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Seams Absurd

Published: 01st Mar 2010 in OSA Magazine

Evaluating the construction and design of chemical protective clothing is vital in ensuring a selected garment is fit for use. Different garments, whilst being approved to the same European norms may have minor design differences; different width of zip cover, different hood construction and shape, and other such elements which may not be reflected in European Standard testing but may, or may not make the garment more or less suitable for any specific application. One critical aspect is how a garment is put together. 

Users and manufacturers alike have long been aware of the importance of seam construction and type in a garment designed to protect against hazardous dusts and liquids. In simple terms, regardless of how effective is the protection offered by the fabric used, stitching the seam leaves what to a tiny dust particle or low viscosity liquid are big gaping holes - holes which can become particularly exposed and open when the seam is under stress and holes through which these nasty little particles and liquids will readily pass in order to do their dirty work. The laws of the universe tell us that all things will generally take the path of least resistance. Stitch holes on a stitched seam offer such a path through which a little particle such as asbestos might well drive a proverbial bus. Occam’s Razor also tells us that all things being equal the simplest explanation is likely to be the correct one. Thus if penetration has occurred through a stitched seam garment, the simplest and probably correct explanation is that it has occurred through the seam holes.

At the more basic Type 5 and 6 levels... hang on, let’s define terms here for those of us not in the know.

European standards have defined different levels of protection in terms of “Types”. Types relate to different groups of applications with similar properties - for example whether they involve protection against dusts, liquids or gasses, and whether the liquid is in a strong spray or light splash form. The standards identify six Types to cover all eventualities - Type 1, Type 2 and so on down to Type 6. In general terms Type 6 is the “lowest” protection level, namely “reduced liquid spray protection”.

(A classic Type 6 application might be paint spraying. I say “might be” because of course as those hip boys of the once popular beat combo The Monkees so eruditely informed us in the song of the same name, the world is not black and white but full of “Shades of Grey”. In other words there are invariably so many variables in any individual application you care to name that is difficult to be definite and specific about the parameters of any application. Hence all protective clothing recommendations come with a disclaimer stating that it is the users’ final responsibility to ensure the garment is suitable for the application).

Type 1 of course is the highest level protection being “gas tight” suits fully encapsulating suits which are completely sealed against the environment. Type 2 is a similar construction but defined as “non-gas tight” and requiring a positive pressure to be maintained inside the suit by means of pumping air into it. In between the two extremes are various levels of liquid protection - relating generally to the spray intensity and volume of liquid. The odd one out is protection against hazardous dry particles (that’s dust to you and me) and is defined as Type 5, for some reason which I have never been able to fathom, plonked unceremoniously between Reduced Spray Protection (Type 6) and Spray protection (Type 4).

By now you have probably and quite sensibly gone off somewhere to make a cup of tea or find something else to think about, being quite bored of the whole business, so to make things easier I’ve generously summarised these Types for easy reference in Table 1.

These specified types of protection - Types 1 to 6, are all defined as “Class 3” products in the overall classification for all Personal Protective Equipment (PPE). Class 3 are “Complex” products, those designed to protect against hazards. As we saw above, for protective clothing the highest number (Type 6) is the lowest level of protection and the lowest number (Type 1) is the highest, and so of course these overall PPE product classes follow the same logic. Well actually no they don’t ... in fact, in this higher overall classification, Class III, the highest number is the highest level of protection and Class 1 (“Simple” products, relating to PPE not designed to protect against hazards), the lowest number, obviously, yet confusingly, given the way it works with Types, is the lowest level of protection.

Did you get all that? This is the point at which Stan Laurel would very probably have paused, scratched the crown of his head, looked at Olly and said, “... just run that by me again...”. No don’t go and make another cup of tea or we’ll be here all day. It might be a good idea to re-read the last two or three paragraphs just to make sure we’re all singing from the same hymn sheet as it were. As you’ve just had one I’ll take this opportunity to go and make myself a cup of tea whilst you do so. Let me know when it’s all crystal clear (you can then explain it to me!!!)...

Bizarrely, and whilst not directly related to the particular subject discussed in this article, it is worth mentioning that the classification of individual fabric properties of garments, things such as tensile strength, puncture resistance, chemical permeation etc, reverses the numbering system again so that the highest “class” is the highest protection level. In summary:

• In overall Product “Classes”: Classes I to III The highest class number = Highest Protection

• In application “Types”: Types 1 to 6 The highest Type number = Lowest Protection

• In fabric property “Classes” Classes 1 to 5 or 6 (depending on the property) The highest class number = Highest Protection

Simple isn’t it? Some would say this is an excellent system to group and classify product and application variables; On the other hand I would say that it’s an excellent example of what happens when you ask a large committee, often consisting of members with vested interests, to develop something. 

