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What is silica?

Silica is one of the most common naturally occurring elements on the planet. Silica, the mineral compound silicon dioxide (SiO2), is found in two forms -- crystalline or noncrystalline (also referred to as amorphous).

Silica is commonly found in most rocks and sand, and in products such as bricks, concrete, ceramics, clay, glass, pottery and electronics.

Typical industries where exposure is likely to occur are cement manufacturing, glass / concrete mixing product manufacture, foundries, sand-blasting, manufacturing of abrasives, and many construction activities. In construction these materials create dust when they are cut, sanded, carved etc. Some of this dust may be fine enough to breathe deeply into your lungs.

What are the health effects?

Inhaling silica dust can lead to serious, sometimes fatal illnesses including silicosis, tuberculosis (in those with silicosis), and chronic obstructive pulmonary disease (COPD). Silica in its crystalline form has recently been classed as a respiratory carcinogen as it causes occupational cancer.

Respirable silica, which is the fine fraction of the dust (<2.5 microns) is too small to see with normal lighting. The amounts needed to cause ill health are not large, and are 100x less than the general dust exposure.

Silica related illness as a results of low concentration exposure can take up to 10 years to occur, but in circumstances where exposures are high symptoms can develop within a few weeks.

What are the legal exposure limits?

British occupational exposure limits (WEL’s) are set to help protect the health of workers. WEL’s are concentrations of hazardous substances in the air, averaged over a specified period of time.

Legal exposure limits have been set by the Health & Safety Executive for the following forms of silica:

• Amorphous Silica 6mg/m3 (inhalable) & 2.4 mg/m3 (respirable)
• Crystalline Silica 0.1mg/m3, classified as a carcinogen (respirable)
• Fused Silica 0.08mg/m3 (respirable)

In circumstances where work involves activities that lead to exposure to a carcinogen, all reasonable efforts must be made to reduce exposure to levels as low as possible regardless of the measured exposure in relation to the WEL.

Assessing the risk from this type of exposure should take into consideration the fact that any measurements obtained require a specific sampling and analysis technique (X-ray powder diffraction) different to general dust monitoring used for low toxicity dusts.

What actions do I need to take to meet the regulations?

Employers must comply with The Control of Substances Hazardous to Health Regulations 2002 and need to:

• Assess the risks to health via a risk assessment
• Keep a written record of the risk assessment if they employ more than five people
• Communicate details about anything significant risks to staff
• Consider where practicable substituting material with a lower silica content
• Utilise mechanical controls such as local exhaust ventilation
• Where necessary, provide staff with personal protective equipment
• Maintain all equipment used as control measures in good working order
• Instruct and train staff to use equipment properly
• Monitor to ensure that controls are effective and that the WEL’s are not exceeded
• Arrange health surveillance of the workforce

How should the effectiveness of controls be monitored?

Because of variations in plant, process, work and other conditions it is difficult to draw conclusions about long-term exposure patterns on the basis of a single measurement of exposure at one point in time.

Exposure monitoring should be carried out on at least an annual basis depending on the risk identified from your initial assessments. The frequency will vary and should depend on how close the measured exposure is to the workplace exposure limit, significant or highly significant exposure scenarios should be measured more frequently.

A regular monitoring program is required for the following reasons:

• to ensure that the health of the workers is efficiently protected;
• to ensure that the preventive actions which have been taken are still effective;
• to ensure that the levels, as measured previously, remain unchanged or fall;
• to ensure that any changes made in manufacturing processes or work practices will not lead to an excessive exposure to hazardous substances;
• to promote the implementation of more efficient preventive measures.
  for insurance purposes

Employers must keep a record of monitoring carried out for at least 5 years, or for 40 years for personal exposures of identifiable employees.

Should I carry out personal or background monitoring?

Personal monitoring should always be the first choice!

Personal monitoring should be used to evaluate the risk of exposure to the individual worker. Air samples should be collected in the workers breathing zone by means of personal samplers. Sampling should be carried out while the work activity is in operation.

Where concentrations vary from one work operation or phase to another, personal sampling should be done in such a manner that the averages and in any case the maximum, level of exposure of each individual worker can be determined.

Exposure profiles of particular jobs or occupational categories should be constructed from the air-sampling data of different operations and from the workers' exposure time in these jobs.

If background monitoring is to be carried out it should only be used to determine the distribution of airborne substances throughout the general atmosphere of the working area and to identify problems and priorities. This form of sampling can not be used to compare exposures against legal exposure limits.

How Many Staff Should be Monitored?

Taking one or a few samples on one day will not provide you with sufficient information on which to base conclusions about long-term exposures. In reality the number of samples that you can take is usually constrained by the resources available to you. You need to use your judgement when deciding on sample size, especially when small groups are concerned.

For worst-case monitoring, as a rule of thumb, at least one employee in five needs to be monitored from a properly selected similar exposure group (SEG), unless a smaller number can be justified.

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