Dust: the hazards of RCS

I have long been concerned with the almost cavalier attitude to dust that is commonly adopted in the construction industry, for although no dust is totally harmless, exposure to respirable crystalline silica (RCS) is particularly problematic. An explanation for a large part of this problem with attitude to silica containing dust is ignorance of the true nature of the hazards associated with this material. That said the long history of respiratory disease associated with crystalline silica (commonly called quartz), shows that since the 1930s improvements in workplace standards of control have led to a marked improvement in ill-health statistics. Nevertheless, workers exposed to fine dust containing quartz (which is found in almost all kinds of rock, sands, clays, shale and gravel), are at risk of developing a chronic and possibly severe disabling lung disease known as silicosis (a form of fibrogenic pneumoconiosis) as well as the large numbers of people who die of other diseases such as bronchitis, emphysema etc. and the many cases of other types of  unspecified pneumoconiosis that are exacerbated by lung damage caused by prolonged exposure to dusty atmospheres. In addition, heavy and prolonged exposure to silica dust such as that found in quarries can lead to increased risk of cancer. There is also a possible association between silica exposure and scleroderma (an autoimmune disorder) and increased risk of kidney disease.

The HSE believe that in industries including construction, mining and quarrying, ceramics, heavy clay (brick and tile manufacturing), refractories, foundries and stonemasonry a least 100,000 workers are regularly exposed to RCS in industry, and many more are exposed on a less regular basis.

At this point it is salient to clarify the types of silicosis associated with differing levels of exposure, as although in general the disease manifests itself only after many years of exposure, high exposure over shorter periods can be equally devastating.

These forms are:

I have long been concerned with the almost cavalier attitude to dust that is commonly adopted in the construction industry, for although no dust is totally harmless, exposure to respirable crystalline silica (RCS) is particularly problematic. An explanation for a large part of this problem with attitude to silica containing dust is ignorance of the true nature of the hazards associated with this material. That said the long history of respiratory disease associated with crystalline silica (commonly called quartz), shows that since the 1930s improvements in workplace standards of control have led to a marked improvement in ill-health statistics. Nevertheless, workers exposed to fine dust containing quartz (which is found in almost all kinds of rock, sands, clays, shale and gravel), are at risk of developing a chronic and possibly severe disabling lung disease known as silicosis (a form of fibrogenic pneumoconiosis) as well as the large numbers of people who die of other diseases such as bronchitis, emphysema etc. and the many cases of other types of unspecified pneumoconiosis that are exacerbated by lung damage caused by prolonged exposure to dusty atmospheres. In addition, heavy and prolonged exposure to silica dust such as that found in quarries can lead to increased risk of cancer. There is also a possible association between silica exposure and scleroderma (an autoimmune disorder) and increased risk of kidney disease.

The HSE believe that in industries including construction, mining and quarrying, ceramics, heavy clay (brick and tile manufacturing), refractories, foundries and stonemasonry a least 100,000 workers are regularly exposed to RCS in industry, and many more are exposed on a less regular basis.

At this point it is salient to clarify the types of silicosis associated with differing levels of exposure, as although in general the disease manifests itself only after many years of exposure, high exposure over shorter periods can be equally devastating.

These forms are:

Simple Chronic Silicosis – silicosis resulting from long-term exposure to low amounts of silica dust. Symptoms include breathlessness similar to other forms of chronic obstructive pulmonary disease (COPD). Usually exposure is for more than twenty years.

Accelerated Silicosis - silicosis resulting from exposure to larger amounts of silica dust over a shorter period. Symptoms include lung inflammation and scarring. With an exposure of 5-15 years the disease progresses faster, causing weakness, a dry cough and weight loss often leading to death. 

Acute Silicosis – a rarer form of silicosis resulting from short-term exposure to very high amounts of silica dust, causing lung inflammation and pulmonary oedema resulting in shortness of breath and low blood oxygen.

None of these diseases are curable, and usually result in early death.

It should be remembered that excessive long-term exposure to any dust is likely to lead to respiratory (breathing) problems.

Though employers have a duty of care under the Health and Safety at Work Etc act 1974, and specifically must control exposure in accordance with COSHH Reg 7, Schedule 2A, the ACoP and relevant guidance, the level of workplace exposure clearly highlights the problems employers have in assessing the risk of exposure and putting adequate controls in place. 

Before going on to the hazardous effects of respirable silica which causes reportable illness and is the primary subject of this guidance, for the sake of clarity and in order not to minimise the hazards associated with all dust regardless of source or composition a short definition of the difference between inhalable and respirable dust and the standards associated with both is necessary is. The more stringent standard for respirable silica is discussed in more detail at a later stage.

Respirable dust standard

 'Respirable' dust has a technical definition and is the very fine dust which can be inhaled deep into the lungs. When exposures to respirable dust of any kind, including stone dust, exceed 4 mg/m3 (when measured or estimated for any 8-hour period) the COSHH Regulations apply. The 4 mg/m3 value is in effect a respirable dust standard. A similar logic applies to inhalable dust.

