Many of the test methods used in product standards for PPE need to be improved so that there is more consistency of test results between testing laboratories.
This article concentrates on work to improve the test methods in product standards for heat and flame protective apparel, reviews imminent changes to related product standards and lists new or recently published ones, some of which deal with PPE ensembles, not just apparel.
The standardisation activities covered in this article are those of ISO, the International Organisation for Standardisation, and of CEN, the Committee for European Normalisation.
Improving test methods
There is increasing realisation that the lack of adequate consistency (expressed as reproducibility) of test results from many test methods, such as those called up in product standards (that is performance specifications) for the heat and flame protective clothing sector, is causing problems for PPE end users. They may not be aware that if they permit test data to be provided by more than one testing laboratory, they may not obtain the correct technical ranking of competing items of PPE offered by responders to a tender.
For example, depending on the identity of the testing laboratories submitting test results, there could be at least a 10% difference in heat transfer values when testing to EN ISO 6942, the radiant heat exposure test called up in product standards such as EN ISO 11612 (for industrial fire protective clothing) and EN 469 (for clothing for fighting fires in structures). A Radiant Heat Transfer Index (RHTI) value of 20 seconds in one test laboratory might be 18 or even less in another, or 22 or more in another when testing the same sample of firefighter clothing material.
An interesting and encouraging observation is that for most test methods the consistency of results from repeat tests of different specimens of the same sample in one testing laboratory is usually excellent – see later for specific discussion on what is termed, not surprisingly, repeatability and also reproducibility.
“there is increasing realisation that the lack of adequate consistency of test results is causing problems for PPE end users”
Some tenders for PPE for firefighters stipulate that at least all key protective property tests are undertaken in one named testing laboratory to ensure a correct technical ranking is obtained. Examples have been tenders from Fire and Rescue Services in Australia and UK, stipulating a specific testing laboratory. This philosophy does not, of course necessarily mean that the test results from the chosen testing laboratory are numerically “correct” particularly if they result in one or more items of PPE offered by the bidders for the tender failing to meet the performance requirement set out in the tender documents – use of another test house could result in the same technical ranking of bidder’s items but with no samples failing a performance requirement. While we support tenders specifying a sole source for test data, we recognise that a preferred solution to the reproducibility problem is to improve test methods.
Working in a major testing and certification body operating worldwide, the problem of poor reproducibility between testing laboratories is very clear – we will see that our own test data is sometimes different from another testing laboratory, even when we are certain that the test samples are identical.
ISO and CEN standardisation committee members support ballots requesting revision of test methods when these come up for review every five years, the options being Confirm, Revise or Withdraw. We do this on the understanding that a key objective of a specific revision is to improve reproducibility of test results.
Test method revisions
The following is a detailed example of current and planned revisions of test methods in the heat and flame PPE sector.
Revision of EN ISO 6942 – “Protective clothing – Protection against heat and fire – Method of test: Evaluation of materials and material assemblies when exposed to a source of radiant heat”.
This test is specified in the industrial heat and flame sector and the firefighting sector of product standards – EN ISO 11612 (industrial), EN 407 (industrial -gloves), EN 469 (firefighting in structures), EN ISO 15384 (wildland firefighting), EN 13911 (firefighting – fire hoods), ISO 11999-3 (firefighting in structures) being some key examples.
Note that EN and EN ISO product standards will reference this test method as EN ISO 6942 but that ISO and, for example, Australian product standards, will reference ISO 6942. The key point is that regardless of the standards organisation referencing a test method if the numerical identity, in this case “6942” is quoted, then the test is identical.
This test method was originally developed in Germany and published as DIN 4842 in 1977. In 1993 it was slightly revised into a CEN standard as EN 366, then modified in 2003 to become the current standard and featuring an improved, more responsive heat sensor. When it came up for five yearly review a few years ago, BTTG, as part of the UK delegation to the ISO committee that is responsible for this test method, proposed its revision with a technical justification – not surprisingly the need for improved reproducibility. This justification was accepted by the committee and because BTTG has proposed revision, we were given responsibility for leading the work.
The process of revision, typical for all ISO or CEN revisions of test methods, is for a group of experts from testing laboratories who are members of the relevant committee to work together led by a named individual as project leader.
“an interlaboratory trial was organised involving 10 testing laboratories, to determine if testing consistency had been improved”
The first task here was for the project leader to draft proposed changes to the existing test method and get these provisionally agreed by the experts involved. An interlaboratory trial was then organised involving some 10 testing laboratories, the protocol being to undertake testing to the existing method and to the proposed revised method, so as to determine if the consistency (the reproducibility) of results between these participants had been improved. Several different materials have been included in these trials – fabrics in single layers as used in industrial coveralls, fabrics/ materials used as multilayers in clothing for fighting fires in structures or aluminium coated fabrics for high levels of protection against radiant heat.