The garment most commonly used are of course those for Types 5 & 6 applications, and here the holes created by stitched seams are not in most cases critical, although the relative weakness of disposable materials means that poorly sized and / or poorly designed garments can result in problems when resultant stress on the seams opens up stitch holes allowing ingress of harmful dusts or liquids. This is something users should bear in mind when considering very low priced garments. The major cost component of a disposable coverall is the fabric, and low prices are too often achieved simply by making the garment smaller and using less fabric - this can be an issue of safety as well as of comfort and durability.

Furthermore, the effect of stitch holes in seams can be exacerbated in coveralls constructed from non or low breathable fabrics (as many are). Such garments will almost inevitably suffer from The “Bellows Effect”. This is a result of the movement of the wearer, walking, climbing or indulging in any other normal working activity which causes the air inside the suit to shift around if cannot escape through the fabric. Consequently, continuous minor changes in air pressure inside the suit occur, resulting in a “sucking” and “blowing” action through cuffs, ankles, zip openings and of course, stitch holes. In applications where protection against dust is required (i.e. Type 5 applications) this can be a significant factor. Dust particles, particularly very fine ones, tend to float freely in the atmosphere moving with any air currents present. Thus they can be drawn through seam holes with the sucking action of the bellows effect. I have seen workers emerge from factories using “carbon black”, a dust so fine that it almost flows like water, and remove their coveralls to find lines of little black dots on their white shirt beneath where the dust has been sucked through seam holes by the bellows effect. It is for this reason that taping up of wrists can be important in some Type 5 applications - basically to try to seal the gaps at the wrists... though of course taping up wrists doesn’t help with stitch holes in the seams.

The seam type for garments used for Type 3 & 4 applications however is far more critical. Such applications often relate to situations where workers may be exposed to splashes and sprays of hazardous liquids such as acids and carcinogenic materials.

Yet the original 1995 Type 3 and 4 standard (EN14065) failed to recognise this and defined these garments in testing terms purely by use of the finished garment spray test rather than a specific test on seams. Some manufacturers quickly discovered that in some cases garments with bound seams could pass a Type 4 test. As a result several such garments became approved to Type 4. I’ll repeat that. Garments constructed with stitched seams, seams that have holes in them, could be quite legitimately used to protect the wearer against splashes of, for example, sulphuric acid. Such garments have even been specifically marketed in some cases as suitable for protection against hazardous chemicals and become widely used in the chemical industry. How could this be?

The standard for Type 3 & 4 coveralls features two key tests:

• Permeation tests of chemicals on the fabric to indicate the fabrics’ ability to act as a barrier against that chemical (four chemicals were specified). The test used was originally EN 369 (though this has now been superceded by EN 374-3) to identify the time taken to achieve a specific permeation rate or breakthrough time against the specified chemical.

• A whole suit spray test, in which a test subject enters a spray booth and is sprayed with a specific volume of liquid at a specific surface tension and for a specific time to check if there is any penetration. It is important to note that some penetration is allowed in this test, controlled by using a calibration measurement on each test. The reason for this is that liquid surface tension and droplet size can impact on the test results, so a calibration linked to that test allows for this. This is also a recognition that the tests are fallible and not a true indicator for all applications. This is why “Types” are a guide and not a definitive answer to coverall selection. Knowledgeable and experienced manufacturers can help sort through this when users work with them.

Unfortunately however, there was no requirement in the original standard for any permeation test to indicate the ability of the seam to act as a barrier to the chemical... which if you think about it is a HUGE omission. Knowing that the fabric can hold out sulphuric acid is somewhat irrelevant if the seams have holes in them. Furthermore, as I have mentioned, the Type 4 whole suit test was (I think unintentionally) structured so that it allowed some garments with stitched seams - namely “bound” or “serged” seams to pass.

What is the difference between a stitched seam, a bound seam and a sealed seam? The pictures above show the difference graphically. You will see from these that in some senses a bound seam is a seam that pretends to be sealed when it isn’t. I have seen one manufacturer in literature claim jauntily that the bound seam on one of their garments provides “impermeability to liquids”. Erm... sorry but no it doesn’t. A bound seam provides impermeability to liquids in the same way that a sieve is a good container in which to carry cornflour.

