Controlling silica exposure during fettling of castings

In foundries, once  the casting is removed from the mould it is usually necessary to remove excess metal and remedy defects. This process is usually referred to as “fettling” or “finishing”.

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Fettling normally involves the use of powered hand tools such as chippers and grinders. The operation presents a number of significant risks. Using power tools exposes the workers to high noise levels and hand-arm vibration. There is also a risk from exposure to the dust generated by the process. The dust will largely consist of metal particles, but this is usually of low toxicity. The main concern occurs where sand is used for the moulds in which the metal is cast. This is crystalline silica. Some particles of sand from the mould adhere to the metal and grinding during fettling can lead to the release of fine dust including particles of respirable crystalline silica. “Respirable”  particles are smaller than 10 microns in diameter and can reach the deepest regions of the lung. Regular, repeated exposure to respirable crystalline silica can lead to silicosis, a serious, debilitating lung disease.

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Risk of silicosis – Source: HSL

Respirable crystalline silica has a very low Workplace Exposure Limit of 0.1 mg/m3 as respirable dust. In fact, as the above chart shows, long term exposures to concentrations much lower than this can lead to some workers developing silicosis. There is also evidence that prolonged workplace exposure to crystalline silica can lead to an increased risk of lung cancer, although this is only likely to occur in those workers who have already developed silicosis. Given the nature of the risk exposures need to be reduced as low as practicable.

So, it’s important to ensure that the dust generated during fettling is properly controlled, particularly when there is a risk of exposure to silica. In most cases, the most practical and effective way of doing this is to install well designed local exhaust ventilation. The Health and Safety Executive have developed a number of sheets providing practical advice on how to control dust and fume generated during foundry processes, including fettling. For small castings they recommend the installation of an extracted booth. The work is carried out inside the booth which then contains the dust generated allowing it to be removed effectively by the extraction.

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Source: HSE COSHH Essentials for foundries. FD7 “Fettling small castings”

Recently, one of our consultants was carrying out a survey in a foundry. They had installed this type of booth for their fettling operations. However, as can be seen in the following photograph,  The booth was not being used in the way intended – the worker was carrying out the work outside the booth.

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The dust generated was not contained and, consequently, the extraction would not be as effective as it should be. The worker will have a higher exposure than if he carried out the fettling inside the booth.

In a previous post I outlined the key steps needed to control health hazards in the workplace. The first steps are recognising that a risk exists and then making sure that appropriate, effective controls are specified, designed and implemented. In this case the risk from dust exposure was recognised and a local exhaust ventilation system with an appropriate hood design was installed. The problem is that it is not being used properly, considerably reducing its effectiveness.

Once controls have been implemented they need to be properly managed to ensure that during use they continue to do the job they were designed to do. This requires training, supervision, maintenance, testing, audit and review. It’s a management responsibility to ensure that controls are properly used so more vigilant supervision seems to be required.

In this example, there could be a number of possible reasons why the booth was not being used correctly. Perhaps management and the workforce don’t fully understand the health risks and so don’t appreciate the importance of using the controls properly. Perhaps the workers haven’t been properly trained on how to use the booth. However, there could be a problem with the design of the booth. It is possible that carrying out the work inside the enclosure presents the operator with some practical difficulties. Perhaps the fine work required is difficult to complete properly if the casting is inside the booth or the booth dimensions, particularly the height, could cause the worker to adopt an awkward posture which causes discomfort and could lead to musculoskeletal problems. Solving one problem often creates another. Ergonomics is often neglected when designing engineering controls for chemical hazards. Ideally workers need to be consulted and involved in the specification and design of the controls and its good practice to build and test a prototype before finalising the design. Proper commissioning of the controls should also check for usability.

Further investigation would be required to get to the root cause of this problem. However, the case illustrates the importance of proper management of the design, implementation and use of controls.

About ms6282

I'm a consultant and trainer specialising in the recognition, evaluation and control of health hazards in the workplace. I'm based in the North West of England, but am willing to travel (almost) anywhere
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