Why is MDF so toxic?

hse.gov.uk - Frequently Asked Questions - MDF - HSE

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Medium Density Fibreboard (MDF)

Q1. What is MDF?

Medium Density Fibreboard (MDF) is an engineered wood-based sheet material made by bonding together wood fibres with a synthetic resin adhesive. MDF is extremely versatile and can be machined and finished to a high standard. As a result, MDF has replaced solid timber as a low-cost alternative in a wide range of applications across industry. The majority of MDF is mainly composed of softwood, although some brands may contain a higher percentage of temperate hardwood if this is locally available to the manufacturer. High levels of hardwood can be found in MDF board from outside the UK and Ireland. The most common binder for boards intended for dry environments is urea-formaldehyde. Other binders may be used depending on the grade of board and its intended end-use. For example, melamine urea-formaldehyde, phenolic resins and polymeric diphenylmethane diisocyanate (PMDI) are generally used in boards that require an improved moisture resistance. PMDI binder is not formaldehyde-based and consequently does not emit any formaldehyde. The exact constituents of an MDF board will vary from product to product.

Q2. What are the dangers of working with MDF compared with softwoods, hardwoods or other panel products?

The atmosphere created by machining or sanding MDF board contains a mixture of softwood dust and hardwood dust (if it is present). In addition, there will also be free formaldehyde, dust particles onto which formaldehyde is adsorbed and potentially, the resin binder itself and its derivatives. However, the levels of free formaldehyde in boards made within the EU at levels of formaldehyde class E1 are thought to be insignificant. This is because at these levels the resin is fully reacted (polymerised) – see Q.4 & Q.5 for information on standards and classes. Under current legislation softwood dust, hardwood dust and formaldehyde are considered to be hazardous to health. Both softwood and hardwood dusts are known to be respiratory sensitisers and may cause asthma and other respiratory problems. Hardwood dust can also cause a rare form of nasal cancer. Formaldehyde is classified in the UK, and in the European Union as a carcinogen and it carries the hazard statement 'suspected of causing cancer'. Because of the additional presence of formaldehyde in MDF the simple precautions detailed in Q.7 and Q.8 should be followed.

Q3. What is formaldehyde and where does it come from?

Formaldehyde is a simple but essential organic chemical that occurs naturally in most forms of life, including people, some foods we eat and trees. All products made from wood will therefore emit some naturally occurring formaldehyde. It is widely used in the manufacture of numerous products including shampoos, plastics, carpets, clothing, resins and glues etc. A range of materials found in the home or workplace may therefore release formaldehyde. The US Consumer Products Safety Commission provides the following information on formaldehyde on their website. Formaldehyde is normally present at low levels, usually less than 0.03 ppm,(parts per million) in both outdoor and indoor air. The outdoor air in rural areas has lower concentrations while urban areas have higher concentrations. Residences or offices that contain products that release formaldehyde to the air can have formaldehyde levels of greater than 0.03 ppm. Products that may add formaldehyde to the air include particleboard used as flooring underlayment, shelving, furniture and cabinets; MDF in cabinets and furniture; hardwood plywood wall panels, and urea-formaldehyde foam used as insulation. Similar levels are quoted in the World Health Organisation (WHO) report WHO guidelines for indoor air quality: selected pollutants, published in December 2010. This states for buildings, some of which contain wood based panels, 'levels on the average are less than 0.05 mg/m3 (0.04ppm) in homes and about half that in public buildings'. It is important to note that these levels are from all sources, not just building products.

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Q4. How much formaldehyde is released by MDF board?

MDF boards manufactured in Europe for construction purposes must meet the appropriate European standards. These are BS EN 622-1:2003 Fibreboards-Specifications - Part 1: General requirements and BS EN 622-5:2009 Fibreboards - Specifications - Part 5: Requirements for dry process boards (MDF). There are two European formaldehyde classes, E1 and E2, depending on levels of formaldehyde emission measured. The release of formaldehyde from E1 boards is less than 0.1 ppm (parts per million) and for E2 boards it is between 0.1 ppm and 0.3 ppm. In Europe, the majority of manufacturers produce only low emission boards. There are some boards available on the market with extremely low formaldehyde emissions and some with 'no added formaldehyde', for example those using formaldehyde free binders such as PMDI, ie these boards will only have the naturally occurring emissions from the wood itself. Manufacturers from outside Europe may however produce boards that have higher emissions.

Q5. How are MDF boards labelled?