In a standard stitched or overlocked seam the edges of the two pieces of material are brought together and stitched as in figure 1. The seam may be on the inside or the outside of the garment, and there are arguments for and against both. In a bound seam however a separate strip of material is stitched around the seam - normally on the outside - as in Figure 2. The result is a tougher seam - not necessarily stronger - the strength is more likely to relate to the fabric strength which at the seam is always weaker than the fabric itself because the stitch holes act like perforations in a tear out page - but a seam that is more resilient to damage from abrasion and one that features arguably and marginally improved particle and liquid repellency.

A bound seam is undoubtedly superior to a stitched seam. It is certainly much neater. However, no matter how you dress it up you cannot escape from the simple fact that it is undeniably a seam with the same flaw as any other stitched seam. It has holes in it. No matter that the additional binding may reduce the tendency for the holes to be “opened up” by stress or that it may eliminate the direct path through the seam between the two pieces of fabric; it has been constructed by threading yarn through it with a big steel needle, and those holes can open up and can allow penetration of liquids and dusts, particularly given that these garments are constructed with low cost disposable fabrics which inevitably are comparatively weak. The suitability for such seams in Type 4 garments therefore - garments that may be used for protection against very hazardous liquids - is at the very least, questionable. (Of course, some might argue that a Type 4 garment would never be used for protection against such dangerous liquids and that this is the key difference between Type 3 and 4. But then if this is the case, why does a Type 4 garment fabric need to be tested against specific chemicals in a permeation test - in just the same way that a Type 3 garment is? And in any case, the fact is, such garments have become used in such circumstances.) In fact there have been two methods developed of making seams on disposable Type 3 and 4 coveralls truly impervious to liquids and dusts. One makes use of ultrasonic welding, the other of stitching and taping.

Ultrasonic welding uses high frequency sound to set up molecular vibrations in the fabric that generate internal heat as the two pieces of fabric pass through a roller mechanism. The heat melts the fabric and seals the edges together. It’s as simple as that. Actually it’s not simple at all. Ultrasonic welding can produce effective and strong seams. However, when used on disposable fabrics, which are necessarily and deliberately thin and therefore don’t provide the welder with much material to play with the parameters between “undercooking” and “overcooking” the seal are exceptionally fine. Ensuring precisely the right mix of power, speed and pressure over time can be quite difficult, yet this is exactly what is required to ensure a good seal. A slightly undercooked seam may not be sealed properly, whilst an overcooked seam tends to be inflexible and brittle. More worrying still, either fault can, on casual inspection, seem quite acceptable yet disguise the fact that they may be weak and / or brittle and may simply part at any time under the slightest stress. Furthermore, most Type 4 fabrics feature two or more dissimilar materials - commonly a polyethylene film with a polypropylene substrate. Sometimes there can be several materials and films in a fabric construction. Different materials will be difficult to weld together and will often not weld at all. This may cause further inconsistencies and weaknesses in a weld that are not apparent until it fails.

Moreover, welded seams, whilst potentially having good tensile strength, may suffer from a tendency to tear along the seam too easily once damaged - especially if the seam is a little “overcooked”. Hairline cracks in too brittle a welded seam are another potential pitfall. An apparently perfect seam under close scrutiny can display hairline cracks through which liquids might wick. Importantly, none of these problems are necessarily visually apparent in the finished garment, making quality control through standard visual inspection very difficult. The superior method of sealing seams is through stitching and taping by which as the seam is stitched a “tape” of a secondary material - ideally a chemical barrier tape, is welded over it. Undoubtedly the use of stitching and taping removes all of the variables and potential inconsistencies inherent in ultrasonic seaming.

Thus stitching and taping has been the method adopted widely for lightweight Type 3 and 4 chemical protective garments. However, the Type 3 & 4 standard was revised in 2005 and this has not only lead to confusion in the market place about some Type 4 garments, but the whole business also throws a somewhat sobering spotlight on a generic weakness of the CE standards themselves.

Standards for Type 3 and 4

As we have seen, the original 1995 version of EN 14065, the standard for Type 3 and 4 applications allowed some garments with bound or serged seams to be certified to Type 4, despite the fact that they intrinsically feature stitch holes in the seams. Thus the actual dividing line between the Types 3 and 4, that which defines each type, has been a little vague. The 1995 standard only distinguished them through the varying parameters of the finished garment spray test, the distinction being that the test for Type 3 garments involves a strong jet of liquid directed at seams and closures whereas Type 4 involves an overall spray of a liquid sufficient to result in “pooling” in folds and creases.

