Silica dust

This talk is about dust from cutting, drilling, grinding, or polishing materials that contain silica. Bricks, tiles, concrete, and mortar contain it. Sandstone contains more than 70 percent silica. Granite might contain 15 to 30 percent. Those figures are HSE's. The fine dust is respirable crystalline silica, RCS. It is too fine to see in normal lighting. If the air looks clear, that is not proof it is safe.

HSE says silica is the biggest risk to construction workers after asbestos. Heavy and prolonged exposure to RCS can cause lung cancer and other serious lung diseases. Silicosis can cause severe breathing problems and increases the risk of lung infections. It usually follows exposure over many years, but extremely high exposures can cause acute silicosis more quickly. HSE also links silica to chronic obstructive pulmonary disease, including bronchitis and emphysema. HSE commissioned estimates that silica dust was responsible for the death of over 500 construction workers in 2005. That figure is for 2005. It is not a count I have updated, and it is not a reason to treat today's cut as harmless.

The Control of Substances Hazardous to Health Regulations, COSHH, say you must protect against the risks from hazardous construction dust. HSE's leaflet for employees, INDG463, says control measures for RCS must be effective in keeping exposure below the workplace exposure limit of 0.1 milligrams per cubic metre of respirable dust, averaged over 8 hours. That is a limit for the controls to meet. It is not a target to work up to, and it is not something you can judge by eye.

Stop the dust getting into the air. HSE's construction dust sheet, CIS36, gives two main ways. Water damps the cloud down, but only if enough water is supplied at the right levels for the whole time the work is being done. Just wetting the material beforehand does not work. On-tool extraction removes dust as it is produced. It is local exhaust ventilation fitted to the tool: the tool, a capturing hood, an extraction unit, and tubing. Use an extraction unit to the correct specification. Do not just use a general commercial vacuum.

For silica, choose an H class or M class extraction unit. HSE's sheet on on-tool extraction, CIS69, says those units provide effective and reliable extraction and are fitted with low-flow indicators. Do not put a HEPA filter in a general commercial vacuum and call it done. An L class unit is only suitable for lower-toxicity dusts such as gypsum in plasterboard. It is not the unit for silica. The hood has to sit as close as possible to the work. Dust escapes through any gap. Empty the unit into the correct disposable waste bags, seal them, and put them in the right waste container. Do not empty the bags to recycle them. If you hire the unit, check with the hire company what examination they have done.

Water or extraction may not be enough. Often RPE has to be provided as well. HSE says the general level for construction dust is an assigned protection factor, APF, of 20. That means the wearer breathes one twentieth of the dust in the air. Common types at APF 20 are an FFP3 disposable mask, or a half mask with a P3 filter. For longer work, powered RPE such as a TH2 powered hood. CIS36 says consider powered RPE when people are working for more than an hour without a break, because disposable masks and half masks get uncomfortable. RPE is the last line of protection. If you are relying on RPE alone, HSE says you need to be able to justify why. Tight-fitting masks need a face-fit test, and the wearer needs to be clean shaven. The mask has to be the one that fits that person, not the one left on the dashboard.

For regular removal of dust and debris, CIS36 says damp it, or use vacuum attachments on an H or M class unit, and RPE with an APF of 20 depending on the location, the duration, and the dust. A brush, shovel, and bucket, after damping down, is described for minor one-off amounts, not as the everyday clean. Keep other people out of the dusty area. If the work still looks dusty, the control is not doing its job. Stop and tell the person in charge. Do not carry on and hope the mask will cover it.

On-tool extraction needs a thorough examination and test at least every 14 months, by someone with the right knowledge, and a record that it was done. CIS69 also says formal maintenance checks at least once a week, and more often if the kit is getting damaged. A blocked filter is not a small annoyance. It is the control switched off.