Footwear for Chemical Protection
Published: 10th Jan 2011
SATRA’s Peter Doughty highlights some key requirements and latest developments for chemical protection footwear intended for supply into the EU.
Along with the many advances in medical research has come a greater understanding of the way our bodies work and how they react when exposed to the ever-increasing number of highly concentrated and dangerous chemicals associated with the modern world.
When combined with the almost daily announcements about potential health effects caused by long or short term exposure to chemicals that were once considered to be safe, it becomes apparent just how important it is to minimise our contact with any substance that may have an adverse reaction to human health.
In terms of splashes and spills from liquid chemicals in an industrial environment, a worker’s lower limbs and feet can be of particular concern and, therefore, specialist footwear has been developed to protect against exposure to chemicals.
The level of protection against chemicals provided by any particular item of footwear will depend not only on the construction of the boot in terms of its height and freedom from holes, but also the choice of materials used to produce the footwear, as it needs to be resistant to the chemicals against which protection is required.
The wearer’s foot is protected because the chemicals are prevented from reaching the inside of the footwear. To be effective, each material must not only resist the passage of the chemicals through its structure (termed ‘permeation’),?but must also resist degradation by the chemicals that would lead to damage - such as cracking or holing.
Chemical permeation is a process by which a chemical moves through a material at the molecular level, involving absorption of molecules of the chemical into the contacted (outside) surface of a material, diffusion of the absorbed molecules into the material and desorption of the molecule from the opposite (inside) surface of the material.
The permeation test involves exposing the outer surface of the sample to the test chemical in one section of a two-part cell, while circulating an inert gas or suitable liquid through the other part of the cell.
During the test, the amount of test chemical that permeates through to the inert collecting medium is measured until a predetermined permeation rate is reached.
The time for this to occur, known as the ‘breakthrough time’, is recorded and determines the material’s performance level.
EN 13832-3 currently includes five performance levels for permeation resistance. At performance level 1, permeation breakthrough occurs between 121 and 240 minutes. At level 2, breakthrough is between 241 and 480 minutes, at level 3 it occurs between 481 and 1,440 minutes and at level 4, permeation breakthrough happens between 1,441 and 1,920 minutes. At level 5, breakthrough occurs at any time after 1,921 minutes.
Generally, it is relatively simple to assess the resistance of a footwear material to permeation or degradation by a specific chemical. However, the value of the information gained from testing with only one chemical is limited. It may provide some indication of the possible behaviour with a similar chemical, but will reveal nothing about the material’s resistance to permeation or degradation by a quite different type of chemical. For this reason, it is important to ensure that materials are chosen on the basis of known resistance to the particular chemicals against which the footwear is intended to protect, not simply on information about performance with other chemicals which may be of no relevance.
In Europe, products such as footwear providing protection against chemicals fall within the scope of EC Directive 89/686 - the Personal Protective Equipment (PPE) Directive - and must undergo the procedures within these regulations before they can be placed on the European market.
The Personal Protective Equipment (PPE) Directive 89/686/EEC is intended to ensure that PPE (any product designed to be worn or held by an individual for protection against one or more safety or health hazards) placed on the market in the EU, is fit for its intended purpose. Typical examples are safety footwear, protective gloves and eyewear. All items of PPE that come under the scope of the Directive and are placed on the market in an EU country after June 30, 1995 must be CE marked under the PPE Directive (89/686/EEC).
Before the CE mark can be affixed to the product, the manufacturer must follow certain procedures. Some of these involve the use of a third party organisation, known as a ‘Notified Body’.
Notified Bodies are EU-based organisations which, on the basis of their ability to carry out the examinations and tests required?for the CE marking of PPE, have been appointed by the government of that country and notified to the European Commission. SATRA is a Notified Body for most types of PPE.
Footwear providing protection against hazardous chemicals falls into the PPE Directive ‘complex design’ category. The design of the prototype and associated documentation must be certified by a Notified Body in accordance with Article 10 of Directive 89/686/EEC, and production is subject to ongoing conformity assessment under Article 11 of the Directive.
In 2006, CEN (the European standards-making body), published EN 13832 - ‘Footwear protecting against chemicals’, which gives details of the tests to be carried out on such footwear and the requirements to be met.
EN 13832:2006 consists of three parts. Part 1 covers terminology and provides details of specialised test procedures such as permeation and degradation.
Part 2 specifies requirements for ‘footwear resistant to chemicals’ and, by reference to the standards for safety and occupational footwear (namely EN ISO 20345-7), covers issues such as physical performance of the upper and outsole materials, and criteria for other protective features offered by the footwear - including protection to the toes against impact.
Part 3 similarly specifies requirements for ‘footwear highly resistant to chemicals’. It covers ‘all-rubber and all-polymeric footwear’ and specifically excludes leather footwear, low shoe and ankle boot designs. Part 2 allows greater flexibility to the footwear designer than part 3 by permitting the use of ankle boot styles and by not restricting the choice of material types other than by excluding leather outsoles.
Both parts 2 and 3 list the chemicals to be used in applying the standard and specify the marking to be applied to the footwear and the information to be supplied by the manufacturer. This includes details of the chemicals against which the footwear has been tested.
