International Qualifications M-Series FAQs

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BOHS would always recommend professionals to see their national professional body and awarding scheme as the best place to seek qualifications from. We are committed to the International Labour Organisation’s Conventions on Occupational Health (161 and 155) which promote strong, independent national professional bodies. The context of occupational hygiene practice varies from country to country and national bodies are best to set standards. Income from qualifications also provides the basis of financial security for national professional bodies and a means of control of their own standards.

A number of for-profit and not-for-profit bodies offer international training and certifications. While the IOHA NAR scheme recognises only end point qualifications, we would recommend that only bodies who are listed on the National Accreditation Recognition (NAR) Committee – IOHA are independently verified as having processes and infrastructure which can assure high quality occupational hygiene training and awards at the professional level of practice.

We would therefore only recommend that a candidate uses a UK qualification when:

  • Where the candidate intends to work in the UK, for an organisation tied to UK/European standards or in a country where UK qualifications are recognised as being preferred; or
  • Where the subject matter cannot be examined locally or to the level of expertise required by the candidate; and/or
  • Where there is a need for an assessment of professional skills by a qualified professional that is independently examined to an internationally accepted standard of practice.

At present, only BOHS delivers qualifications internationally that meet criteria 1 and 3.

OHTA is a charity set up to distribute and update free occupational hygiene training materials. OHTA is not a recognised awarding body in the UK (or internationally) and so made arrangements with BOHS for us to certify that candidates have met BOHS’s qualifications standards for W201, W500 and ICertOH. We do not award OHTA qualifications any more, but continue to award the end-point qualification, ICertOH. W500 awards and W201 awards continue as before, renamed M500 and M200 awards respectively. W500 awards continue to be valid for ICertOH completion and national recognition purposes.

We understand that OHTA continues to provide manuals and certification through MCQ tests, but no longer provides professional assessments. OHTA courses now no longer have recognised awards, other than when awards are made through AIHA and SAIOH in relation to OHTA201.

BOHS M500 examinations test skills, knowledge and competency in exactly the same way as W500. Study materials are available freely to download and courses can be booked online via Course Search ( Having been largely unchanged while under the management of OHTA, BOHS has corrected a number of minor technical errors prior to republication and is currently in the process of undertaking revisions of  the substantive content to bring them up to date with current international standards.

OHTA500 assessments now no longer examine the range of intellectual and practical skills tested by the W500 series. OHTA500 courses may be valuable for revision preparation for recognised professional qualifications, including for the M500 exam series or to meet coursework requirements for other awarding bodies, but are not recognised in the UK as qualifications, so will not prepare you to meet ICertOH standards, for which BOHS acts as the independent examining body.

BOHS is the only recognised awarding body for Occupational Hygiene qualifications based in the UK. It is the regulatory body for overseas qualifications under the Regulated Professions Act 2022 and runs the UK’s statutory register for Occupational Hygiene Professions Register of Occupational Hygiene Professionals - British Occupational Hygiene Society (BOHS). In order to meet the qualifications requirements to work in the UK and for many UK companies, you will need a BOHS awarded qualification. BOHS has relationships with a number of examination centres internationally. There are hundreds of courses and exam opportunities each year face to face and online (where there is no need for a practical element). You can find a list here Course Search (

There is high demand for occupational hygienists in the UK and at the moment, there is no other recognised awarding body which currently meets UK standards, as set out in the BOHS Statement of Occupational Hygiene Competencies - British Occupational Hygiene Society (BOHS). We are in discussions with other bodies about them working with us. Please note that as of 1st January 2024, courses provided by training intermediaries, such as the Occupational Hygiene Training Association will only be accepted as meeting UK professional standards, if examined by BOHS (i.e. you register and pass an M500 exam).

Previous awards of BOHS, such as our W500 awards, will continue to be recognised. You can even sit new M500 courses if you have done other training because the examinations are no longer tied to particular organisations. However, to ensure that you are properly prepared for M500 examinations, please refer to the open access materials which are free to access and have been updated Qualifications - British Occupational Hygiene Society (BOHS). These materials should be used, rather than other material distributed on the internet, which have not been quality assured by BOHS and which may require you to give your personal data or ask you for payment.

BOHS examinations meet the criteria set out for coursework for BGC CIH Candidate Handbook ( (note page 7), in relation to professional examinations. BOHS is a member of the IOHA NAR scheme, as well as IOHA. The European Platform on Occupational Hygiene is shortly to announce a competency framework for Europe and our qualifications will remain aligned to this. Our competency framework is also aligned to the European framework for higher education and matches the European Credit Transfer system. As BOHS awards under its Royal Charter (the same as Oxford and Cambridge Universities), it enjoys national and international recognition as the UK’s exclusive awarding body.


Please refer to this document for a more comprehensive look at the differences between the BOHS and OHTA qualifications.

While BOHS provides a European-style qualifications route, a major professional qualifications route is through certification as an Industrial Hygienist. CIHs will be recognised for practice in the UK, subject to finalisation of a bilateral agreement and those studying for BGC examinations, such as through AIHA’s courses or those undertaking OHTA500 courses can seek professional recognition once they have completed their CIH examinations.

In the alternative, candidates may sit M500 examinations, which are a continuation of the W500 series to progress to CertOH or ICertOH for professional recognition.