uvex electrostatic discharge protective clothing

Electrostatic discharge capability of clothing – part one of two

This post is also available in: German

Electrostatic build-up and its uncontrolled discharge can have serious consequences for people – with both direct and indirect ramifications for the person affected. By way of example, we take the standards EN 1149 and EN 61340 and describe two scenarios which illustrate the difference between protective antistatic and ESD clothing.

 

Scenario 1: An employee working in the food industry triggers a flammable discharge during an apparently banal activity – this causes an explosion.

This happens because of friction created by the employee’s movements. Two bodies coming into contact – for example an upper arm rubbing against a torso as two people walk past each other – causes electrostatic build-up. If this dangerous energy were to suddenly be released, a mixture of dust and air or even of air and gas could be ignited and cause an explosion. In this instance, the direct victim would be the employee at work.

Scenario 2: An employee unwittingly transfers destructive energy to electronic components – once again, this arises from clothes rubbing together.

In the semiconductor manufacturing industry, a lot of work involves sensitive electrical components. While humans only perceive power surges from around 3,500 V, even low voltages of approximately 100 V can cause major damage to these components. The victim in this case is not directly the employee who causes the uncontrolled discharge. Rather, it is whoever is held responsible for an incorrectly functioning end device in case of doubt.

 

The difference between these two scenarios is clear: in the first example, the human trigger, that is to say whoever releases the charge, is directly exposed to the dangerous consequences of the uncontrolled electrostatic discharge. In the other, they are not. That and the very different energy values at play here ultimately demand two standards to counteract this danger and describe the respective requirements to this end.

 

EN 1149-5 – the antistatic standard

uvex en 1149In the first scenario, clothing must fulfil the requirements for the antistatic standard EN 1149-5. The person, i.e. the trigger, must be directly protected. The clothing used in this situation must therefore be personal protective equipment (PPE). Consequently, this clothing must comply with all general requirements for PPE (PPE regulation 2016/425 [formerly EC Directive 89/686/EEC]) – and especially the requirements for protective clothing in accordance with EN ISO 13688.

 

EN 61340-5-1 – the ESD standard

uvex ESD-SiegelIn the second scenario, it is not about protecting the person working on the product against potential harm, but rather the product itself. In terms of clothing, therefore, PPE is not required. Problematic voltages can, for example, be caused by friction, induction, corona or contact charging. The standard with which clothing must comply is EN 61340-5-1. While ESD (electrostatic discharge) clothing may not actually be PPE, it is subject to a raft of requirements: the clothing must prevent low-voltage electrostatic build up (from 100 V up) and discharge this in a controlled manner. This places complex material requirements on the clothing.

 

Here are the key facts once again at a glance:

ANTISTATIC (EN 1149-1; EN 1149-2; EN 1149-3; EN 1149-5) ESD EN 61340-5-1 (EN 61340-5-2)
Objective Prevent electrostatic build-up
Prevent explosive discharge
Prevent hazardous charge potential (voltage from 100 V)
Discharge electrostatic build-up in a risk-free manner
Area of application Environments in which there is an inherent risk of explosion, including the chemical industry, environments where the air contains gas (e.g. fuel depots, refineries) or dust (e.g. silos, conveyor units, mixing plants and mills) Working on and with sensitive components in the semiconductor, electronics, automotive and pharmaceutical industries.
Who is protected? The wearer – this clothing therefore counts as PPE too The object (e.g. an electronic component)
Protection against what energy level? Energy contents which can lead to explosive discharges Even low energy contents and voltages of
100 V an above (caused e.g. by friction,  induction, corona or contact charges)
The clothing
Categorised as PPE – it must comply with all general requirements for PPE (EC Directive 89/686/EEC) in addition to all requirements for protective clothing (EN ISO 13688). When not PPE – in addition to the requirements that all metal components are covered at all times, there are only recommendations regarding general requirements for clothing, e.g. high breathability.
  In addition to the relevant base material, all design, construction and manufacturing aspects as well as additional components must comply with requirements. Seams must not present any weak points, as the complete garment is checked. To reduce weak points, relevant static dissipative threads are often used.
  Metal components must always be covered.

Table 1: Comparison of the application areas of antistatic and ESD clothing

 

Relevant environmental factors

The basic requirement for unrestricted clothing function, irrespective of the applied standard, is that the wearer must be earthed. This applies to working environments in which antistatic protection is required, often via a suitable footwear-floor system. This footwear-floor system ensures that wearers are earthed and can also be used for standing and moving activities in an ESD environment. However, seated activities (additionally) require a wristband which ensures equipotential bonding despite minimal contact with the floor.

 

Moreover, there are two further factors which encourage electrostatic build-up and discharge: humidity and ambient temperature. Dry environments with humidity of around 20%, such as in the paper industry for example, cause far more build-up when two materials are rubbed together than would be the case in environments with a humidity level of 65%. It can therefore be said that the hazard posed by static build-up is much less pronounced in summer than in winter. However, where ESD is concerned, excess humidity can have a detrimental effect on soldering properties, meaning that corrosion damage can occur.

 

ANTISTATIC (EN 1149-1; EN 1149-2; EN 1149-3; EN 1149-5) ESD EN 61340-5-1 (EN 61340-5-2)
Points for consideration when wearing the clothing Clothing must always be worn in a combination of suitable jacket and overalls/trousers. It is the responsibility of the company to decide which areas of the body must be covered. Generally speaking, covering the upper body should be sufficient.
  The person in question must always be earthed, for example via a suitable footwear-floor system. The person in question must always be earthed, for example by wearing a wristband during seated activities and via a suitable footwear-floor system for activities carried out while standing.
  Clothing must always be done up when worn, totally covering any clothes worn underneath.
  Putting on and taking off the clothing is not permitted within the danger zone.

Table 2: Comparison of antistatic and ESD clothing

 

 

This truly is an “electrifying” topic in the truest sense of the word. We will continue this discussion in a second article soon. You will learn even more about the materials used, relevant standard checking criteria and uvex’s product portfolio.

 

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