COMAH Application at surface treatment sites

OC 655/7 - Version 2

Author Unit/Section: HID CI4A

Target Audience: FOD Inspectors, HID Inspectors


To advise FOD and HID staff on the current position regarding the classification of surface treatment baths containing chromic acid, the consequent effect on application of the Control of Major Accident Hazard Regulations (COMAH) and the interim policy on regulation of surface treatment companies. FOD/HID demarcation arrangements are described in paragraphs 15-17 but for most sites, FOD will continue to be the enforcing Directorate.


1Chromium trioxide (CrO3) was reclassified in the CHIP Approved Supply List (ASL). 8th edition, from toxic (T) to very toxic (T+). These changes were implemented under CHIP 3.1 amendments on 31 October 2005. Application of COMAH is based on the CHIP classification system.

2  CrO3 is supplied as crystal or flake. When dissolved in water it forms a chromic/dichromic acid solution, which is used at a variety of concentrations for, chrome plating, passivation, anodising, etching of plastics prior to plating and electro polishing. The terms 'chromium trioxide' and 'chromic acid' have been used synonymously in the surface engineering industry. For example, drums of chromium trioxide are often labelled by the manufacturer as chromium trioxide (chromic acid). This has led to confusion over whether chromic acid should have the same T+ classification as chromium trioxide. Furthermore, there is evidence that chromic acid should have a T+ classification and its classification may be reviewed in due course as part of the European reclassification process.

3  There has been considerable discussion (including EC level) over the correct classification of baths containing chromic acid and consequent Seveso application.  This has to be resolved at a European level and is still under discussion.  However, pending an agreed outcome the following line, which has been agreed with Policy, Legal Advisors and the Environment Agency/SEPA should be taken.

Current classification of chromic acid solution

4  Chromium trioxide, dissolved in a plating bath solution, should be considered to be chromic acid (H2CrO4), CAS 7738-94-5, EINECS# 231-801-5.

5  Chromic acid is:

  • a substance, rather than a preparation containing chromium trioxide
  • a chromium VI compound that has a classification prescribed by the CHIP ASL under the group entry 'Chrome VI compounds, with the exception of barium chromate and other compounds specified elsewhere in the ASL'.
  • currently classified as

    Carcinogenic Cat 2, R49 'may cause cancer by inhalation'; R43 'may cause sensitisation by skin contact' (these classifications are not relevant to COMAH).

    Dangerous for the environment R50/53 'very toxic to aquatic organisms' (this classification is relevant for COMAH application).

COMAH impact

6  Quantities of chromium trioxide crystal or flake (ie raw material) will count towards T+ qualifying thresholds (5 tonnes for Lower Tier and 20 tonnes for Top Tier) and/or R50/53 thresholds (qualifying quantities for R50/53 are 100 tonnes for LT and 200 tonnes for TT). Where COMAH threshold quantities are exceeded normal duties and procedures apply.

7  Quantities of chromic acid held in plating baths should, in the interim, count towards COMAH qualifying thresholds for the generic category of substances dangerous for the environment (R50/53) and not towards the T+ (R26) thresholds.

COMAH duties - notifications, MAPPS and safety reports

8  COMAH notifications received to date as a result of the reclassification should be reviewed with the Operators in the light of paragraphs 6 and 7 above to establish whether COMAH applies. HID CI teams should retain all notifications and send a copy to CI4 (Gerry Adderley) for those sites where COMAH applies. 

9  In addition to notification, operators at surface treatment sites holding dangerous substances above the COMAH qualifying quantities should prepare a Major Accident Prevention Policy (MAPP) and keep it available on site (COMAH Lower Tier duty), submit a safety report (including a MAPP) and prepare an on-site emergency plan.  Full details of all the COMAH duties and further guidance is available in the Guide to COMAH (L111)

10  Where the contents of the plating bath(s) containing chromic acid would trigger COMAH LT or TT thresholds if the solution were to be reclassified as T+, we currently do not require operators to submit notifications (COMAH Regulation 6). However, operators should be encouraged to provide basic details including name, address, contact name and information on dangerous substances kept on site including their chromic acid baths. HID CI teams should keep a list of those sites together with those that have notified. This will enable us to maintain contact and ensure that they are made aware of further developments. Work with these sites is non-chargeable.

11  Such sites are not required to prepare a Safety Report or MAPP, however they should have preventive measures in place under HSWA and have (or be encouraged to put in place) arrangements to ensure they are adequately prepared to deal with any potential major accidents including loss of containment from surface treatment baths.

Major accident scenarios where COMAH applies

12  Major accident scenarios arising from the use of CrO3 are likely to be environmental. Work carried out by HSL indicates that fire involving entrainment of CrO3 in the smoke plume is unlikely to present a major accident hazard off-site in quantities less than 50 tonnes.

13  Where cyanides are also held the range of major accident scenarios includes those which may cause harm to people for example, inadvertent mixing of incompatible chemicals through mischarging or spillage.

14  Further guidance on major accident scenarios and associated risk reduction measures may be found in COMAH Guidance for the Surface Engineering Sector . This is particularly useful for LT sites preparing MAPPs. Additional guidance on risk assessment is also included - which is useful for TT sites preparing safety reports.


15  The overall effect of this policy line is that only a small number of surface treatment establishments are likely to be brought within COMAH. FOD should continue to be the enforcing Directorate for the remainder and the continuing uncertainty over classification should not be taken as reason for delaying or avoiding any planned interventions at such sites. Where there are any doubts as to the application of COMAH eg concerning the CHIP classification rules for substances in solution or the aggregation rules for generic hazard categories, then FOD inspectors should speak to the local CI Inspection team for further advice and clarification.

16  The small number of sites brought into COMAH should be regulated by the Competent Authority (ie HID and EA/SEPA).  However, where it is practicable and proportionate to do so, HID will establish a COMAH topic enclave with the remainder of the establishment retained by FOD in line with OC 18/11.

17  The detail of any COMAH topic enclave, or whether HID should regulate the non-COMAH parts of a site should, as at present, be subject to local discussion between HID/FOD involving the EA/SEPA where appropriate. For example, it may be more efficient and effective for HID to regulate the whole site where the non-COMAH activities are relatively small scale or directly ancillary to the surface treatment work.  Alternatively, where the major accident scenarios are solely environmental then HID's involvement may be restricted and FOD should lead on non-major hazard intervention across the site.

Health issues – FIT 3

18  Conventional health issues often predominate at surface treatment sites and may present significant risks to the workforce (cancer, asthma and allergic contact dermatitis).  Many electroplating sites have a history of poor maintenance of COSHH control measures. Inspectors with responsibility for surface treatment sites should familiarise themselves with current guidance and intervention initiatives particularly SIM 03/2005/16 'Reducing the risk of ill-health from hexavalent chromium compounds in the electroplating industry' and the four associated guidance documents agreed with the Surface Engineering Association.

19  Inspectors are not being asked to carryout special visits to support this central intervention initiative, as time has not been allocated in the work plan. However, it is essential that Inspectors visiting facilities using hexavalent chromium are aware of the new guidance that has been issued which is aimed at achieving compliance with COSHH. Inspectors should ensure that these standards are being met where opportunities arise during other interventions. For staff in HID, this is not COMAH work and is therefore non-chargeable. CI staff should record the work on COIN against the Carcinogens work stream.

Further information

Manufacturing Sector.

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Updated 2022-08-16