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Are you wasting money AND exposing your employees?

23 October 2020

Fiona McGarry H M Inspector of Health and Safety and Health and Safety Executive lead for engineering and metalworking fluids looks at the issues surrounding the common practice of 'blowing down' metalworking fluids

Simulation of an operator using a compressed airline to remove MWF from a machined component, resulting in personal contamination with MWF droplets. The MWF was dosed with a blue dye, which under an ultra-violet lamp shows up as blue deposits on, left, the end of the arm and upper leg, and right, the upper torso and face

Metalworking fluid (MWF), often referred to as coolant or suds, is used during the machining of metals to provide lubrication and cooling. Compressed air guns (blowguns) are commonly used in the engineering industry for ‘blowing down’ to clean and remove MWF from machined parts and the bed of the machine. This blowing down creates mist/aerosol which can be breathed in by operators and others working in the vicinity.

Inhalation of MWF mist can cause serious lung disease, including occupational asthma and occupational hypersensitivity pneumonitis. The prosecution of a company after three workers developed debilitating lung conditions is a stark reminder of the need to control the risk. One worker has been so severely affected they have become virtually paralysed, another will never be able to work with MWF again, and a third must have special measures in place to ensure he never comes into contact with MWF. 

MWFs can cause dermatitis through direct contact with unprotected skin, particularly on the hands and forearms, or when MWF contaminates clothing and soaks through. Metalworking machine operatives are in the top five occupations with the highest annual rates of occupational dermatitis. Using compressed air for blowing down, increases the risk of inhaling MWF mist and causes splash contamination of skin and clothing, as can be seen in the photographs. 

The use of compressed air for blowing down also creates a number of safety hazards for those involved. Noise levels are normally high and there is a significant risk of permanent hearing damage from prolonged exposure. There is a risk of compressed air entering the operator's bloodstream, which can result in death. Eye injury including blindness can occur if dust particles or swarf bounce back at the operator.

You should look first to prevent exposure at source, so instead of blowing down components using compressed air guns, you should consider using alternatives. Examples include vacuum guns, absorbent materials, low-pressure coolant guns, spindle-mounted fans or automatic compressed air hoses (operated with computer numerically controlled (CNC) machine enclosure doors shut). Finished components can be cleaned in industrial washing/degreasing machines. The cleaning of machine surfaces using compressed air should be avoided, suitable swarf vacuums should be used to remove wet swarf and chips from machine surfaces.

Reduce exposure

However, where there is no practical alternative to using compressed air guns there are still measures you can take to reduce exposure. You should reduce the exit pressure of the compressed air to as low a level as practicable (as a guide 30psi/2.1bar is effective at cleaning). Different nozzle designs will also allow guns to be operated at a lower pressure and reduce noise levels. 

In addition, you should blow down components inside the CNC machine enclosure with the local exhaust ventilation running or provide a separate enclosure for cleaning purposes. You should also consider using compressed air guns with longer lances (e.g. 30 cm) as this increases the distance from the source of mist and reduces splashing on to the skin.

According to the British Compressed Air Society reducing the operating pressure of blowguns down to 2 bar, from the fixed system pressure of around 7 bar, can reduce operating costs by up to 60%. They suggest you check the operating pressure on all blowguns and discuss with the blowgun manufacturer whether it can operate at a reduced pressure. The pressure can be reduced by fitting pre-set tamper-proof regulators at the take off point from the fixed pipe system. It may be worth considering a separate pressure reduced supply for all blowguns.

Further information  
https://www.hse.gov.uk/engineering/faqs.htm   
https://www.hse.gov.uk/metalworking/index.htm   
https://www.bcas.org.uk/media/Download.aspx?MediaId=67  

 
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