In terms of resistance of the footwear to chemicals, part 2 of the standard includes only the degradation testing procedure. Regarding the assessment of resistance to chemical penetration, the standard requires all-rubber and all-polymeric footwear constructions to pass the air leakproofness test, and other footwear to meet a dynamic wear trial type test for resistance to water penetration. However, it is important to realise that the fact that an item of footwear is airtight or performs well in a water penetration test does not mean that the footwear is capable of protecting wearers against chemicals. At best, it shows that the footwear may be able to do this. For these reasons, there have been requests at CEN Technical Committee level for part 2 of EN 13832 to be withdrawn as a harmonised standard because it does not adequately address protective properties.
Part 3 of EN 13832 covers the situations where a higher level of confidence in the protective properties of the footwear is required - for example, in higher-risk situations, such as when a particularly aggressive chemical is involved. Unlike part 2, part 3 requires both the footwear’s resistance to both chemical permeation and chemical degradation resistance to be tested, and includes the five performance levels based on the previously mentioned permeation test results.
As part of the ongoing review of published standards, it was agreed at the November 2008 meeting of CEN/TC161 (the committee responsible for drafting EN 13832) to start the process of revising part 3 of EN 13832. The public enquiry phase of part 3 was concluded during 2010 and these comments are currently being collated ready for consideration by the CEN Working Group.
However, more recently, a situation regarding permeation testing has arisen following various actions in France. The concern arose following a survey of French wine makers using chemical suits to protect against pesticides, which showed that concentration levels in many cases had been higher inside the suits than outside.
A subsequent market surveillance exercise had found that many chemical suit products of this type on the market failed to comply with the harmonised standard. Failures were found in permeation testing, user information and chemical degradation. The standard for these chemical suits currently allows permeation tests to be carried out using either the glove or clothing test procedure, which are different in terms of key test parameters.
The European Commission expressed concern that there were two different test procedures for the same property. However, there are in reality three procedures, as the footwear standard EN 13832 uses a third permeation test that is different again (in such aspects as temperature and flow rate). This means that a full suit, consisting of a garment, gloves and boots could be subject to three different permeation test procedures, namely EN 374-3 for the glove, EN ISO 6925 for the garment and EN 13832-3 for the footwear.
The main conclusion reached from this is that having three different test methods to measure the same property (potentially on the same material) is not a sensible solution, as differences in the methods can lead to different results. This causes additional complication for no apparent benefit and has now led to the formation of a European Technical Committee joint project group, with representatives from the clothing (TC162/WG3), gloves (TC162/WG8) and footwear (TC161/WG1) standards committees who will try to agree just one method for permeation. EN ISO 6529 (for chemical clothing) and EN 374-3 (for chemical gloves) are both currently under revision, and it has been proposed that they should be revised to use the same method.
Any agreed universal permeation test method is likely to be documented in a new European or international procedure that can be referenced from all the various product standards. This should help raw material suppliers, as there will only be one procedure, which will make it easier for end-users to directly compare the performance of different product types, thereby ensuring that the protective ensemble has consistent and appropriate levels of protection. These discussions will also provide an ideal opportunity to review parameters to be recorded during the permeation test.
At present, most standards use breakthrough time (as highlighted earlier) to classify performance, although this does not take into consideration the effects of gradual build up of permeated chemical. For instance, a material that constantly permits the chemical to permeate through its structure, but at a permeation rate just below that used to define breakthrough time would achieve a very high (good) result in terms of breakthrough time.
However, this could be potentially misleading for the user in terms of protection afforded, as during this time he or she could be exposed to significant levels of potentially dangerous chemicals.
The initiative to create a new unique universal permeation test procedure will mean that the revision of the various parts of EN 13832 will now have to be carried out to take this possibility into account.
Gaining PPE certification
Since the implementation of the PPE Directive in 1995, SATRA has become one of the leading Notified Bodies for certifying PPE intended for supply within Europe.
The organisation has also been influential in the development of related test methods and safety standards for many types of PPE, including footwear providing protection against chemicals.
In addition, SATRA has recently published a Slip Resistance Guide (which can be downloaded from www.satra.co.uk/slip_guide , giving a concise overview of slip resistance in relation to safety, occupational and protective footwear supplied into the European market.
SATRA has also developed an online guide to more general PPE testing (www.satrappeguide.com). Both of these initiatives aim to help product developers and buyers to better understand the legal and practices requirements.
Anyone interested in the testing or certification of footwear protecting against chemicals is invited to contact Martin Heels (firstname.lastname@example.org).
To contribute or comment on the future revision of EN 13832, email Peter Doughty (email@example.com).
Peter Doughty, Business Manager Protective Clothing and Safety Products.
Peter is responsible for all protective clothing (PPE) and safety products testing and CE marking and he sits on and chairs a number of standards technical committees and European working groups. He joined SATRA in 1986 and has been involved with research projects, test method development and for the last 15 years testing and certification of PPE. www.osedirectory.com/health-and-safety.php
Published: 10th Jan 2011 in Health and Safety International