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In Safe Hands

Published: 10th Aug 2012

Last year students achieved a record 23 percent at A* level grades at GCSE, the 22nd year of improving grades - almost tripling the rate of top grades achieved in 1988. This continued improvement in grades is attributed to examinations which are less demanding, and to schools seeking to use the easiest examination board.

Clearly if the examination varies according to the board, then higher education facilities must find other means to judge the students’ abilities - leading to the question: Why bother with examinations at all?

With cut resistant gloves we have a similar dilemma, where the standards apparently fail and cause confusion to the end user. We should first look at the standard and then see where the problems arise.

EN388:2003

This is the standard for protective gloves against mechanical resistance.

• Scope - This standard applies to all kinds of protective gloves in respect of physical and mechanical aggressions caused by abrasion, blade cut, puncture and tearing

• Definitions and requirements - Protection against mechanical hazards is expressed by a pictogram followed by four numbers (performance levels), each representing test performance against a specific hazard a) Resistance to abrasion - Based on the number of cycles required to abrade through the sample glove b) Blade cut resistance - Based on the number of cycles required to cut though the sample at constant speed c) Tear resistance - Based on the amount of force required to tear the sample d) Puncture resistance - Based on the amount of force required to pierce the sample with a standard sized point

These performance levels must be prominently displayed alongside the pictogram on the gloves, and on the packaging which immediately contains the gloves.

If a performance level ‘X’ is noted, this means the glove has not been tested for the corresponding risk, or that the test appears not to be suitable for the glove material.

Levels of performance are based upon results of laboratory tests; they do not necessarily relate to the actual situation in the workplace. This standard is applicable to all kinds of protective gloves and/or arm protectors against mechanical aggressions of abrasion, blade cut, tear and puncture. The protective gloves shall also meet the requirements of EN420 and have a performance level of 1 or above for at least one of the four defined properties.

Methods used for abrasion testing

Four circular specimens of the prepared sample are abraded under a known pressure (9KPa) and are checked after 100,500,200 and 8,000 cycles. The resistance to abrasion is measured by the number of cycles required for breakthrough to occur, e.g. when a hole is worn through the test specimen. The performance level is determined by the lowest number of cycles to fail out of four test specimens.

Methods used for cut resistance testing

1. Coup Test - This is the original cut test method. To assess the cut resistance prepared samples of the glove are cut from the inner surface of the glove. During the test a circular rotating blade moves to and fro on the sample under a specified load - the blade rotating in an opposite direction to the movement. The test is complete when the blade cuts through the sample. The end of the test is indicated by electrical contact of the wheel with the sample holder as the wheel cuts through the sample. The sample is tested against a control - which is a cotton fabric (canvas). The control is undertaken before and after the test sample. The same cutting wheel is used for all three tests; the mean of the test results is used to calculate the cut index. This method works by comparing the cut resistance of the glove to a known standard. The method can fail for highly cut resistant materials - the standard material being tested first - followed by the test material, which may blunt the wheel. This will lead to an artificially high reading for the second test material as the wheel struggles to cut through. As the cut resistance is determined by the mean average of the results from the standard material, this will reduce the cut resistance result, leading to a highly resistant material being assessed at a far lower blade cut level than is the case. The index is determined mathematically: Index = (+Average Control Result+ Test Result)/Average Control Result 2. ISO Cut Test - This method, while included in EN388:2003, is an internationally recognised standard known as ISO 133997. This is a newer test method designed to overcome the problems associated with the new and highly cut resistant materials. This method determines the force in Newtons (N) to make a 20mm cut in the sample of the cut resistant glove. Under this test a glove is assessed as being a cut level 4 if it scores ≥13N but <22N, while cut level 5 is ≥22N. The force acting on the sample is varied by adding weights, so the test assesses the actual force needed to make a cut, rather than making a comparison to a known standard material. The test makes use of a fresh blade each time the test is performed - this ensures greater reproducibility of results and comparison between test sites. See http://www.youtube.com/watch?v=uXoMco6tJiY for a video of both the Coup test and the ISO Cut test. Note: While the EN388 Standard suggests the Coup test is not appropriate for materials that abrade the cutting wheel, the standard does not require the alternative ISO testing method be used. Section 6.2 of the standard merely states that the test is not appropriate for hard materials like chain mail, but does not contemplate other hard material such as glass fibres. As such, it is possible for some manufacturers - while knowing the test is not appropriate - to use it anyway to get a higher score. It can thus be seen that all level 5 gloves are not created equal, because manufacturers may misrepresent how they test their gloves.

Methods used for tear resistance testing

Four test specimens are cut from the palm of four different gloves - two in the direction of the glove from cuff to finger tips, two across the palm width. The test measures the highest peak recorded to tear a pre-cut (50mm) incision. Specimens are tested at a specified tear speed. The performance level is determined by the lowest value of four results. Method used for puncture resistance testing Four test specimens are cut from the palm of four different gloves. The test measures the force required to puncture a test specimen with a steel stylus of defined dimensions. The performance level is determined by the lowest value of the four results. Applications A specialist area for puncture resistant gloves is with utilities, where operatives are required to pick up used hypodermic needles from bins, or the floor, where there is a very high risk of needle stick injury, and possible infection from Hepatitis or HIV. Clearly this style of glove needs good tactility. The standard EN388 probe is 4.5mm. This is not appropriate for hypodermic needles. One company tests their products using a 1.27mm test probe. A different approach to this problem is the use of layers of interlocking plastic plates. Protective gloves - userinstructions With regard to EN420, a warning should be included that gloves should not be worn when there is a risk of entanglement by moving parts of machines (knitted gloves). For gloves with two or more layers, a warning should be included that the overall classification does not necessarily reflect the performance of the outermost layer. Engineered yarns These are composite yarns made of two or more components, such as a para-aramid synthetic fibre and steel, for example. These yarns have allowed manufacturers to produce higher levels of cut resistance without sacrificing comfort or dexterity. Composites can also be stainless steel wire or glass filament and other fibres, such as Nylon, polyethylene or spandex. Cut resistance in knitted gloves is influence by the following factors:

• High strength yarns

• Hardness (dulling) an example of a hard yarn is stainless steel, which is often a primary component in composite yarns

• Lubricity (slickness): some slippery yarns allow a blade to slide over their surface without cutting through

• Rolling action (knit construction): most knit gloves allow the individual yarns to ‘roll’ as a sharp edge slides over them, producing a sort of ball bearing effect - the edge slides across without cutting through the material Typically, the more of the above factors that can be engineered into a yarn, the more cut resistant it will be. For example, an engineered yarn may consist of high molecular weight polyethylene (HMPE), which is both high strength and slick, and stainless steel which is hard, and then knit into a seamless glove, which provides ‘rolling’. Taken together, these characteristics result in a material that is far more cut resistant than a material made with one component. Further design considerations may be colour, grip, moisture management, or other characteristics that engineered yarns can provide in special purpose gloves. Engineered yarns are typically used in applications requiring the highest levels of cut resistance, such as handling sharp or heavy metal sheeting, handling glass or meat processing where sharp blades are used. Other than chain mail gloves, an engineered glove achieves the highest level of cut resistance. Understanding cut protection We have seen that gloves can easily be tested for cut resistance. This is only part of the story, however. Considering purely cut resistance in isolation misses the wider issues of cut protection as a whole. Let us initially dispel the myth that some hand protection is cut proof. It is true that significant advances have been made in cut resistant technology, affording greater degrees of cut resistance, but it would be a misconception to categorise any hand protection as cut proof. Cut resistance is the key terminology in our discussion on protective gloves.

Other characteristics

There are a number of other characteristics that are important in evaluating cut protection and choosing gloves. These include:

• Grip - The importance of grip becomes clear when you consider that sharp-edged objects pose a much greater threat when they are in motion. A secure grip when combined with the proper level of cut resistance can significantly reduce the chance of injury by preventing slipping and slicing, decreasing the grip force required during a task, and providing the wearer with more control There is no standard method for evaluating grip, although one manufacturer has independently developed a standard, which I believe is important to enable users to compare differences in grip between products The methodology is simple but effective: install a pole vertically on a circular base or similar support. Ballast the pole with enough weight to make it hard to lift. If you wish to demonstrate oil grip, lubricate the pole with an appropriate grade of oil Have the test subject try on several gloves and attempt to lift the pole while wearing each of them. Differences in the required grip strength and the feeling of hand fatigue when lifting the pole in a controlled manner while wearing the different gloves will be readily evident Clearly a better grip can improve other properties in addition to cut protection. A reduction in grip force means a reduction in work effort by the individual. This improves workplace ergonomics and can have a very positive effect on the reduction in repetitive motion injuries

• Abrasion resistance and durability - These are both important factors when choosing cut protection gloves. Most products are used for extended periods, and it is important to ensure that they provide the same level of protection at the end of a shift as they did at the beginning

• If a glove fails too early due to wearing through from an abrasive hazard, the skin is quickly exposed to cut hazards. As such, the higher the abrasion level, the higher the level of protection from not just abrasion, but from cuts and punctures

• Dexterity and comfort - These factors will also be important in some workplaces where small sharp objects must be handled, or the gloves need to be worn for extended periods of time. Comfortable hand protection products that are easy to use mean that workers are more likely to use the recommended hand protection product

• Fit - Gloves that are too tight may be cut more easily, as many of the fibres used for cut resistance use a rolling action to increase cut resistance. When these fibres cannot roll, as, for example, when they are stretched from an ill-fitting or wrongly sized glove, they lose some of their cut resistance

• Coating - This impacts on cut resistant gloves that use cut resistant fibres. Once the coating is applied, the rolling and twisting that helps the fibre achieve its cut resistance can be reduced. Most coated gloves have a higher cut resistance on the back of the hand than the palm because the fibres are not coated. Keep this in mind when selecting a glove

• Other hazards - Some gloves may be worn for more than cut protection. In assessing the protection requirement consider high temperature or chemical hazards

Conclusions

The standard EN388 provides considerable help in assessing the correct glove for your individual application. As discussed above, there are many variables affecting glove choice, however. As cut resistant gloves can be relatively expensive, the wrong choice will be expensive in the cost of the product, but could be even more costly in terms of giving inappropriate protection. The major glove companies train staff to take account of all of the relevant facts and provide the correct advice. Some even offer onsite glove assessments with a product specialist. Remember, the correct cut resistant product is a real investment in your valuable workforce, ensuring not only your employees but your company is protected.

Published: 10th Aug 2012 in Health and Safety Middle East

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Brian Smith