Health and safety procedures for LOSP and other treated timbers

Health and Safety Procedures for Treated Timbers fig 1

The chemicals used in timber preservatives have varying levels of toxicity, so it is vital to take suitable health and safety precautions when handling and working with any freshly treated timber and when disposing of such waste.

This information was confirmed as current in February 2016. It originally appeared in Codewords newsletters prior to January 2014.

  • Published on 1 May 2007
  • 1st edition

LOSP (light organic solvent-based preservative) treatments were introduced in the 1990s to treat timber in its finished form after machining and drying. Water-based treatments cause finished timbers to swell and distort, whereas LOSP treatments, using an organic solvent base (as the vehicle for treatment chemicals), do not affect dry, finished timber.

The organic solvents in LOSP-treated timber will evaporate after exposure to air (the time it takes to evaporate is temperature- dependent), but some people may experience health problems, such as skin rashes, eye irritations, headaches or light-headedness when working with this timber. These problems are more likely to occur when the timber has not had enough time for the solvents to evaporate or 'flash-off'.

'Flashing off' and storage of LOSP-treated timber

The Timber Preservation Council states that, before dispatch from the treatment site, 'LOSP-treated timber shall be held in fillet (every layer) for a minimum of four days in a well-ventilated area. Alternative methods may be used to reduce residual solvent to equivalent levels'.

This procedure allows solvents time to 'flash off' before the timber leaves the treatment plant. Ideally, it should be stored without protective wrappings in an area with double-ventilated openings or an air extraction system. Other methods may be acceptable to achieve the same level of 'flash-off'.

If timber is delivered before adequate 'flash off' has been achieved, timber treaters should advise recipients, buyers or both of the date of treatment and the time needed for the timber to 'flash-off' before use. The season and weather will affect the required period.

All recipients of LOSP-treated timber, such as merchants and pre-nailers, should allow any residual solvent vapours to dissipate from the timber received by placing it in a well-ventilated, covered space with the protective wrap removed.

Precautions when using LOSP-treated timber

  • Do not use LOSP-treated timber that has not been adequately 'flashed-off'.
  • Avoid working with fresh LOSP-treated timber in an unventilated and confined space.
  • Wear gloves and long sleeves for protection against splinters and cuts during handling.
  • Where there is prolonged contact with timber that has not 'flashed-off' (such as in treatment plants), use an impervious work apron, long sleeves, solvent-resistant gloves, goggles and a filter mask with the proper cartridge.
  • Apply a chemical resistant barrier cream to exposed areas of skin, such as wrists and forearms.

Precautions when using any treated timber

Users of any treated timber, regardless of the treatment type, should take certain health and safety precautions.

  • When power sawing or machining any timber (treated or not), wear goggles to protect eyes from flying particles and a mask to prevent dust inhalation.
  • If sawdust from treated timber gathers on clothes, wash them before reuse. Wash work clothes separately from other laundry.
  • After working with treated timber, avoid rubbing eyes or touching the mouth, and wash hands before eating, drinking or smoking.
  • Do not burn treated timber off-cuts and sawdust (such as for heating and barbecues).
  • Consult the local council about the proper way to dispose of treated timber waste.


Do not use treated timber for:

  • toys
  • items in contact with food or drinking water
  • wood shavings for animal litter or mulch.

If you experience health problems while using treated timber, review your health and safety precautions. If health problems persist, seek medical advice.

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This information is published by the Ministry of Business, Innovation and Employment’s Chief Executive. It is a general guide only and, if used, does not relieve any person of the obligation to consider any matter to which the information relates according to the circumstances of the particular case. Expert advice may be required in specific circumstances. Where this information relates to assisting people: