The collapse of an East Cheshire indoor market roof suspected of containing asbestos is the latest reminder that the historical risk of exposure is still very much with us today.

It may be supposed that the potential risk from the 20th Century’s most deadly insulation material is confined to schools, council premises and former factory buildings. It is clearly not the case, and our asbestos awareness to the ever-present dangers is raised every time a case is reported.

The recent heavy rainfall is said to be the cause of the collapse of the roof at the indoor market in Sandbach, Crewe, which led to its temporary closure. Throughout much of 2016, as in previous years, unusually severe rainfall and flooding has led to an increased risk from damaged asbestos roofs that still cover all types of public, or residential buildings.

More than a half (55 per cent) of all industrial or commercial properties in the UK have an asbestos cement roof and three quarters still cover the structures where they were built, according to the Land Registry. Half a million properties around the UK are also likely to still contain hidden asbestos materials, according to the Health and Safety Executive (HSE). The safety watchdog also estimate that around 1.8 million people across Britain are still in danger of breathing in the deadly fibres, and at least 2,000 cases of asbestos-related mesothelioma cancer are diagnosed each year.

Asbestos cement widely used in corrugated sheeting

The professional construction industry repeatedly warn that asbestos-containing materials are likely to be present in any public, private or commercial property built or renovated up until 2000. The relatively recent ‘cut-off’ date is based on the introduction of a ban on white asbestos fibre types in the last weeks of 1999. Up until this time, between 10 and 15 per cent of white chrysotile asbestos fibres continued to be used in the reinforcement of building insulation products made of cement.

The weatherproof properties of asbestos cement meant it was widely used in the production of corrugated sheets, slates and soffits, sills, copings, chalkboards, fascias, infill panels, etc. Following the first ban on the most dangerous blue and brown asbestos types in the mid-1980s, builders could still be using their stock holding of white ‘chrysotile’ insulation and fireproof materials for at least another ten years.

Often the inside of an asbestos cement roof will be lined with plasterboard or fibreboard panels where the paper lining is found to be made from 100 per cent white chrysotile asbestos. In some buildings it has been discovered that the lining panels were made from brown ‘amosite’ asbestos or with both amosite and blue ‘crocidolite’ asbestos.

A damaged, leaking or otherwise weakened roof will also affect the internal lining panels and cause the fibre dust particles to break off and disperse into the surrounding atmosphere. This might occur even when the asbestos materials are normally considered relatively safe because the fibres were originally factory bonded to the cement.

Bonded material can still break down

Hard-bonded asbestos was the most commonly found form of asbestos used in flat, corrugated or compressed asbestos-cement sheeting on garage roofs. However, when subject to prolonged and severe conditions of extreme weather or temperatures, the integrity of the material encapsulation can still break down, which could result in the release of asbestos fibre dust.

An asbestos management review carried out in 2011 advised that there should be a reassessment of the potential risk posed by ‘bonded’ asbestos when subject to flooding, fire, high temperatures, as well as other categories of severe damage caused by extreme weather or natural disaster.

The dull grey, corrugated asbestos cement roof may not be easy to distinguish from a non asbestos corrugated roof after years of weathering have taken their toll. In most cases, the roof may be completely covered in dark green moss or lichen, heavily stained or bleached out. Furthermore, it is likely that aging has caused structural deterioration, and the roof has become porous and prone to leaks.

Under the Control of Asbestos Regulations 2012, asbestos surveys are required to be carried out in advance of renovations or demolition of premises. Properties with severe structural damage could require an authorised and licensed asbestos removal of any asbestos-containing materials from the debris rather than attempt to clear potential hazardous waste by the property owner or tenant.