In your article "Voyage to the centre of the Earthship" (3 February), you stated that the cement industry's use of tyres to replace fossil fuels in kilns results in production of "undesirable emissions". This is untrue.

The article is correct when it states that discarded tyres in landfill are not biodegradable and that toxic chemicals can leak and pollute water supplies. However, rather than just burning such materials in an incinerator, a cement kiln recovers tyres' energy content.

Because energy recovery in the kiln takes place at temperatures of 1400°C, the rubber and fabric elements of the tyres are completely consumed without any of the black smoke and smell associated with burning them on a bonfire. There is also no ash left for subsequent disposal.

The use of tyres and other waste products as replacement fuels also reduces the emissions of sulphur dioxide, oxides of nitrogen and particulates from the kiln, and contributes to the reduction of carbon dioxide. The net effect is environmental improvement. The environmental impacts from cement makng are closely regulated by the Environment Agency, which will not permit the use of waste-derived fuels if there is an adverse effect on the environment.

Mike Gilbert, chief executive, British Cement Association