Chemical Exposure Monitoring (CEM) in Malaysia: When, How Often, Who

What is chemical exposure monitoring (CEM)?

Chemical exposure monitoring measures how much of a chemical hazardous to health is in the air exposed workers breathe, and compares it with the permissible exposure limits in Schedule I of USECHH 2000. It shows whether your controls keep exposure below those limits. It is also called air monitoring or industrial hygiene monitoring.

DOSH sets the method in its Guidelines on Monitoring of Airborne Chemical Hazardous to Health 2022. CEM measures; it does not decide the controls. That is the job of the CHRA, explained in our CHRA guide.

When does the law require chemical exposure monitoring?

When your CHRA says it is needed. Regulation 26(1) of USECHH 2000 requires monitoring where the assessment shows it is required, or needed to keep exposure adequately controlled. DOSH’s 2025 hygiene technician FAQ adds that once the CHRA assessor recommends CEM, the employer must carry it out.

• Every CHRA must state whether exposure monitoring is necessary, work unit by work unit (regulation 9(2)(h)).
• Schedule II chemicals, such as lead, benzene, isocyanates or free crystalline silica, need repeat monitoring (regulation 26(2)).
• Contractors doing work for you on your premises are covered too (regulation 4(1)(a)).

How often must chemical exposure monitoring be repeated?

It depends on the chemical and the last result. Schedule II chemicals: not more than six months, until the assessor is satisfied monitoring is no longer needed (regulation 26(2)). Other chemicals: the DOSH 2022 Guidelines set six months for results at or above the limit, and 12 months from half the 8-hour limit.

How is chemical exposure monitoring carried out?

In nine steps set by the DOSH 2022 Guidelines, running from a preliminary survey and grouping workers into similar exposure groups to sampling, a compliance test and the report. Samples are taken in each worker’s breathing zone, because the limits refer to personal exposure; area samples only help find sources (Guidelines 1.6.1).

• Three samples minimum per chemical in each exposure group; groups of fewer than three workers are sampled again on another day or shift (2.5).
• Six more if any of the first three falls between 10% of the limit and the limit, then a statistical compliance test on all nine (2.5, 6.3).
• Duration to match the limit: full shift for the 8-hour limit, 15 minutes for STEL and MEL, three or more peak-time samples for a ceiling limit (4.1 to 4.3).
• Calibrated pumps: checked before and after; a flow error above 10% voids the sample (3.6).

These rules also set your quote: the number of chemicals, exposure groups, close results, shift length and short-term limits decide the field and laboratory work, and a registered hygiene technician cannot drop them to cut the price.

What must a chemical exposure monitoring report contain?

A report in the DOSH format, delivered within one month and presented to you or your safety and health committee. It names the hygiene technician and registration number, explains how workers and sampling times were chosen, compares each result with the limit and says when to monitor again.

• Method, equipment serial numbers and calibration dates, and the reasons for the number and duration of samples.
• Results per chemical and work area against the limit, with the statistics where nine samples were taken.
• Appendices: certificate of competency, the signed notification form, calibration certificates, calculation sheets, the laboratory’s certificate of analysis and a layout plan with worker positions (chapter 7).

How do you compare chemical exposure monitoring providers?

Compare the sampling plan, not the total. Ask every provider for the same five things: a registered hygiene technician, an approved method for each chemical, an accredited laboratory, a written sampling strategy and the full DOSH report format. Quotes that differ on these five cannot be compared fairly.

Not in a CEM quote: control works, medical surveillance for Schedule II chemicals through our workplace health service (see our medical surveillance guide), and the ventilation test due at least every 12 months by a hygiene technician registered for that work (HT2, regulation 17).

What does it cost to skip or delay monitoring?

More than the monitoring. USECHH sets no penalty of its own, so section 51 of Act 514 applies: a fine of up to RM100,000, up to one year in prison, or both, plus a fine of up to RM2,000 a day while the offence continues. Directors can be charged with the company (section 52).

OSHMED Solutions Sdn Bhd, based in Kajang, Selangor, serves employers across Malaysia and quotes in writing. OSHMed scopes and coordinates chemical exposure monitoring from your CHRA. It is carried out by a DOSH-registered hygiene technician, as regulation 26(3) requires, and ends with a written report that names the responsible registered person and their myKKP registration number, so you can verify it on the DOSH register. See our assessment services and services.

Before you decide: three common objections

Three objections come up when employers plan chemical exposure monitoring: a round was done last year, the safety officer has a gas detector, and area samples look cheaper. Each is checked below against USECHH 2000 and the DOSH 2022 Guidelines, so the decision rests on the rules.

"We already did monitoring last year."

For a Schedule II chemical, once a year is not enough: the interval is not more than six months (regulation 26(2)). For other chemicals, a result at or above the limit also means six months.

"Our safety officer has a gas detector."

Direct-reading instruments help trace sources, but they can react to other substances and give false readings (Guidelines 3.2). Apart from checks before confined-space entry, a registered hygiene technician must do the monitoring (regulation 26(3)).

"Area samples are cheaper."

The limits refer to personal exposure in the breathing zone, so area samples alone do not show compliance (Guidelines 1.6.1). They help find sources and choose which workers to sample.

Frequently asked questions

Your next step

Find the monitoring recommendation in your CHRA, then fill in the scope builder above or send us your chemicals, work units, headcount and shifts. OSHMed will reply with a written quote.

Noise risks on the same site? We can plan them in the same site visits. See our noise risk assessment guide.

Sources and references

Disclaimer: This article is general information for employers and is not legal advice. Requirements depend on your workplace, processes and the current law. For a decision on your premises, speak to a DOSH-registered competent person or contact DOSH (JKKP).