- High temperature insulation wools have been extensively tested for their potential health impacts.
- Consideration of all the available results indicates that dimension, durability and dose – the „3Ds“ – are important factors determining the ability of a fibrous dust to cause disease.
- The „3Ds“ allow us to compare different fibres in terms of their toxicological potency.
- Scientific knowledge about fibre toxicity has driven several initiatives by the industry to reduce potential risks in the workplace.
Driven by findings on the health effects of asbestos, extensive research has been conducted to evaluate the potential toxicity of many other fibrous materials.
This scientific research has used „in vitro“ testing (using cell cultures or simulated lung fluids), animal testing and epidemiological human studies.
As a result, it is now known that many types of dusts and fibres, reaching the gas exchange region of the lungs, can cause chronic inflammation. This may develop further into fibrosis (scarring of the lung tissue) which can cause, or predispose to, lung cancer.
Fibres passing into the lining of the chest cavity may also cause inflammation, fibrosis or tumours (mesotheliomas) at this site. Injecting fibres directly, into the abdominal cavity of rats can also cause mesotheliomas.
Consideration of all the available results indicates that three factors are important in the ability of a fibrous dust to cause disease. These are often called the „3Ds“:
Dimension
Fibre dimensions are critical, as only fibres of a certain size can reach the deep lung (the target organ). Mineral fibres with a diameter > 3 µm are, in humans, considered essentially „non respirable“, and for the rodents used in animal experiments fibres must be thinner still to reach the deep lung. While respirability is predominantly determined by fibre diameter, fibre length is also important. Short fibres behave as if they are compact particles and can be cleared by the normal mechanisms which involve cells in the lung called macrophages. However, long fibres frustrate this mechanism and are also, for some still unknown reason, more biologically active. This is also true both in tissue culture experiments and after injection – circumstances in which clearance mechanisms are not involved.
Durability
Durability in this context describes the ability of a material to persist in the lung and is more accurately referred to as „biopersistence“. There are several different mechanisms involved in the removal (clearance) of foreign particles from the lungs. Fibres can dissolve and/or they may break into shorter pieces which can then be removed by macrophages or be transported through the lymphatic system. The rate of removal of different fibres, typically measured in animal experiments, is expressed as the „half life“ – that is the time it takes for the number of fibres in the lungs to reduce by 50%.
Dose
The last „D“ – dose – is related to the other two parameters and is often referred to as „lung burden“. With chronic exposures the lung burden is the result of ongoing deposition (determined by workplace exposure levels and fibre dimensions) and clearance (determined by fibre biopersistence). If the exposure is high enough and clearance slow then a sufficiently large dose may accumulate and adverse health effects occur.
The scientific knowledge about fibre toxicity – summarised in the 3D approach – allows us to compare different fibres in terms of their toxicological potency, and has driven several initiatives to reduce potential risks in the workplace. This risk reduction can be achieved by:
- The development of thicker fibres. If a fibre is thick enough to be non-respirable, respiratory health effects are eliminated. This approach has its limitations as the insulation properties of thicker fibres are less favourable and thicker fibres are more likely to cause „itching“ (mechanical skin irritation).
- The development of less biopersistent fibres. This approach was the foundation of the development of AES wools which are cleared rapidly from the lung.
- Development and implementation of industrial hygiene practices and exposure controls. One way to manage risk in the workplace is by reducing the level of exposure to any potentially hazardous material. ECFIA has developed handling advice and guidelines based on many thousands of exposure measurements in their CARE programme. ECFIA members are therefore well placed to help their customers minimise workplace exposures and hence reduce possible risks.
Overload and its possible consequences
Survey of the Biological Effects of Refractory Ceramic Fibres.