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Silica dust: threat and mitigation

27 November 2012

Dust as an explosive hazard is a well-covered issue in Ex safety literature, but it also has non-explosive safety implications that can be just as dangerous over the long term. James Miller, managing director at dust extraction specialist Dustcontrol UK, looks at the threat of silica particles within dusty environments and suggests measures to protect personnel from this particular threat.

Silica is a natural mineral present in large amounts in many construction materials. The silica is broken into very fine dust (respirable crystalline silica or RCS) during common tasks such as cutting or grinding concrete, chasing out mortar or drilling in enclosed spaces, and can become airborne by simple tasks like sweeping or pouring of powders. Regularly breathing in this dust can cause serious lung disease such as silicosis or lung cancer. 

In fact, silica is now the largest cause of occupational lung cancer after asbestos, and construction workers have a serious risk of contracting COPD (Chronic obstructive pulmonary disease). There are estimated to be over 500 silica-related deaths per year in the UK.

The National Federation of Roofing Contractors (NFRC) is leading the way, having announced on the 1st October 2012 that contractors will no longer have the option of using a cut-off saw to dry cut valley tiles. To reduce risks from silica dust the industry is specifying that water suppression should be used where a cut-off saw is being used.

However, roofing is a small part of the construction industry, and more needs to be done by everybody working in any environment where silica dust might be present, particularly managers and foremen, as well as safety, health and hazardous area professionals.

When tackling silica, these steps should be taken:

1. Identify
Firstly, make a list of the activities that put workers at risk. For this it might be useful to bring in an industrial hygienist who can help make an assessment by sampling the air that the workers breath.

2. Substitute
One of the best ways to eliminate exposure is to use materials that don’t contain crystalline silica. Adopting this approach completely eliminates any potential silica issue, and creates a completely safe, hazard free, working environment.

3. Use dust control products and systems
High-efficiency cyclone-based mobile dust extractors should be used, as well as temporary vacuum systems that are designed to work in the maintenance/manufacturing industry with suction guards fitted to power tools to capture dust at source and prevent dusts getting airborne.

Always use dust extraction vacuum systems in place of sweeping and use the vacs to prevent dust getting airborne when pouring powders into mixing vessels. Complement this approach with airborne dust cleaners to draw down remaining ambient dust, which can be created simply by people walking around.

Products fitted with H13 HEPA filters and built to Application Class H with reverse pulse filters, for example, can remove 99.95% of all particles greater than 0.3 microns from the air. The right vacuum systems and air cleaners will not only drastically reduce airborne dust, but power tools will last longer and work better and other trades will not be affected, making the whole site more efficient.

4. Wet is best 
As already mentioned, the NFRC is imposing water suppression for its accredited roofers when cutting tiles.  Other workers in environments where silica is potentially a problem should also use wet drilling or sawing to control dust. 

Also, remove dust and debris with a wet vacuum or hose it down, rather than dry sweeping. With wet concrete coring, stainless steel wet vacs can extract slurry from the coring unit, separate out debris inside the system and simultaneously pump away the cleaned water back to a drain or suitable collecting tank.

5. Monitor
Monitor the air. It is the most effective way to determine workers’ exposure to silica dust. Air monitoring results can also help you decide the most appropriate methods for controlling crystalline silica dust. It’s important also to monitor the health of workers who may be exposed to crystalline silica dust. Workers should have regular medical exams: at a minimum before they begin their job and every 2-3 years after that.

6. Think hygiene
Those who work with materials containing crystalline silica should wash their hands before eating, drinking, or smoking. They should shower (if possible), and change into clean clothes before leaving the worksite. Facilities should be provided.

7. Training
Make sure workers know about silicosis, silica-dust hazards, and how to control their exposure. Their training should cover the following:
* The health effects of exposure to crystalline silica
* The importance of effective controls, safe work practices, and personal hygiene
* The purpose of boundaries or signs that identify work areas containing silica dust
* How to safely handle, label, and store hazardous materials
* How to use and care for personal protective equipment
* How to use dust control equipment effectively 

8. Wear a mask 
FFP3 dust masks will soon become a minimum standard, and proper face fit tests will be required. Make sure all workers wear protective masks, and that they are fitted correctly.

9. Communicate
Make sure any product that contains silica has a label that says so. Safety Data Sheets must also accompany products that contain more than 0.1% crystalline silica.

10. Warning Signs
Make sure signs are put up in the relevant spaces that identify work areas, tasks, and equipment that may expose workers to crystalline silica. The signs should warn workers about silica hazards and identify required personal protective equipment.

For more information go to: www.hse.gov.uk/pubns/cis36.pdf




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