should retain responsibility for the assessment when junior staff are involved. 

The site visit itself is partly scientific and partly observational.

A hygienist may walk through the workplace while normal operations are running, speak with workers and supervisors, examine procedures and records, inspect extraction systems or protective equipment, and carry out measurements. WorkSafe specifically advises businesses not to tidy up or change normal processes for the visit because the specialist needs to see the conditions workers usually experience. 

Worker input can be especially useful. Employees may know that a dusty task happens only at the end of a production run, that extraction performs differently on certain equipment or that a strong smell appears during a process change. An assessment that captures only an unrepresentative period can miss variations that influence exposure. WorkSafe's guidance therefore asks businesses to identify relevant shifts, seasons, operating conditions and affected roles before the work begins. 

Practical action

The final product of an occupational hygiene assessment is not the monitoring result. It is a decision about risk.

A useful report should explain what was assessed, the methods used, the results, what those results mean and what should happen next. Supporting laboratory data and equipment calibration records may sit behind the main findings, but the recommendations should be understandable to managers and workers who are not occupational hygiene specialists. 

WorkSafe recommends prioritising actions according to risk. The most serious exposures should be addressed first. Businesses should also understand how each recommendation relates to the evidence collected rather than treating the consultant's report as a document to file away. 

That reflects the central purpose of occupational hygiene. The profession uses measurement, toxicology, engineering and observation, but its objective is prevention. Its value lies in identifying where harmful exposure occurs and determining how work can be changed before repeated exposure becomes occupational disease. 

For employers, the practical question is therefore not whether every workplace needs regular specialist testing. It is whether the business understands its health hazards well enough to know what workers are exposed to and whether its controls are effective. Where those answers remain uncertain, occupational hygiene provides a structured way to find them.