There are several factors to consider when assessing the personal protective equipment (PPE) requirements of your workforce. Noise, temperature and visibility are all factors likely to impact the final decision as to which PPE is right for your workers – but a further key risk to consider is the build-up of static electricity.
Simple actions such as walking across workspace floors, dragging tools and equipment across non-conductive surfaces, and standing rather than sitting in work areas, can all increase static build-up. This can, however, be reduced and controlled with garments with anti-static properties.
The objective of anti-static properties in protective clothing is to reduce the fabric’s surface resistance (or alternative, increasing conductivity, the other side of the same coin) so that any charge can immediately dissipate across its surface and go to earth. If it cannot, then a charge may build to a point where it could jump to another, oppositely charged surface, creating a spark – which in the presence of explosive atmospheres or flammable fumes and liquids, could be highly dangerous. Even in areas where a potentially explosive atmosphere is not an issue, the presence of sensitive electronic equipment of components could be critically damaged by a discharge of static electricity; this is not just a safety issue. It can be about protecting valuable equipment and product.
There are two types of anti-static clothing: anti-static clothing made of woven materials and clothing to which an anti-static agent has been applied.
Woven anti-static clothing
Anti-static clothing made of woven materials, such as flame retardant (FR) clothing, generally achieve anti-static properties by including a conductive (usually carbon) thread in the weave. This thread is normally seen in the form of a dark coloured grid – and as carbon is conductive, it allows static charges to dissipate and go to earth harmlessly. The anti-static properties for this type of clothing will last the lifetime of the garment.
Clothing with anti-static coating
The alternative is clothing that has undergone surface treatment – usually through the application of an anti-static agent – to achieve anti-static properties. The treatment works by attracting/absorbing moisture from the air to create a thin moisture film on the surface of the fabric. Because moisture is conductive, it will enable a charge to dissipate across the surface of the clothing and go to earth harmlessly. Anti-static properties for this type of clothing, however, are short term and how effective they are and how long they last depends on a number of factors, including usage and the environment.
Factors that the affect anti-static properties of garments
In such garments the level of moisture in the atmosphere influences the surface conductivity capability of garments that have undergone surface treatment. Anti-static garments of this type, as mentioned previously, are reliant on absorbing moisture from the atmosphere to create a conductive film to dissipate an electrical charge. However, the surface treatment can fade – and in unusually dry environments the effectiveness of the garment’s anti-static properties will be reduced.
How can safety managers manage the risks and ensure anti-static garments work effectively?
- Ensure garments are always earthed
Without a route to earth, static charges may jump from the garment to conductive surfaces/materials in the vicinity, potentially damaging equipment or igniting a flammable atmosphere. With this considered, and regardless of how effective the surface treatment is, wearers of anti-static PPE must consider how static charges go to earth.
There are three ways to transfer static charges to earth:
- Through the human body
One of the best ways to dissipate static charges to earth is through the human body (we are mostly made of water), but this relies on constant contact between the wearer’s skin and the garment and assumes that the wearer’s footwear and the floor are conductive
- Through garments with attached socks to ensure constant contact with the floor
Another way of dissipating static charges harmlessly to earth is through anti-static garments with attached socks/booties that are worn over the wearer’s normal footwear, ensuring the fabric is in constant contact with the floor. (This of course assumes the floor is conductive and not insulated. If the charge cannot go to earth through the floor this will evidently not work).
- Through a conducting cable clipped to the anti-static clothing and to a known grounding point
Finally, a conducting cable – one end clipped to the anti-static clothing and another to a known grounding point – can transfer static charges to earth harmlessly
However, even with the above routes accounted for, it’s crucial that the earthed surface has a low surface resistance to allow electric charges to dissipate.
- Control the humidity of the environment
The EN test for surface resistance (EN 1149-1) is conducted in a relative humidity of 25%, which is very low – specifically to make the challenge greater for the surface treatment because less moisture is available to create the conductive film. In real world environments the humidity in most cases will be much higher than this so the anti-static treatment more effective (i.e. the surface resistance lower) than indicated by the test. However, in extreme cases where anti-static is critical, or where a dry atmosphere is common it may be important to monitor, or even where possible, control humidity to maximise the effectiveness of the treatment.”
- Limit usage, don’t re-use garments and check them regularly
Continued use of anti-static garments – particularly in environments where abrasion is a key concern – will degrade anti-static functionality and a damaged suit will not protect the wearer. If anti-static garments are used for extended periods of time, changing to new garments regularly is advised as any surface treatment will fade or rub off. Suits should not be re-used and washing or decontamination will remove anti-static treatment.
Ideally, safety managers should conduct routine checks of anti-static equipment and the environment to ensure anti-static garments are in optimal condition and the environment has enough moisture to promote effective protection.
Finally, in higher risk areas, i.e. explosive atmospheres, anti-static properties will be much more important as static discharge as a charge jumps from the garment to another surface can cause ignition. ATEX regulations do not relate to protective clothing or PPE other than recommending clothing certified to the EN 1149 anti-static standard (in fact, ATEX regulations are designed for equipment such as switches and tools and specifically exclude certification of workwear) . But this might not be enough; further reduction of the probability that clothing could create a static spark by more effective management of the use of that clothing should be a key consideration.
In the final analysis, in high-risk areas garments relying on a surface treatment for anti-static properties may not be enough and users should perhaps consider specialist garments that feature intrinsic anti-static properties – such as Lakeland’s “Pyrolon” range of disposable clothing which also combine flame retardency and chemical protection.
Ultimately, by following the points outlined in this blog, safety managers will be able to develop a more effective approach to the provisioning of anti-static PPE and ensure they provide the right protection for both the worker and the workplace.
By wearing the right chemical suit for your workplace, you can ensure a maximum level of safety with chemical hazards. Read our eBook for more clarity on this subject: