Practical filtration: Silica dust – much more than a nuisance

4 min read
An air cleaner and an industrial vacuum.
An air cleaner and an industrial vacuum.
An industrial vacuum controlling dust during pouring.
An industrial vacuum controlling dust during pouring.

Silica is a natural mineral present in large amounts in many solid 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. It is often then made airborne by simple tasks such as sweeping or pouring of powders and liquids. Regularly breathing in this dust can cause serious lung disease such as silicosis and lung cancer. In fact, silica is now the largest cause of occupational lung cancer after asbestos and construction workers and those working in the construction industry have 2-3 times greater risk of contracting COPD (Chronic obstructive pulmonary disease). It is a very serious issue and the statistics highlight the importance for contractors to capture dust at source and prevent dust getting airborne before it is too late. Dust has become far more than just a nuisance. It is life threatening and must be addressed. The National Federation of Roofing Contractors (NFRC) in the United Kingdom announced on 1st October 2012 that contractors will no longer have the option of using a cut-off saw to dry cut valley tiles. In order 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, James Miller believes that more needs to be done by everybody associated with the construction industries, especially those working indoors with power tools, to prevent the issue and to ensure other tradesmen in the same areas are left unaffected. Here are his top 10 tips for tackling silica in the workplace.

Identify the problem

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 that assessment by sampling the air that the workers breathe.

Look for replacements

One of the best ways to eliminate exposure is to use materials that do not contain crystalline silica. Adopting this approach completely eliminates any potential silica issues, and can create a completely safe, hazard free, working environment.

Use dust control products/systems

Use high efficiency cyclone-based mobile dust extractors or install temporary vacuum systems that are designed to work in the construction industry with suction guards fitted to power tools to capture dust at source and prevent dust getting airborne. In addition, always use HEPA-filtered construction vacuums in place of sweeping and use the vacuums to prevent dust getting airborne when pouring powders and liquids 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 to undertake these procedures are widely available for purchase or hire. Dustcontrol UK’s are all fitted with H13 HEPA filters and are built to Application Class H with reverse pulse filters on the vacuums to tackle dust on-site. These filters remove 99.95% of all particles greater than 0.3 mircons from the air that pass through. This means that the exhaust air from these products is the cleanest it can be. The right vacuums and air cleaners will not only drastically reduce airborne dust, but will help power tools last longer and work better. Other trades will not be affected, which will make the whole site more efficient.

Wet drilling or sawing

As advocated by the UK’s NFRC, use wet drilling or sawing to control dust. In addition, remove dust and debris with a wet vacuum or hose it down, rather than dry sweeping. With wet concrete coring, stainless steel wet vacuums can be used to extract slurry from the coring unit. This separates out debris inside the vacuum and simultaneously pumps away the cleaned water back to a drain or suitable collecting tank.

Monitoring

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

Think hygiene

An obvious one really, but 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.

Training

Make sure workers know about silicosis, silica-dust hazards and how to control their exposure. 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 crystalline silica dust. • How to handle, label, and store hazardous materials safely. • How to use and care for personal protective equipment. • How to use dust control equipment effectively.

Wear a mask

FFP3 dust masks will soon become a minimum standard in the United Kingdom, plus proper face fit tests will be required. Make sure all workers wear protective masks, and that they are fitted correctly.

Communication

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

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.   

How an extraction system works
An extraction system should always be equipped with a filter unit. The filter unit separates coarse material in the cyclone body of the unit and fine dust in an internal arrangement of conical pleated cartridge filters. Pleated filters have very high filter areas in relation to their physical size. The filter units therefore have high capacity while maintaining compact overall dimensions.Filters are cleaned with reverse pulse which results in very effective cleaning, long filter life and low maintenance.Normally the filter units are equipped with a plastic sack for collection of the extracted material but other types of discharge arrangements can also be installed. In the filter unit, dust is separated from the air in several steps – the cyclone will separate particles down to a size of 1/100 mm – the filter will separate particles which go through the cyclone. The dust laden air is introduced into the cyclone at a high velocity. Through centrifugal force the dust particles, with higher relative mass than the air molecules, are forced outward toward the wall of the cyclone and fall toward the bottom. The air flows toward the centre of the cyclone and through the filter. Permissible air-flow determines the air velocity through the filter material, known as filter loading. Consider also inlet/outlet velocities. Permissible filter loading varies with dust type.