Victims of asbestos exposure today can still see their claim disputed by a former employer because of outdated research and misunderstanding over the risk level.

The fibres of white chrysotile, in particular, continue to be an asbestos awareness issue between those who say it is merely ‘low risk’ and requires only to be properly managed and others who state that any exposure to asbestos poses a potential health threat. Whenever white asbestos is discovered in a school premises or a council property, for example, a spokesman will issue a statement to reassure the local community that there is no health danger because the type of asbestos is of the low risk type.

Their assertion, which has also been used in court hearings, is likely to be based on the conclusions of historical clinical research. But the traditional guidelines, which determine the number of asbestos fibres found in a victim’s lung, known as the “lung burden” may not take into account other causal factors, such as the asbestos fibre type itself.

White asbestos fibres break down more easily

There is a critical difference between two types of asbestos fibres. The straight, needle-like structures of blue and brown asbestos fibres, which are classified as ‘amphibole’, embed themselves into the tissue of the lung linings and are almost impossible for the body to clear. However, the curly white asbestos fibres – known as ‘serpentine’ – are more able to be cleared by the body’s immune system over a shorter period.

Research found that white asbestos fibres break down more easily into smaller particles. As a result, they were not considered to be as likely to turn cells cancerous and spread to the lung cavity, where fatal mesothelioma tumours most commonly develop.

Less congested lungs also means that the body is also more easily able to clear out the longest fibres. So while there is evidence that heavy and prolonged exposure to chrysotile can and does produce lung cancer, it is argued that low exposures may not necessarily present a detectable risk to health.

However, much of the research was often based on asbestos exposure figures from the 1940s, 50s and 60s, obtained from heavy industries, such as shipbuilding, engineering and manufacturing where brown and blue asbestos was commonly used alongside white asbestos. While research studies concluded that about 20 million fibres were needed to be found in the lung tissue to be considered asbestos-related, there were cases where a significantly fewer number were found despite high, occupational exposure levels.

Counting of individual microscopic fibres

Judgements at court hearings are based on evidence produced confirming the link between a claimant’s level of asbestos exposure at a workplace contributing to the subsequent development of lung cancer or asbestosis disease. A medical report will include the counting of individual microscopic fibres found within the lung tissue.

However, the current accepted standard for the fibre count is increasingly being questioned. In 1997, a meeting comprising 19 delegates from eight countries was held in Helsinki, Finland, which saw the drawing up of a report recommending key “criteria” for use in the diagnosis and attributions of asbestos related illness.

The report highlighted research where the “lung fibre count exceeded the background range for the laboratory in question” and pointing out the results were “lower from the threshold value for persons with a high probability of exposure to asbestos dust at work…” Among the recommendations made in the report was that an important factor of asbestos exposure was the cumulative fibre dose expressed as ‘fibre years per cubic centimetre’.

Helsinki Criteria for fibre level

Later known as the “Helsinki Criteria”, the report set the fibre ml level at 25 fibre/ml years or above, at which asbestosis or lung cancer would be held to have been caused by asbestos exposure. The level of exposure would be determined on a scale from 1 year’s ‘substantial’ exposure at 25 fibre/ml through to 5 years ‘moderate’ exposure at 5 fibre/ml per year.

However, in a period of between 15 and 50 years, which elapses before asbestosis symptoms emerge, a greater number of white asbestos fibres would have actually vacated the body and the fibre count could then be as low as approx. 7 million.

In 2005, the Industrial Injuries Advisory Council (IIAC) relooked at the criteria by which specifically mesothelioma could “on the balance of probabilities” be attributed to asbestos, and the assumption that there was “a threshold of cumulative exposure, below which, clinical disease did not occur”.

A different formula for the calculation of risk

The criteria of ‘25 fibre years’ was seen as unlikely to be valid for all occupations. The Council obtained evidence that the risk of lung cancer varied between different industries at similar levels of cumulative exposure to asbestos. The cause could not entirely be explained by exposure to different asbestos fibre types as most workers were exposed to a mixtures of blue, brown and white fibres.

Furthermore, a different formula for the calculation of risk showed the difficulty of only using the first method for deciding attribution. The second method found that “a doubling of risk of lung cancer would be reached on average only after 100 fibre years asbestos exposure. The level of exposure required to double risk of lung cancer can be calculated as 25 fibre years or 100 fibre years depending on the risk formula used.

The IIAC cautioned that “a lack of asbestos fibres should not be used to exclude a diagnosis of asbestosis, as asbestos bodies may be absent and fibres not increased above background level in clear cut cases, i.e. where claimants have a history of “substantial occupational asbestos exposure”. The Council added that “counting techniques have a significant false negative rate”. The IIAC also recommended that a diagnosis of asbestosis should be based on clinical evidence of interstitial lung fibrosis and a history of substantial occupational exposure to asbestos.

Class 1 cancer-causing agent

As recently as May 2011, HM Government Office for Science said that it was “not possible to determine a threshold level”, below which, exposure to white asbestos could be considered safe for human health or change the classification as a Class 1 cancer-causing agent. In the same year, the UK was repeatedly called upon to comply with guidance set out by the European Asbestos Directive, which addresses the issue of “sporadic and low intensity exposure to asbestos” rather than simply measuring the extent of exposure and risk.

Victims will often recount their years of working in “clouds of dust” without a breathing mask or any personal protection equipment. The conditions can be clearly understood as a ‘substantial occupational exposure’ outside the narrow formula of a specific fibre ml threshold and which could deny a claimant to full damages.