Inhalable dust standard

 'Inhalable' dust, like 'respirable' dust has a technical definition and consists of all sizes of particles which can be inhaled. Most of this dust is captured and removed by the body or is exhaled, being too large to enter the small air sacs in the lungs. By definition, inhalable dust also includes all respirable dust particles. When exposures to inhalable dust of any kind, including stone dust, exceed 10 mg/m3 (when measured or estimated for any 8-hour period) the COSHH Regulations apply.

 For employers this problem is further exacerbated by the changes to the Occupational Exposure Limit (OEL) for RCS.

A Maximum Exposure Limit (MEL) for RCS of 0.4 mg/m3 (8-hr Time Weighted Average (TWA) was introduced in 1992, replacing the earlier OES of 0.1 mg/m3.  In 1997, the value of the MEL was adjusted to 0.3 mg/m3 following adoption of the ISO/CEN EN481 sampling convention for respirable dusts. This change reflected a modification in measurement methodology, not an increased stringency of control. When the system of MELs and OESs was replaced by a new system with a single type of OEL known as a Workplace Exposure Limit (WEL), the MEL of 0.3mg/m3 for RCS was converted to a WEL of the same value. Following public consultation, a revised WEL of 0.1mg/m3 for RCS was adopted on October 1st, 2006.

Clearly this is an area where a level of expertise is required.

Most of the health effects listed here are due to regular and prolonged exposure over past decades. It is often assumed that modern working conditions are better, but this may not be so. It is possible that dust exposures have gone up in the last couple of decades with the introduction of electrically powered disc cutters etc., for in many circumstances cutting bricks, pavers etc. and chasing concrete etc is still undertaken dry, increasing the amount of dust created. It may be that silicosis and other adverse health effects will also rise.

Therefore, it is clear that the issue of dust is one to be taken seriously, and genuinely effective controls are needed when stone dust of any kind is concerned which includes materials such as sand, brick, and concrete. 

None of these diseases are curable, and usually result in early death. It should be remembered that excessive long-term exposure to any dust is likely to lead to respiratory (breathing) problems.

Though employers have a duty of care under the Health and Safety at Work Etc act 1974, and specifically must control exposure in accordance with COSHH Reg 7, Schedule 2A, the ACoP and relevant guidance, the level of workplace exposure clearly highlights the problems employers have in assessing the risk of exposure and putting adequate controls in place.

For the sake of clarity a short definition of the difference between inhalable and respirable dust and the standards associated with both is necessary is.

Respirable dust standard

 'Respirable' dust has a technical definition and is the very fine dust which can be inhaled deep into the lungs. When exposures to respirable dust of any kind, including stone dust, exceed 4 mg/m3 (when measured or estimated for any 8-hour period) the COSHH Regulations apply. The 4 mg/m3 value is in effect a respirable dust standard. A similar logic applies to inhalable dust.

Inhalable dust standard

 'Inhalable' dust, like 'respirable' dust has a technical definition and consists of all sizes of particles which can be inhaled. Most of this dust is captured and removed by the body or is exhaled, being too large to enter the small air sacs in the lungs. By definition, inhalable dust also includes all respirable dust particles. When exposures to inhalable dust of any kind, including stone dust, exceed 10 mg/m3 (when measured or estimated for any 8-hour period) the COSHH Regulations apply.

 For employers the problem of assessing and adopting the more stringent standard for respirable silica is further exacerbated by the changes to the Occupational Exposure Limit (OEL) for RCS.A Maximum Exposure Limit (MEL) for RCS of 0.4 mg/m3 (8-hr Time Weighted Average (TWA) was introduced in 1992, replacing the earlier OES of 0.1 mg/m3. 

 In 1997, the value of the MEL was adjusted to 0.3 mg/m3 following adoption of the ISO/CEN EN481 sampling convention for respirable dusts. This change reflected a modification in measurement methodology, not an increased stringency of control. When the system of MELs and OESs was replaced by a new system with a single type of OEL known as a Workplace Exposure Limit (WEL), the MEL of 0.3mg/m3 for RCS was converted to a WEL of the same value. Following public consultation, a revised WEL of 0.1mg/m3 for RCS was adopted on October 1st, 2006.

Clearly this is an area where a level of expertise is required.

Most of the health effects listed here are due to regular and prolonged exposure over past decades. It is often assumed that modern working conditions are better, but this may not be so. It is possible that dust exposures have gone up in the last couple of decades with the introduction of electrically powered disc cutters etc., for in many circumstances cutting bricks, pavers etc. and chasing concrete etc is still undertaken dry, increasing the amount of dust created. It may be that silicosis and other adverse health effects will also rise.

Therefore, it is clear that the issue of dust is one to be taken seriously, and genuinely effective controls are needed when stone dust of any kind is concerned which includes materials such as sand, brick, and concrete.