size, density and consistency of the board. The boards are then cooled, trimmed and sanded. They can then be sold as raw board or surface improved through the addition of a wood veneer or laminate surface. Furniture design Particle board has had a huge influence on furniture design. In the early 1950s, particle board kitchens started to come into use in furniture construction but, in many cases, it remained more expensive than solid wood. A particle board kitchen was only available to the very wealthy. Once the technology was more developed, particle board became cheaper. Some large companies base their strategies around providing furniture at a low price. To do this, they use the least expensive materials possible. In almost all cases, this means particle board, medium-density fibreboard (MDF), or the like. However, in order to maintain a reputation for quality at low cost, manufacturers may use higher grades of particle board, e.g., higher density particle board, thicker particle board, or particle board using higher-quality resins. One may note the amount of sag in a shelf of a given width in order to draw the distinction. In general, the much lower cost of sheet goods (particle board, medium density fiberboard, and other engineered wood products) has helped to displace solid wood from many cabinetry applications. Safety Safety concerns exist for both manufacturing and use. Fine dust and chemicals are released when particleboard is machined (e.g., sawing or routing). Occupational exposure limits exist in many countries recognizing the hazard of wood dusts. Cutting particle board can release formaldehyde, carbon monoxide, hydrogen cyanide in the case of amino resins, and phenol in the case of phenol formaldehyde resins. The other safety concern is the slow release of formaldehyde over time. In 1984 concerns about the high indoor levels of formaldehyde in new manufactured homes led the United States Department of Housing and Urban Development to set construction standards. Particleboard (PB), medium-density fibreboard (MDF), oriented strand board (OSB), and laminated flooring have been major sources of formaldehyde emissions. In response to consumer and woodworker pressure on the industry, PB and MDF became available in "no added formaldehyde" (NAF) versions, but were not in common use . Many other building materials such as furniture finish, carpeting and caulking give off formaldehyde, as well as urea-formaldehyde foam insulation, which is banned in Canada for installation in a residential closed cavity wall. Formaldehyde is classified by