The practical result was that whereas Type 3 always required (and requires) a fully sealed seam of some type, in some cases a bound seam garment was able to successfully negotiate Type 4 testing and approval. Yet in recognition that such suits are often used for protection against hazardous chemicals, EN14065 also required a permeation test on the fabric against four specific chemicals, whilst many users demand, and manufacturers provide, permeation tests on a range of other chemicals that they may be using. The fault in the 1995 standard was that it failed to recognise the importance of seams in such applications (beyond the demands of the finished garment spray test) and thereby to enforce a similar permeation test on seams, thus allowing what I have always felt to be a confusing uncertainty in the different performance requirements of Type 3 and 4 garments. Fortunately, when revising the standard for the 2005 version, someone involved obviously felt the same about this as I did because a fundamental change was made; the uncertainty over seams was addressed, simply by requiring a permeation test against at least one of the specified chemicals ON THE SEAM as well as on the fabric, thus ensuring the user can see that the seam has a similar or suitable barrier at the seam as well.

Further, the seam test must achieve a minimum performance level of at least Class 1 (i.e., more than ten minutes). As a consequence of this change, any Type 4 garment with bound seams currently on the market IS NOT APPROVED TO THE 2005 VERSION OF THE STANDARD - but only to the old 1995 version. With their current construction such garments cannot ever be approved to the latest version because a bound seam will inevitably fail a permeation test dismally… because it has holes in it. The permeation test measures the rate at which a chemical permeates the seam at a molecular level. It is simply not possible for any type of stitched seam, bound or otherwise, to meet this minimum ten minute performance level against any meaningful chemical. There are at least two such garments on the market - garments that feature bound seams and which in the last two years or so have claimed to be approved to the 2005 Type 4 standard. Both are from major European manufacturers.

I have seen recent literature from one manufacturer that claimed there was no requirement for permeation tests on seams and closures. In order to check this for my own piece of mind I have clarified this with a Notified Body, and just in case there is any lingering doubt in your mind, here is a quotation from the standard itself:-

Excerpt from EN 14605:2005, section 4.2

“4.2 Seams, Joints and Assemblages Seams, joints and assemblages shall be tested and classified according to the requirements of Table 2 and the corresponding clauses of EN14325”

This is unequivocal. The standard clearly requires a chemical permeation test on “exposed” seams (which let’s be honest is most of them) and clearly requires a minimum performance of class 1. The reference to EN 14325 is the standard that defines the classes for all the fabric properties; Class 1 is a performance of more than ten minutes. In other words the seam must be tested and must achieve a normalized breakthrough time of more than 10 minutes.

Obviously the implication of making such fundamental changes to standards is that the date of the standard to which a garment is certified is now just as important as the standard itself. The standard for labelling requirements recognises this and CE labelling now demands the relevant pictogram is accompanied by the standard number AND DATE. Yet in a personal small scale survey of Type 4 garment samples at a recent major European safety show, none of the garments on display that I checked showed this information on the label with the exception of one… and again, all were from major European manufacturers.

In order to prove my point I went to the trouble of obtaining a couple of Type 4 garments from the market place and arranging independent permeation tests on the seams against 30% sulphuric acid - one of the chemicals specified in the standard. In each case seam samples were taken from different parts of the coverall for testing. The results are shown in the Table 3 below:-

This is pretty conclusive. Garment 1 was a microporous film laminate fabric with bound seams. Its user instructions clearly claimed that it was approved to the 2005 version of the standard. Garment 2 was a garment of similar fabric with a solid film barrier tape sealed over the stitching. In every case, the permeation time on the former garments’ seams was less than one minute, whereas in every case the permeation time on the latter was more than 30 minutes.

Clearly, garment 1, despite its accompanying information claims to the contrary, can only be certified to the old version of the standard. I suspect and hope that there is no deliberate attempt to mislead users here but rather that this is a result of a failure to review and understand the new standard sufficiently and that the manufacturer has simply added the date of the new standard to the label without checking if this is correct. Here is another reason for working with manufacturers who do know what they are talking about.

The critical issue here from the perspective of the protection offered, is that those Type 4 garments with bound seams are actually providing a lower level of protection than their apparent CE marking suggests. For a user who has a good understanding of the standards, it is reasonable to assume that a garment is approved to the latest standard if it says so. The nature of bound seams however and the tests above show conclusively that this is not so. A hazardous chemical that may, for example be carcinogenic, might readily and quickly permeate through a bound seam, even though it is apparently approved to the current Type 4 standard, which requires a minimum performance level of greater than 10 minutes.

