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Tackling the respirable hazards of crystalline silica in construction and related industries

23 January 2013

For workers in professions such as construction, abrasive blasting, quarrying and stonemasonry, some of the safety hazards and risks of injury are obvious. Significant occupational health hazards are also posed to the r

For workers in professions such as construction, abrasive blasting, quarrying and stonemasonry, some of the safety hazards and risks of injury are obvious. Significant occupational health hazards are also posed to the respiratory system, however. These hazards are less obvious and health effects can occur over longer periods of time if correct controls are not in place.

Dust is generated when workers chip, cut, drill or grind stone and rock and in many cases this dust is created from a base material which contains crystalline silica.

The dust may initially look innocuous, but respirable crystalline silica can cause disabling illnesses and may even in the most serious cases result in cancer1.

Indeed, some 789 deaths from lung cancer were attributed to silica in a 2010 Health and Safety Executive Research Report, while there are more deaths due to silica in the construction industry than in any other sector2.

What is crystalline silica? Crystalline silica is a fundamental constituent of soil, sand, granite and many other minerals. It is used as a raw material in many processes and is found in a wide range of building materials, such as kerb stones and tiles. It is most commonly found in quartz but is also in other minerals such as cristobalite and tridymite. When materials containing crystalline silica are crushed, cut or abraded, respirable crystalline silica may be released.

If inhaled, respirable crystalline silica can penetrate deep into the lungs, causing scar tissue to form and hindering the lungs' capacity to absorb oxygen - a condition called silicosis.

What are the main health problems? The diseases associated with exposure to respirable crystalline silica are exceptionally unpleasant and, as well as silicosis and lung cancer, include chronic obstructive pulmonary disease (COPD).

Silicosis can occur in two main forms depending upon the duration of the exposure and the concentration of silica.

The most common form is chronic silicosis, caused by prolonged exposure to medium to low concentrations of silica, with symptoms ranging from fatigue and shortness of breath to chest pain. Chronic silicosis can be extremely disabling and may lead to premature death3.

Acute silicosis is caused by excessive contact with exceptionally high concentrations of silica, and symptoms can present after only a few months.

These include severe, disabling shortness of breath, weakness and weight loss, which can be fatal 4.

Lung cancer is the most common form of cancer-related death and exposure to silica is the second largest cause of occupational lung cancer, second only to asbestos2. Its symptoms include shortness of breath, coughing blood and weight loss. While it is widely associated with smoking, there is some evidence that suggests that lung cancer is even more common in smokers who are exposed to silica.

COPD is the name given to a number of lung conditions, including chronic bronchitis and emphysema, which prevent the sufferer from breathing properly. As the condition progresses, this worsens and can become extremely debilitating. The symptoms of COPD are similar to those of asthma but while asthma can be controlled, once COPD develops the damage to the lungs cannot be reversed5.

Who is affected and where? Exposure to silica occurs in multiple construction operations - these can range from cutting paving stones and kerbstones with rotary cutters, through to abrasive blasting with sand to remove paint from concrete structures and other surfaces. Other operations which may result in contact include using pneumatic drills, rock drilling, concrete mixing, concrete drilling, demolition and tunnelling operations.

Silica exposure is also an issue in cement and brick manufacturing, china and ceramic manufacturing, and the steel and foundry industries. Meanwhile, exposure can occur in the maintenance, repair and replacement of refractory brick furnace linings.

What does the law say? Exposure to respirable crystalline silica (RCS) is governed by the Control of Substances Hazardous to Health Regulations (COSHH).

The Workplace Exposure Limit (WEL) for respirable crystalline silica is 0.1mg/m? averaged over an eight-hour period and legally, exposure levels must not exceed this limit.

Over a period of 15 years, even at this daily exposure limit, workers still have a one in 40 chance of developing silicosis.

Reducing the exposure level to approximately half this amount cuts the risk by five times. However, exposure at three times the limit would increase the risk of developing silicosis by eight times6.

It is because of these risks that the Health & Safety Executive (HSE) states that, for the construction industry, exposure to silica must be controlled to as far below the WEL as is reasonably practicable.

Managing exposure There are three steps to which employers should adhere in the hierarchy of control in order to minimise exposure to hazardous substances. The first is the elimination or substitution of working methods and materials, followed by engineering controls. Both of these must be thoroughly explored before the final step - the use of personal protective equipment (PPE) - is considered.

The first step requires employers to establish whether or not the product containing the hazardous substance, or the process generating it, can be eliminated or substituted. For silica, this might involve using a material containing less, or ideally zero, silica, or eliminating the need for cutting kerbstones, for example, by using pre-cut products.

