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Dust – what is it good for? Issues with CFRP

If you are working in the composites industry and you haven’t risk assessed the impact of dust in your workplace then you could be putting your employees as well as your business at risk.


sanding

Let’s take carbon fibre reinforced plastics (CFRP) as an example. From fibre production through to trimming, moulding and finishing there are numerous activities that create dust. Whilst there is currently no CFRP specific guidance provided by the HSE any activity that creates dust above Workplace Exposure Limits (WELs) is potentially hazardous and falls under the legislation.

How much is too much?
So what are the potentially hazardous levels of dust in the workplace that you need to consider if working with CFRP? Well for starters, any dust in excessive amounts can cause respiratory problems. The HSE guidance suggests the following:

“any dust when present in the workplace at a concentration in air equal to or greater than 10 mg/m3 of inhalable dust or 4 mg/m3 of respirable dust (as a time-weighted average over an 8-hour period) is considered to be a substance hazardous to health”

What are the sources?
CFRP related dust can come from the gradual breakdown or abrasion of the fibres themselves, from the resin systems and also from fibre sizing compounds.

  • Carbon fibre is a ceramic mineral that is both hard and abrasive. The body cannot break down mineral materials so fibre fragments can get lodged in the lungs and cause long-term irritation and damage.
  • Dust, if sufficiently fine and in significant enough quantities (whether from CF or resins) can cause permanent lung damage.
  • CF dust entering the eyes can be an irritant due to its abrasive qualities.
  • Some fibre sizing agents are irritants and skin contact can be uncomfortable or cause longer-term issues such as dermatitis.

Carbon fibre dust also presents the user with two other non-health based issues. Firstly carbon fibre is conductive so any build-up of dust can lead to the shorting of electrical equipment. Secondly, its hard / abrasive qualities can also lead to accelerated wear on moving mechanical parts exposed to dust.

This presents a host of health-related and economic reasons why dust management is something all CFRP-based businesses must consider.

Is all dust the same?
In short, no! The reason for the different WELs on dust types is due to the size of the particles and thus how likely they are to get deep into the lungs.

  • Airborne dust is suspended in air, usually over 10 microns which the body can self-manage in limited concentrations.
  • Inhalable dust is between 2.5 and 10 microns, visible and can get trapped in the nose, mouth throat and upper respiratory tract where it can cause damage.
  • Respirable dust is less than 2.5 microns, invisible and can travel deeply into lungs where it can cause the most harm.

Causes of dust
The cutting and trimming of raw carbon fibre generate fragments which can also break down into dust. Grinding, trimming or shaping components is a major dust generator and has the added disadvantage of spreading the dust over significant distances when using powered tools. For example, a 50mm die grinder working at 20,000 rpm throws off dust at 52m/s! Surface sanding to promote the bonding of coatings and adhesives, whether by hand or by powered disk, can generate a significant amount of airborne dust.

carbon fibre cuttingPrevention and reduction before protection
The first step is to identify the source of the dust. Any uncontrolled work activity that generates dust, particularly in an enclosed environment is likely to create a dust problem. Any visible build-up of dust on windows, floors and benchtops should be investigated as this indicates a dust creation process that isn’t being well contained. If you suffer from a lot of electrical equipment shorts (computers, vacuum cleaners etc.) then this is also a good indicator of CFRP-based dust not being controlled.

Where dust is identified as an issue, control measures should be adopted and there are a number of factors to consider:

  • Work area(s) and local ventilation
  • Potential dispersion of the contamination
  • Who is potentially exposed to the dust

Initially, you should be looking to reduce dust production at source – the old adage of prevention rather than cure. This could be done by using thinner cutting tools or wet sanding rather than dry sanding. Secondly, ensure that you contain the remaining dust into managed areas by setting up air management / extraction systems that contain dust and remove it.

What is important here is that your dust / air management is fit for purpose. One size does not fit all and there are a wide variety of ways to do this from on-tool extraction through to centralised vacuum systems. All come with pros and cons; some can be low cost and some very expensive.

Once you have worked through prevention and reduction you then need to manage what’s left. This task usually falls to Personal Protection Equipment (PPE). When you have effectively reduced and contained dust the remainder is much simpler to deal with and the amounts of PPE required are often much less. Relying too heavily on PPE over other methods often carries this disadvantage of exposing more people to dust than you expect as airborne dust can easily travel into other production areas or offices.

Can I find out more?
The issues of dust in the composites industry have been getting a lot more attention recently. Indeed only this summer Composites UK ran a number of awareness courses with Dark Matter Composites (DMC). These are both excellent sources of advice if you have dust and want to know how to effectively manage it. The E-Book from the HSE is also a good place to start.

There is, however, one process where you can prevent dust production – surface preparation for painting, coating and bonding. If you want to know how to do that then contact us at Oxford Advanced Surfaces where we can improve productivity, reduce waste and eliminate dust all in one go!

Dust. What is it good for? Absolutely nothing!

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