I took this picture recently of a cupola furnace at a small foundry in Wigan. Scrap metal and coal are loaded into the top of the furnace and the coal set alight to melt the scrap and produce molten metal which is used to manufacture iron castings.
As there is insufficient oxygen for complete combustion, carbon monoxide is generated. Hydrogen sulphide can also be produced due to the presence of sulphur in the coal. Both of these gases are highly toxic and have to be extracted to minimise the risk to the operators. Some of the gases dissolve in the molten metal and can gas off as it cools, so there can be some risk during the casting operation itself.
This is a good example of how hazardous substances can be generated during a process and which are often forgotten by inexperienced or untrained people carrying out health risk assessments.
A number of years ago I got involved with a company (NOT the one shown in the picture, I should point out) where a worker had been exposed to high concentrations of carbon monoxide when inspecting the furnace when a leak occurred. The company concerned had employed a safety consultant to carry out COSHH assessments for them. Unfortunately he based his assessments on the material data sheets for the substances bought by the company. There were no data sheets for carbon monoxide or hydrogen sulphide as they aren’t bought in so there was no mention of two of the most serious risks in he foundry – i.e. potential exposure to the gases. There were other hazards he didn’t consider too – metal fume created during melting and casting and exposure to respirable crystalline silica during “fettling” (the grinding of the finished castings to remove rough edges) – because again, these substances are created by the process and are not bought in.
Although most people seem to think that COSHH requires an assessment to be carried out for substances, this isn’t actually the case – the assessment should actually cover the “risks created by work” where workers can be exposed to hazardous substances. It’s best to start by considering the process and what workers and others can be exposed to – both bought in substances and any that can be generated by the process itself. Quite often it is the latter that present the most significant risks, as is the case with the cupola furnace and other foundry operations. Listing the substances bought in and using the supplier’s data sheets as the basis of the assessment is likely to lead to significant risks being missed.
Note: COSHH is an acronym for the British Control of Substances Hazardous to Health Regulations 2002