The thing that disturbed me most about this situation however, and the reason why I said earlier that the whole business throws a sobering light on the whole CE marking system is this. When a standard is revised or upgraded, even where there is a substantial and real change in the performance requirements, there is no requirement for manufacturers of existing products on the market to upgrade their products to meet the new standard, even if they clearly don’t. Admittedly, they must (or at least should - as far as I have seen most don’t) show that their product is only approved to the old standard through the use of the standard date on the labelling, but they don’t actually have to make their product meet the latest standard. Ever. Manufacturers can literally and quite legally continue to produce and sell a product that only meets an old version of a standard indefinitely.

Think that through again. Standards are regularly (or at least as regularly as can be achieved in such a cumbersome system) upgraded to improve them or ensure they are providing adequate protection. Yet manufacturers don’t actually have to meet the new standard if they already have a product certified to the old one. They can carry on regardless, willy-nilly claiming certification to an old standard which the authorities, simply by the process of introducing an improvement to it, have told us is not good enough.

This situation could be remedied easily enough by including a “sunset clause” in the standards. Such a clause specifies a date after which manufacturers may no longer product garments to the previous version of the standard. The inclusion of a “grandfather clause” would allow for the sale and continued certification of all products that are currently in distribution channels or in end user inventory at the date of sunset. Problem solved and end users would not need to get into the “weeds” of standards revisions.

Even if the date difference is made clear in the labelling, how many end users are likely to understand the finer differences between the 1995 and 2004 versions of the same standard? I have seen many situations where users just take the view that if it is approved to a standard that’s OK and they don’t have to worry about it. On several occasions, even when explaining this issue over seams to users, it has clearly become too complicated to think about and they understandably take refuge in the claim that as long as the label says it is Type 4 then they’re happy with that. Of course, they are likely to be rather more concerned when one of their employees is burned by sulphuric acid that has penetrated through a stitch hole in less than one minute...

The wider context here is that I consider it a real and serious failing of the entire CE marking system that a substantial change can be made in a standard, a change that makes a major new requirement on a product, and yet products approved to the older version do not have to re-certify to the new. It does not take a great leap of imagination to envisage a situation where a user makes use of a product quite reasonably thinking he is getting a higher level of protection than he really is. The potential for danger is clear to see. How much more sensible would it be to include a “sunset clause”, for manufacturers marketing an existing product to be given a period of time, perhaps a year, to ensure their product meets the requirement of the new standard.

(The other effect of this whole thing of course is that manufacturers introducing a new and better product can be disadvantaged because meeting an upgraded standard may well mean a higher product cost having to compete against existing products that have a lower cost but only because they only meet the old standard. This applies in the case of bound and taped seams. It is much cheaper to produce a bound seamed than a taped seam garment.)

I am sure the reasons for this failing of the CE system are benign. It may well be a result of a genuine wish to avoid imposing unnecessary costs on manufacturers (although if this is a genuine concern it might be an idea to consider capping the charges made for certifying products). Admittedly it may seem harsh to make a manufacturer change an existing product because a standard has changed. On the other hand ifthe previous standard had failings in it that required changing - as had the original Type 4 standard - then surely it is not unreasonable to expect manufacturers to meet the new standard as well provided they are given a reasonable time in which to do it? We are after all talking about potentially saving lives here - or rather about potentially not saving them. Some might argue that the current system allows the flexibility to allow manufacturers to provide a variety of choice to customers by adhering to different versions of the standard. I would argue however that this, as I suggested earlier, is precisely what results when you employ a committee consisting of various conflicting interests to design something. In such situation the result will always inevitably be the lowest common denominator. Like sulphuric acid passing through the stitch holes in a bound seam, the result will always take the path of least resistance... 

Seams ridiculous to me... 

Author Details:

Martin Lill

Lakeland Industries Europe

Wallingfen Park


East Yorkshire

HU15 2RH


Tel: +44 (0)1430 478140


For more information on Protective Clothing http://www.osedirectory.com/product.php?type=health&product_id=17

Published: 01st Mar 2010 in OSA Magazine


Martin Lill

Martin Lill is General Manager of Lakeland Europe, the European & Middle East divisionof one of the world's largest manufacturers of disposable protective clothing.  He has over fifteen years experience in the industry and would be happy to answer any questions.  


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