Circular saw benches are widely used in woodworking industries.
The obvious risk of injury and precautions needed to control that risk
such as guarding and safe systems of work are well known.
Less well known are the risks to health from exposure to wood dust and how those risks can be controlled.
Here the operator is wearing special equipment which measures dust levels in his breathing zone
and allows them to be displayed as a graph on screen.
Without any effective extraction
very high levels of airborne wood dust can be produced, many times the UK exposure limit
which can cause a range of health problems including asthma and a rare form of nasal cancer.
Unfortunately for wood workers many of these airborne dust particles are virtually invisible under normal lighting conditions
so they may not be aware that they’re being exposed.
However by using a dust lamp you can make this normally invisible dust visible.
A dust lamp is a simple cheap readily available and powerful tool.
To use it you mount it on a stand such as a tripod
and point the lamp so that it shines through the dust cloud.
Walk around the process and look back towards the lamp
at a slight angle to the beam and the dust cloud will become visible.
You’ll see it better if you shield your eyes from the main beam using a book or board.
It’ll help if you lower the background lighting by turning off any workshop lights.
You could set up a black background behind the lamp which will make the dust cloud stand out even more.
You can make a record of your observations using a stills or video camera.
As before, the dust will be more visible if you block the main beam from shining into the lense
A saw blade acts as a crude fan that creates jets of dust laden air which produce the wood dust cloud.
Many saw tables have an extracted top guard covering the blade.
This acts as an enclosing hood which receives and controls the saw blade airflow.
Although extracted top guards will reduce the wood dust cloud,
some dusty air may still escape and cause exposure levels to go over the UK limit.
You can improve the effectiveness of the extracted top guard by increasing the flow rate.
This can be achieved by firstly using wider extraction ducting.
This may require an adaptor to connect to the guard
and secondly, keeping the length of flexible ducting as short as you can by using rigid ducting where possible.
In addition to the top guard its also important to have effective dust extraction connected to the underside of the saw bench.
A poorly designed and crudely fitted hood like this
may move a lot of air but not much wood dust.
A well designed replacement will give a significant reduction in dust levels.
Properly designed hoods for under the table are commercially available for most machines
or you can build your own effective enclosure like this one quite cheaply using plywood and rubber seals.
You need to make sure that the design allows air to enter so that the extraction is not starved of air which will stop it from working properly.
If your saw motor is positioned inside the hood
make sure that you have a continual flow of air to prevent a build up of dust
which may be a fire or explosion risk.
It’s a good idea to have an inspection hatch built into the extraction system
so that any scrap pieces that might cause blockages can be easily removed.
Making these changes will significantly improve your dust control.
You’ll also be using yourextraction system much more efficiently
so it will reduce your running costs.
On this machine for example it was found that after all of the improvements
the optimum flow rate was nine hundred and thirty cubic metres an hour
with a hundred and thirty cubic metres per hour at the top guard
and eight hundred cubic metres per hour at the under the table hood.
This gave average dust concentrations of less than half the exposure limit.
Over a hundred times better than cutting without any effective extraction.
However, it's important to note that each circular saw will require its own optimum flow rate to be determined.
Once the correct optimum airflow rates are known,
fitting and setting airflow indicators will maintain control .
and allow you to see at a glance if your LEV system is continuing to supply the correct airflow
In summary,
circular saw benches produce large airborne wood dust clouds that you may not be aware of or controlling effectively.
A dust lamp will help you see how and where the cloud escapes
and provide a visual check that your improved extraction is working.
Simple and low cost measures such as improving saw blade enclosures
and balancing extract airflows will provide improved control.
These simple techniques can be applied to most dusty woodworking processes.