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Industrial timber treatment plants

These web pages provide guidance for timber treatment plant operators on how to comply with legal requirements for the industrial treatment of timber.

Timber treatment plants are used for impregnating timber with various types of preservatives and/or fire retardants. As the timber is placed in a vessel and impregnated by a preservative under pressure the vessel is classified as an autoclave.  

There have been three fatalities in the UK since 2008 involving autoclaves and the HSE have produced guidance on Safety requirements for autoclaves. This provides information on the safe operation and maintenance of these devices. It specifically addresses the risks associated with safeguarding, training and maintenance.

The safe operation of timber treatment plants depends on having correct design and construction, suitable maintenance procedures, and correctly trained and competent operators. This will ensure that the risks from exposure to the treatment chemicals has been adequately controlled and that the plant is run safely.

Timber treatment  vesselTimber treatment vessel

The Wood Protection Association (WPA), the technical and advisory body for the timber treatment industry, has produced a Timber Treatment Installations Code of Practice for Safe Design and Operation (COP). This has been endorsed by several regulatory authorities including the HSE and Environment Agency. If you adopt the principles set out in the Timber Treatment Installations Code of Practice for Safe Design and Operation (COP) then you should be doing enough to comply with the law.

Some of the information contained in the COP has been reproduced here with the permission of the WPA, but operators will benefit from reading the full document. This can be purchased from the WPA - contact e-mail:

Key relevant health and safety law

1. Industrial treatment of timber involving wood preservatives attracts the Control of Pesticides Regulations (COPR) and the Biocidal Products Regulations (BPR). You should only use products approved under these Regulations. For further information see Biocides.

2. Employers should do everything reasonably practicable to ensure their activities are safe and without risks to health. This includes providing and maintaining safe equipment and systems of work, suitable training, instruction, supervision and staff welfare facilities. See HSE’s website ‘Health and safety made simple’ for further information.

It is important that employers provide appropriate personal protective equipment, as detailed in the information from the wood preservative supplier i.e. product labels and safety data sheets. It is also important that that good personal hygiene practices are followed. You should have washing and changing facilities within (or very close to) the treatment plant area. These should be designed to prevent the spread of contamination from work wear to personal clothing.

You should also:

3. HSE’s COSHH website gives you information on what the law requires and advice on completing COSHH assessments. Your product safety data sheets will help you assess all work activities that may expose employees to any hazardous substances (this is your ‘COSHH assessment’). They will also help you decide if The Pressure Systems Safety Regulations 2000 (PSSR) apply to your treatment plant i.e. if the treatment fluid is a ‘relevant fluid’ (see below).  To prevent or adequately control exposure of substances hazardous to health (COSHH) there should be total containment for the:

In addition to their primary containment, these should all be located within secondary containment, generally provided by impervious bunding. Bunding should:

See Timber Treatment Installations Code of Practice for Safe Design and Operation for more information on containment.

Examples of engineering and operational measures used in treatment plants that will control exposure to hazardous substances include:

Where there is significant exposure to wood preservatives, you are required to have health surveillance for the early detection of any health problems. This should be under the control of a qualified occupational health professional. For further information on health surveillance see  Managing construction health risks: Health surveillance

Health surveillance is not a substitute for preventing or adequately controlling exposure in the first place but it will help you evaluate how effective your control measures are.

You should keep records that include:

Health surveillance is only of value if you act on the results. Where it shows that a worker’s health is being affected by their work you should:

4. Treatment vessels should have a thorough examination by being examined by a competent person periodically if they contain a ‘relevant fluid’ (as defined under PSSR) and be under a Written Scheme of Examination.  However, all treatment vessels, whether PSSR applies or not, should have suitable and effective arrangements to make sure that they are properly maintained. Where appropriate, this should take into account advice from the manufacturer/supplier on appropriate methods of testing, particularly where internal examination is difficult. For more information on through examination and maintenance and inspection requirements, see Safety requirements for autoclaves and work equipment

5. The Pressure Systems Safety Regulations 2000 (PSSR) apply to treatment plants when:

When PSSR applies, the following information should be marked clearly on the vessel:

Vessels should be fitted with a safety relief valve set to the design pressure of the vessel as well as a second relief valve to control the working process pressure, preferably set at 10% below the design pressure. Both valve discharges should be directed to a tank.

Make sure that the timber treatment vessel door is always properly closed and locked otherwise it can blow open during the process by either internal pressure or the weight of the fluid. Doors can also be opened at the wrong time. To prevent these dangers options include fitting controls that:

See Safety requirements for autoclaves for additional information on safety measures.

For more information see HSE’s Pressure Systems website and the Safety of Pressure Systems (ACOP) - L122

Updated 2014-12-10