Last reviewed 5 December 2016
Working with rock, soil and concrete exposes many workers to silica dust, one of the UK’s five big industrial lung cancer killers. Jon Herbert looks at how hundreds of lives can be saved annually.
Silica dust is responsible for some 800 industrial deaths a year. The Health and Safety Executive (HSE) ranks it as the largest risk to construction workers after asbestos. With some 900 new cases reported annually, survival rates are low.
However, initiatives to eliminate fatalities caused by inhaling respirable crystalline silica (RCS) — otherwise known as stone dust — are taking place on several fronts. These include raising awareness, new guidelines, scientific breakthroughs and more good practice.
The first is a major drive from the Institution of Occupational Safety and Health (IOSH) which should result in a new cross-industry approach to mineral dust control at work. It is supported by the HSE, trade unions and business.
IOSH’s “No Time to Lose” occupational cancer campaign now includes detailed guidance on the dangers of “dust” and how it can, and should, be avoided.
As Executive Director of Policy, Shelley Frost points out in the case of silica, “dust is not just dust” and is likely to contain a range of potentially harmful substances that can cause chronic illness.
However, as Ms Frost also explains, many good practice examples are available to help mitigate the threat. IOSH wants to break down barriers so that essential information is shared with everyone affected directly, or in a position to protect others who may, or may not, realise they are at risk.
“No Time to Lose” focuses on the main causes of occupational cancer, those being silica dust, asbestos, diesel engine exhausts, solar radiation, plus shift work that impairs human immunity systems.
A second development announced in November 2016 is a research breakthrough which may have pinpointed exactly why silica poses such an active health hazard.
Russian scientists working at three Moscow research centres — LPI RAS, Skoltech, and Moscow Institute of Physics and Technology (MIPT) — have reported discovering unusual properties of silicon nanoparticles which make silica dust so dangerous. Their work shows that under normal conditions, silica nanoparticles become enriched with oxygen. These contain what are known as reactive oxygen species. Their presence may explain the high toxicity and carcinogenicity of silica dust. The main offenders are peroxo- and ozonide ions and oxo-radicals, all of which are highly reactive with biomolecules.
Silicon nanoparticles oxidise in the presence of oxygen, although exactly how it is still unclear. Detailed work by the researchers has shown that under normal atmospheric conditions they exist not in the expected composition SiO2 suggested by classical chemistry, but in an oxygen-enriched form with magnetic properties and the ability to form carcinogenic compounds. Research continues.
The hazards of silica
Silica, or quartz, is a natural and very common mineral found in soil, sand, concrete, bricks, fibre, cement products, masonry, rock, granite, clay and landscaping materials. Sandstone is more than 70% silica; granite 15–30%.
Cutting, grinding, sanding, sawing, drilling, loading, transporting, dumping or simply disturbing these materials can release very small crystalline silica particles invisible to the naked eye. These are easy to breathe deep into the lungs. Even small amount of airborne silica dust can contribute to the formation of lung disease and lung cancer.
Demolition is another very common source of dust, as is abrasive blasting with sand as the abrasive. The dry sweeping, or pressurised air blowing, of concrete and rock should be avoided.
The Control of Substances Hazardous to Health Regulations 2002 (COSHH) governs responsibilities in exposure to silica dust at work.
Silica dust can lead to extremely serious health problems. The HSE has estimated that more than 500 construction deaths in 2005 were the result of historic RCS inhalation.
Silicosis is caused by breathing in silica dust which scars lung tissue and results in lost lung function characterised by breathlessness. The effects are permanent and can continue to develop even after exposure ends. Follow-on impacts can be an increased risk of kidney disease and tuberculosis.
Chronic obstructive pulmonary disease (COPD) refers to another chronic lung condition that creates breathing difficulties. COPD is associated with some 4000 deaths linked to past silica exposure.
Lung cancer can result from lengthy exposure to high levels of silica dust. Once silicosis has been diagnosed, lung cancer risks increase.
It is important to note, however, that lung disease can be caused by both long-term exposure to small or moderate levels of silica dust, and short-term exposure to high levels. Smoking increases the dangers.
Employers have a legal duty to take all practicable steps ensuring employee safety at work by eliminating, isolating or minimising silica dust in the workplace. Planning is important. Where silica dust is present, the process should include control methods which are covered in this feature, ie: respiratory protection; air monitoring; health monitoring; protective clothing; warning signs; and training.
Prevention and minimising silica dust in the workplace
The key is to prevent silica dust from becoming airborne.
Water, and wet working methods, can keep silica dust out of the air and lungs of workers. Water hoses should be available to wet any dust created before it becomes airborne and used rather than compressed air. It is vital not to dry sweep. Dust must be removed using vacuums with high-efficiency particulate air (HEPA) filters.
Equipment and work areas need frequent cleaning. For example, saws used on concrete and masonry can be fitted with water to the blade; earthmoving equipment should have dust collection systems and air-conditioned cabs with a filtered air supply.
Metallic shot, slag products, or grit should be used for abrasive blasting, with abrasive containment methods.
It is important that workers use these systems routinely and correctly.
Certified respirators are important but not a primary way to prevent exposure to silica dust.
Selecting the correct respirator is essential and can take the form of a disposable, half-face, full-face (with filters) or full-face powered unit (supplying clean air).
Disposable respirators must fit securely; a clean shave is advisable. In construction, disposable or half-face respirators often provide sufficient protection. During abrasive blasting, airline respirators are needed.
Maintenance is also vital, as is training, keeping usage records and storing respirators in a clean environment.
Air monitoring should measure overall silica dust quantities around the worksite and maximum worker exposure levels. Monitoring will also help in the selection of dust control methods and protection. Health monitoring of all workers exposed to dust is important too.
Dusty clothes should not be allowed to contaminate cars, homes and other areas away from the workplace. Disposable or washable clothes are advisable, as is making sure that employees can shower, or wash with water, and change into clean clothes before leaving work. Contaminated clothing should be washed but not taken home.
Risk area boundaries should be signed, with advice shown on the use of protective equipment.
Training must include information about silica dust health effects, work practices and the use and care of protective equipment.
The HSE has a codified approach to managing health issues such as silica dust exposure which it summarises as:
Who does what?
Everyone has a role to play in silica dust safety, including clients, designers in the pre-construction phase, contractors and individual employees.
The aim is to manage risks rather than lifestyles and involves a four-step assessment process.
Plan — your overall strategy.
Identify — health hazards linked to your work.
Assess — the significance of these hazards.
Involve — workers in managing health risks.
Preventing ill health then depends on putting plans into action.
Prevent — risks before work starts.
Control — any remaining risk.
Train — workers.
The last priority is to manage risks and not symptoms. To ensure controls are working, the following review steps are important too.
Supervise — workers.
Maintain — controls.
Monitor — controls to ensure they are effective.
Act — to put any problems right.
As silica dust is regarded as being the second biggest industrial killer, it is vital to take all practicable steps to ensure workers are safe at work by eliminating, isolating or minimising the dust — and try to prevent it from becoming airborne in the first place.