Wood based panels, such as MDF, that are used in construction should be CE marked according to – Characteristics, evaluation of conformity and marking. In complying with this standard, formaldehyde levels will have to be tested on a regular basis and a class will have to be declared (E1 or E2). Other than compliance with the Construction Products Directive via CE marking (soon to be superseded by the Construction Products Regulation), there are no regulatory compliance schemes in the UK for emissions of formaldehyde. There are a limited number of third party labelling schemes that do operate in the UK which specify amongst other things, maximum formaldehyde limits as part of their requirements. Such schemes include BREEAM (Building Research Establishment Environmental Assessment Method) for the assessment of buildings and for furniture products and the Furniture Industry Research Association 'FIRA Gold' scheme.

Q6. Is MDF banned in other countries and, if so, why not in the UK?

HSE is not aware of any countries in the world where MDF is banned.

Q7. What precautions should be taken when working with MDF?

Employers have duties under the Control of Substances Hazardous to Health Regulations 2002 (COSHH) to control risks to employees' health arising from work activities. This means they need to ensure exposures to wood dust and formaldehyde are kept as far below the Workplace Exposure Limits (WELs) as reasonably practicable. WELs are the concentrations of hazardous material in the air averaged over a specified time period – called the Time Weighted Average (TWA). Two periods are used, long-term (8 hours) and short-term (15 mins) – the long-term representing a working day and the short-term to help prevent effects such as eye irritation which may occur after only a few minutes exposure. The WELs for hardwood dust, softwood dust and formaldehyde are expressed in the number of milligrams (mg) of material in one cubic metre of air (m3). Levels of formaldehyde are also expressed in parts per million (ppm). The current WELs are: Formaldehyde - 2.5 mg/m3 or 2 ppm for both the long-term exposure limit and the short-term exposure limit

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2.5 mg/m3 or 2 ppm for both the long-term exposure limit and the short-term exposure limit The WEL for hardwood dust is 3mg/m3 (based on an 8-hour time-weighted average). The WEL for softwood dust is 5mg/m3 (based on an 8-hour time-weighted average). For mixtures of hardwood and softwood dusts the WEL for hardwood dust of 3mg/m3 applies to all wood dusts present in that mixture. There is no short-term WEL To control exposures, employers should follow the 'hierarchy of control' set out in the COSHH Regulations. This means: First, try to reduce risks at source where possible by using a lower risk alternative, where one exists. An example of this could be to use a 'no added formaldehyde' MDF board or low-emission MDF board if practicable to do so. There should be an effective dust extraction system in use whenever MDF is machined or sanded. This is often termed local exhaust ventilation (LEV). Use vacuum cleaners with high performance filters (HEPA) to clean up MDF dust, or use a hose connected to the LEV system. Airlines and brushes should not be used as these produce clouds of fine dust that is easily breathed in. Respiratory protective equipment (RPE) may also be needed but this will generally be the last line of protection, see Q.8.

Q8. If I do need to use respiratory protective equipment (RPE), what should I use – is a dust mask sufficient?

RPE should not be used as the only means of control as it should complement other control measures such as a dust extraction system. General information on RPE is available at respiratory protective equipment at work: A practical guide. When you need to use RPE to provide protection against inhalation of wood dust, you should ensure that the RPE is adequate and suitable (for more information see selecting suitable respiratory protective equipment).

In summary:

For RPE to be adequate you must select the right mask/respirator and filter. A face filtering piece (FFP) with an assigned protection factor of at least 20 eg FFP3 or a half-mask with a P3 particle filter can be used to protect against exposure to wood dust. Do not use nuisance dust masks, FFP1 or FFP2 as they do not provide sufficient protection. If organic vapours are also present eg formaldehyde, then a half-mask with both a P3 particle filter and an appropriate filter for the organic substance could be used. For RPE to be suitable it must fit the wearer and be appropriate for the task and environment. For tight-fitting masks like a dust mask you must ensure that the mask fits the worker by undertaking 'face fit' testing (for further details see Guidance on respiratory protective equipment (RPE) fit testing). Workers wearing tight-fitting masks must be clean-shaven as stubble prevents the mask sealing properly against the face. The mask worn should be compatible with any other protective equipment worn eg safety glasses, hearing protection. Any RPE should be used correctly, and filters changed regularly, in accordance with the manufacturers instructions. Respirators must also be stored correctly and, for non-disposable RPE like half-masks, properly maintained by a competent person.