Construction dust: Chasing concrete and raking mortar

Chasing concrete and raking mortar 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:

Assess

Identify and assess: Chasing concrete and raking mortar 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 grinder etc. will be particularly at risk. Follow the control steps below.

Control

Prevent: Think about limiting the risks before work starts by:

• limiting the need for chasing at the design/lay-out stage
• using a work method that limits/does not need chasing like over-covering cables

Control: Even if you minimise some of the dust this way, you may still need to do this work. Control the risk by:

• On-tool extraction – use a specially adapted grinder or chaser 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. For longer duration work (ie over an hour without a break) consider powered RPE with the same protection (eg TH2 powered hood/helmet). Fit testing is needed for tight fitting masks.

Review

• 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 the on-tool extraction system is correctly working on at least a weekly basis. Change filters as recommended by the supplier. Someone competent should examine any dust extraction equipment thoroughly and test its performance at least once every 14 months.
• 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

When uncontrolled both tasks quickly produce very high levels of silica containing dust. Watch the graph in the video clip below. 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 around 5 mg/m³.

Now watch the video below. The graph shows a dramatic drop in the amount of silica when using extraction. It is important to note that the extraction 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 extraction.