Occupational Hygiene Monitoring Plan (OHMP)
A Systematic Framework for Identifying, Assessing, and Controlling Workplace Health Hazards
An Occupational Hygiene Monitoring Plan is the foundational document that governs how a business identifies, measures, evaluates, and controls worker exposure to health hazards in the workplace. It is not a one-off report or a box-ticking exercise. An OHMP is a living, structured programme that translates the general duty of care under the Work Health and Safety Act 2011 into a practical, auditable system of exposure management. For any business where workers are exposed to airborne contaminants, noise, vibration, thermal stress, biological agents, or radiation, the OHMP is the document that ties together every other compliance activity — from baseline air monitoring to health surveillance, from engineering control verification to respiratory protective equipment programmes.
The Legal Duties an OHMP Helps You Meet
Neither the WHS Act nor the NSW WHS Regulation 2025 requires a document called an occupational hygiene monitoring plan, and neither prescribes a format for one. What they do impose are monitoring duties that are explicit and enforceable. Section 19(3)(g) of the WHS Act requires a person conducting a business or undertaking (PCBU) to ensure, so far as is reasonably practicable, that the health of workers and the conditions at the workplace are monitored for the purpose of preventing illness or injury. In NSW, section 50 of the Work Health and Safety Regulation 2025 requires a PCBU to ensure that air monitoring is carried out to determine the airborne concentration of a substance or mixture to which an exposure standard applies if the PCBU is not certain on reasonable grounds whether the concentration exceeds the exposure standard, or if monitoring is necessary to determine whether there is a risk to health. The results must be recorded and kept for 30 years, and must be readily accessible to people at the workplace who may be exposed. Section 50 does not say who must carry out the monitoring or which methods must be used, but monitoring that cannot show whether the exposure standard is exceeded does not answer the question the section asks. In practice, a qualified occupational hygienist sets the monitoring strategy: who is sampled, for which contaminants, by which method and how often. That strategy, written down, is the OHMP.
Core Components of an OHMP
Workplace Characterisation & Process Mapping
Thorough mapping of every process, task, and operation that generates a health hazard. Documents substances used or generated, physical state, duration and frequency of worker exposure, existing controls, and ventilation conditions. Determines the scope of the entire monitoring programme.
Similar Exposure Group (SEG) Identification
Groups workers with similar exposure profiles based on task, substance, duration, physical environment, engineering controls, and PPE use. SEG composition directly determines the number of monitoring samples required and the statistical validity of the exposure assessment.
Contaminant Identification & Prioritisation
Identifies every substance of concern and prioritises based on toxicity, severity of health effects, likelihood of exposure at levels approaching the WEL, and number of workers exposed. Accounts for mixed-exposure scenarios using the additive formula.
Monitoring Strategy & Sampling Design
Specifies monitoring type (personal, static, biological), sampling equipment and analytical methods, sampling duration, number of samples per SEG, and frequency of monitoring rounds. Defines the statistical approach to data analysis.
Trigger Levels & Action Criteria
Defines tiered action thresholds: below 10% WEL (reduced monitoring), 10-50% WEL (routine monitoring), above 50% WEL (enhanced monitoring and control review), approaching/exceeding WEL (immediate corrective action and health surveillance referral).
Health Surveillance Integration
Links monitoring data to health surveillance protocols. Specifies which surveillance is triggered by monitoring results, how data flows to the health surveillance provider, and how surveillance findings feed back into the monitoring strategy.
Documentation & 30-Year Record Retention
Air monitoring results recorded and kept for 30 years after the record is made, as section 50(2) of the NSW WHS Regulation 2025 requires, and kept readily accessible to people at the workplace who may be exposed (section 50(3)). Specifies how sampling records, calibration certificates, laboratory reports and interpretive reports are filed with those results, the documentation standards and format, and the process for making results available to workers.
OHMP and the December 2026 WEL Transition
The transition to Workplace Exposure Limits on 1 December 2026 represents the most significant change to Australian occupational exposure standards in decades. For businesses that already have an OHMP, the transition requires a formal review to update all referenced exposure limits, recalculate trigger levels against the new WEL values, reassess SEGs where tightened limits change the risk profile, and identify processes where existing controls may be insufficient. For businesses without an OHMP, the transition period is the strongest argument for developing one. Baseline monitoring before December 2026 provides the data needed to understand current exposure levels, identify gaps, and plan control upgrades.
Get Started with an OHMP
If your workplace involves airborne contaminants, noise, chemical handling, or any other health hazard, the WHS duties to manage those risks, including air monitoring where section 50 of the WHS Regulation applies, exist whether or not you have a written plan. An OHMP is a practical way to show you are meeting them, and the December 2026 WEL transition makes this the right time to act.