The results are currently being analysed to determine if a reproducibility improvement has been achieved. The next step is likely to be for the committee to agree to any changes to the draft procedure used in these trials indicated as necessary to improve its content. Three stages of voting by the nations who are members of the committee are then expected to take place, two being to get technical comments which may lead to further changes to the draft, the final vote being essentially a “yes” or “no” as to whether a nation agrees to publication. In this case and typical of a revision process the time scale from agreed commencement of work is expected to be 36 months, extended to 48 if a voting stage leads to a need for it being repeated if there is a negative, that is a fail, outcome.
This particular revision is extremely important because 6942 is called up in many product standards for protective clothing including gloves and hoods – ISO, EN ISO, EN etc.
A very significant aspect of any test method revision, and one that at this stage cannot be ruled out with this example, is that if the comparison of results from the current test method and the proposed revised version show more than, on average, say a 10% increase or decrease which will lead to borderline products to a specific product standard’s performance requirements either passing with an increased margin or clearly failing. The standards committees responsible for specific product standards will then have to decide whether to adjust their pass/fail criteria.
When EN 366, mentioned above, was revised into the current EN ISO 6942, the change to the design and thus response of the calorimeter to the radiant heat challenge resulted in the need to change the performance requirements in EN 469:1995 into the current 2003 edition. This was to reduce the RHTI requirement from 22 seconds to 18 seconds, this being the average change that a testing laboratory would achieve if it tested a typical multilayer 469 assembly to the old and new test method. This apparent reduction in protection of firefighters – now 18 seconds until predicted onset of second degree burns compared to 22 seconds previously – was inevitably badly received by the firefighting community who needed to understand that no performance reduction had been introduced. It is to be hoped that this current revision does not lead to the need to revise any product performance requirement standards!
Expanding on the distinction mentioned above between Reproducibility and Repeatability, for all test methods in the textiles and related sector the test data for the latter is always the more consistent, sometimes by a very considerable margin. This suggests that either the test procedure – mounting/preparation of test specimens for example – or the specification of the testing apparatus is inadequate and/or ambiguous, leading to construction differences.
Revision of EN ISO 11092 – “textiles – physiological effects – measurement of thermal and water vapour resistance under steady state conditions (sweating guarded-hotplate test)
This test method, now in its second edition dated 2014, is called up in many protective clothing product standards as well as in other textile sectors such as bedding. Recently it has become very obvious that the consistency of results between testing laboratories is not acceptable. This is because it is leading to results from a laboratory meeting a product performance requirement in a standard but another laboratory giving a fail result. The firefighting sector want the lowest possible Water Vapour Resistance, that is the highest possible removal of perspiration, because it is essential that firefighters keep their body core temperature at a safe limit. Product standards express the result of this test as m2 .Pascal/Watt, the lower this value is, the better is the breathability of the combination of materials used to create the protective clothing. For example, the Australian product standard, AS 4967:2019, has reduced this numerical value from 25 to 20 compared to its previous edition.
Inter-laboratory trials involving more than 30 testing laboratories worldwide, plus additional test data generated by BTTG and compared to some other laboratories, reinforces the need for this revision. It is expected that work will commence in the relevant ISO textiles committee this year. Preliminary discussions between us and Hohenstein Institute in Germany, who will lead this revision with BTTG participation, indicates that both the testing procedure and the apparatus specification will need improvements. This revision will involve inter-laboratory trials of proposed changes to determine if they improve reproducibility and is expected to plan for a 36 month programme.
Revision of ISO 9150/EN 348 – “Protective clothing – Determination of behaviour of materials on impact of small splashes of molten metal”
Yet again this is a test method that needs to have improved reproducibility but also an update of the method of creating the splashes of molten metal, currently by means of a gas welding torch, a procedure not representative of current welding techniques.
Work will begin, again led by Hohenstein Institute and will commence when they have completed work on the revision of another standard – see below.
Revision of ISO 13506 – Manikin fire test for protective clothing – As Part 1 and 2 This test method for determining Burn Injury Prediction (via Part 2) or Transferred Energy (via Part 1) is in the greatest need of being able to demonstrate much improved reproducibility of any test method in the heat and flame sector. Burn Injury Prediction results from the last interlaboratory trial of industrial coveralls and clothing for fighting fires in structures (EN 469 compliant) showed that participants were not subjecting the test clothing to the same heat energy challenge (from a gas burner array) as demonstrated by the images of the tested items. Variation of this key parameter must be a major contributor to the very poor reproducibility.
