Sometimes when I machine cast iron the next day I have an upset stomach, this made me wonder whether cast iron dust is a health issue and I should be wearing a mask.
Machining Cast Iron
I machine cast iron without any cutting fluid and use tungsten carbide tools with a shallow angle. The result is the cast iron gets removed as quite small particles.
For a finishing cut I will take a very shallow cut and then repeat the cut at the same setting, again this tends to generate a lot of dust.
You can tell the dust can be very fine as it makes your hands go dark grey with handling and looks very similar to having handled graphite.
Is it doing me any harm?
Dust Removal
After a stint of machining I switch the Microclene filter on a leave the workshop to make a cup of tea. This small filter unit cleans down to roughly 5μm and will filter all of the air in my workshop roughly every 5 minutes.
There are a number of references around the different health and safety organisations listing the issues with cast iron dust. I’ve tried to group these below:
Breathing the Dust
Cast iron dust inhalation: Cast Iron dust is not the worst thing to breath into your lungs, also model makers tend to only work with cast iron occasionally and only short durations. However, you still need to be careful.
Not all inhaled particles produce scar tissue. Dusts such as carbon and iron remain within macrophages until they die normally. The released particles are then taken in again by other macrophages. If the amount of dust overwhelms the macrophages, dust particles coat the inner walls of the airways without causing scarring, but only producing mild damage, or maybe none at all.
https://www.ccohs.ca/oshanswers/chemicals/lungs_dust.html
Exposure to iron oxide, a substance sometimes encountered in cast iron grinding, is a danger, as well. This substance has been associated with cases of pulmonary siderosis, an occupational lung disease.
https://www.robovent.com/dust-collection/cast-iron-grinding-dust/
The simple solution is to wear a mask and to run an air filtration system in the workshop.
Combustion Risk
I had never heard of cast iron dust combustion until I saw this article:
Cast iron grinding facilities must be aware of dust accumulating in a confined space. These particulates, combined in just the right proportion with oxygen in such a space, pose an ignition risk. Dust explosions can be highly destructive and can cause injury or death to workers.
https://www.robovent.com/dust-collection/cast-iron-grinding-dust/
In most hobby workshops we won’t be making that much dust, any easy solution is to open the windows and get some air flowing through.
Ingestion of Iron
Cast iron dust ingestion is what has worried me for some time as I often get a bad stomach after machining cast iron.
Ingestion of less than 20 mg/kg of elemental iron is non-toxic. Ingestion of 20 mg/kg to 60 mg/kg results in moderate symptoms. Ingestion of more than 60 mg/kg can result in severe toxicity and lead to severe morbidity and mortality.
https://www.ncbi.nlm.nih.gov/books/NBK459224/
Conclusions
You do have to be careful both from an inhalation and ingestion viewpoint, but this is not the most dangerous of dusts in the workshop and hence:
- Cast Iron dust is not the worst thing to breath into your lungs, also model makers tend to only work with cast iron occasionally and only short durations.
- However, you still need to be careful.
- Wear a mask
- Open windows
- Use an air filter
- Wash hands
- Clean your clothes