Construction dust: Cutting paving blocks kerbs and flags
Using cut-off saws on paving, blocks and kerbs can produce very high levels of silica containing dust. Effective control is necessary because this work is high risk. This page tells you how to control the risk and why. You also need to be aware of the general information on construction dust.
What you must do
Follow the Assess, Control and Review model. Pay particular attention to the following things:
Identify and assess: Using cut-off saws on paving, blocks or kerbs can produce very high levels of silica containing dust. Anyone breathing in this dust cloud will be affected. Those using or very close to the cut-off saw will be particularly at risk. Follow the control steps below.
Prevent: Think about limiting the risks before work starts by:
- using lower energy equipment like a block splitter
- limiting the number of cuts during design / lay-out
- getting material cut off-site and delivered
Control: Even if you minimise some of the dust this way, you may still need to use a cut-off saw. Control the risk by:
- Water – use a hand-held cut-off saw with a water suppression attachment. Connect this to a supply of pressurised water container. Use water resistant markers if needed.
- On-tool extraction – use a specially adapted equipment with on-tool extraction. Select an H or M class extraction unit. Make sure the extraction flow rate is right for the work. Hose connections should be tight fitting and secure without obvious leaks.
- Respiratory Protective Equipment (RPE) – you also need RPE with an assigned protection factor of 20 (eg FFP3 disposable mask or half mask with a P3 filter). Make sure it is compatible with other items of personal protective equipment being worn. Fit testing is needed for tight fitting masks.
You will find more information on controlling the dust risks from this work below:
- Supervise: Ensure controls are properly used and RPE is worn correctly. Anyone using tight fitting masks also needs to be clean-shaven and face-fit tested.
- Maintain: Check water jets on the saw are clean, water containers well maintained and that any extraction equipment is clear of blockages Replace seals and worn cutting discs when needed. Properly store, and maintain non-disposable RPE. Change filters as recommended by the supplier.
- Monitor: You may need a health surveillance programme unless you are sure exposure to silica dust is well below the recommended exposure limit.
What you should know
This work often involves a number of quick cuts done throughout the day. That does not mean it is low risk. Uncontrolled cutting quickly produces very high levels of silica containing dust. Watch the graph in the video clip below. This shows how much silica is created when dry cutting. The Workplace Exposure Limit for silica is 0.1 mg/m3 when averaged over 8 hours. The work quickly produces very high peak exposures of up to 70 mg/m3.
Now watch the video below. The graph shows a dramatic drop in the amount of silica when using water suppression. It is important to note that the water does not capture all of the silica. RPE is also needed as a back up measure. It protects against this remaining level of unknown and variable silica risk. It also protects against high exposures caused accidentally by the worker or a fault with the water suppression.