A massive programme of work is being undertaken by the ISO committee responsible for this test method aimed firstly at establishing that each testing laboratory taking part in this work is challenging the clothing on its manikin with the same amount of energy from the burner flames, expressed as heat flux. When this step is achieved the comprehensive trials between the laboratories can commence – these will involve testing three types of industrial coverall using a three and four second flame application duration and one type of structural firefighting clothing using an eight second flame application duration.
The hope is to be able to revise this standard so that three different types of heat sensor can be used, as represented currently in the more than 20 testing laboratories undertaking this ISO test worldwide, and produce acceptable consistency of results. These trials are planned to take place this year.
Product standard revisions
EN 469:2005, the product standard for clothing for firefighters fighting fires in structures, is being revised to become EN 469 – “Protective clothing for firefighters – Performance requirements for protective clothing for firefighting activities”.
The final draft has been prepared and the voting by CEN member states should start in April 2020. Although there can be no guarantee of a successful outcome from this vote, history shows that very few revisions fail at this final stage.
There are very few changes to the performance requirements so those for heat transfer and water vapour transmission will not change despite clothing being in widespread use that has increased performance for these properties. The UK delegation to this committee, led by the author of this article argued for this revision to reflect this fact – that technology has advanced considerably since 2005 and this should be reflected in raising the minimum performance values for at least these key protective properties. However, the UK received no support from other nations’ delegations.
There are some changes – now only protection against two chemicals, Sulphuric Acid and O-Xylene, required; tensile strength increase from 225N to 300N; tear strength increase from 25N to 30N.
The manikin fire test remains as an optional one, the method referenced being ISO 13506-1 for Transferred Energy, not a measure for which there is much experience or understanding. However, there is a note saying that users “can receive ISO 13506-2 results that they are more familiar with”, that is for Burn Injury Prediction. No performance requirements are given for either Transferred Energy or Burn Injury Prediction because any discussion will need to await the outcome of the work mentioned above about efforts to improve reproducibility.
There are, however, some very important new annexes in this revision draft – on how to express test results, Uncertainty of Measurement, contamination during use and SUCAM (selection, use, care and maintenance).
Revision of EN ISO 11611:2015 – “Protective clothing for use in welding and allied processes”
This is actually another test method topic – the development of a new test for determining the protection provided by the fabrics used in this type of clothing against Ultraviolet (UV) radiation from various welding processes. The work is led by Hohenstein Institute and is slowly showing improved reproducibility of results between the participating laboratories. If this method is proven, it will be incorporated into this product standard.
Revision of ISO 15384:2003 – clothing for wildland firefighting
For too long there have been three slightly different product standards for this end use but we are now close to having just one set of performance requirements, set out in EN ISO 15384: 2018 and ISO 16073-3:2019. To achieve this desirable outcome just requires EN 15614:2007 to be withdrawn.
Recent standards for fire PPE
In 2000 an ISO committee (ISO/TC94/ SC14) was set up to develop, in the main, a series of product standards for the PPE needed by firefighters for their various tasks. The committee, of which the author of this article was a founding member, has made rapid progress recently under its current chair, Russell Shephard of the Australian Fire and Emergency Service Authorities Council.
Examples of its product standards, in three closely related series for the items of PPE worn for fighting fires in structures, in wildland and for rescue are set out below. There are compatibility requirements included, a very important aim of this committee not yet fully complete. BTTG can undertake the tests and compatibility aspects for a number of these important standards.
ISO 11999 series – for fighting fires in structures:
- Part 1 – General
- Part 3 – Clothing
- Part 4 – Gloves
- Part 5 – Helmets
- Part 6 – Foot
- Part – 9 Fire hood
The parts to be completed are 2 (compatibility), 7 (face and eye) and 8 (hearing) so that there are nine parts (although compatibility may be addressed by an overarching standard in the medium term.
ISO 16073 series
The ISO 16073 series is for fighting wildland fires. It comprises, in the same item sequence, Part 1, 2, 3, 4, 5, 7 (face and eye), 8 (hearing), Parts 6 and 9 to be completed. Note that Part 9 may incorporate a particulate barrier test and performance requirement.
ISO 18639 series
The ISO 18639 series is for rescue activities undertaken by firefighters.
In the same item sequence, this comprises Part 1,3,4,5,6 currently.
This ISO committee has produced and is developing more standards for firefighters such as guidance on SUCAM and one addressing cleaning, inspection and repair of PPE.