The next step is to use engineering controls. For indoor processes, these can include local exhaust ventilation. For other processes, such as cutting kerb stones, the HSE requires the use of water suppression. Finally, PPE may be used if required to reduce exposure to acceptable levels.

In its latest guidance for the control of silica dust in the construction industry, the HSE goes even further, stating that respiratory protective equipment (RPE) must be worn in addition to other control measures.

Specifying and selecting RPE Specifiers can select from disposable, halfmask, full-face or powered respirators depending on the level of exposure, identified through risk assessment, nature of the task and personal preference.

Disposable respirators are available in three levels of protection - FFP1, FFP2 and FFP3. The HSE guidance for silica dust requires the use of respirators with an assigned protection factor (APF) of at least 20 - this means that exposure is reduced by at least a factor of 20 when the product is face fit tested and worn properly by a trained user. If a disposable respirator is preferred an FFP3 respirator should be selected.

Many disposable respirators are 'single shift' products and so should not be used for more than day, while others have cleanable face seals making them suitable for limited re-use if kept in a good condition. Products which are suitable for limited re-use will be marked "R", while those which are for single use only will be marked "NR" as dictated by the European Standard EN149:2001+A1:2009.

Disposable respirators come in a variety of shapes and sizes, from cupshapes to 'fold flat' to meet individual preferences. While the majority of products have fixed length straps, some come with adjustable straps to help accommodate different face shapes.

Reusable half-mask and full face respirators consist of a facepiece and replaceable filters which can be reused for days or even weeks before needing to be changed. When fitted with a P3 particulate filter, a half-mask offers an APF of 20, while a full face mask offers an APF of 40. The filter needs to be changed when the wearer experiences increased breathing resistance.

Reusable respirators to must be maintained if they are to offer effective protection. Maintenance includes pre-use and post-use checks, care and maintenance, and consumable replacement when necessary. Appropriate storage when not in use is also important.

Disposable and reusable half-masks and full face respirators are classed as 'tight fitting' respirators and before first use, it is a legal requirement to conduct a fit test.

There are two types of fit test - qualitative (suitable for disposable respirators or half-masks) and quantitative (suitable for full face respirators including full facepieces fitted to a negative pressure or powered or positive pressure device). Fit testing gives an assessment of facial fit to an individual RPE wearer. Quantitative testing gives a fit factor (an actual number), while qualitative provides a pass or fail result.

It should also be remembered that wearers of tight fitting respirators must be clean shaven, not only on the day of the fit test but every time they use the product. Even a small amount of stubble can affect the quality of the seal to the face.

Employees should be instructed to fit the respirator well, to perform all necessary fit checks before entering the affected area and not to remove it in the hazardous environment. Removing the respirator even for a few minutes can dramatically affect the level of protection offered.

The role of powered respirators Powered air respirators have a higher unit cost but are frequently considered a more comfortable option for wearers working in hot or humid conditions, or whose work is physical or lasts a long time. They offer high levels of respiratory protection and are also available with integrated head, eye and face protection which can overcome the problems of PPE compatibility. Powered air respirators are loose-fitting, meaning the face seal is less critical than with tight-fitting respirators and fit testing is not required.

As with reusable respirators, powered air respirators must be well-maintained with regular checks. Monthly records must be kept and able to be produced on demand at an HSE inspection.

As well as providing RPE and training in its use, employers must ensure that correct work methods are followed and that an appropriate health surveillance programme is established.

Training employees The HSE requires that wearers of PPE are trained in its use and it is recommended that workers who may be exposed to silica are trained on its potential health effects and how exposure might be controlled.

Training may include: How to conduct the task in a way which minimises exposure The use and maintenance of dust suppression and extraction equipment Care and maintenance of PPE, including storage How and when to wear PPE, including correct fitting and use.

Keeping surfaces clean as this helps prevent dust becoming airborne again.

3M is featuring an articulated presentation on Silica on its segment page www.3M.co.uk/construction. The company also offers a number of services, including quantitative or qualitative fit testing. For product and support information call 0870 80 800 60 in the UK or 1 800 320 500 in Ireland. For more information on 8300 series disposable respirators and free product samples, visit www.3M.co.uk/comfortcounts.

For more information please visit www.3M.co.uk/ohes.

References 1. http://www.hse.gov.uk/quarries/silica.htm. Viewed18/10/2010 2. HSE Research Report 800, The Burden of Occupational Cancer in Great Britain (2010).

3. http://www.hse.gov.uk/construct