Gloves Against Mechanical Risks

Testing circular and straight blade cut resistance

by Simon Courtney

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General-purpose protective gloves account for the largest market share of all personal protective equipment sold and protects wearers from a wide range of hazards. To assist wearers with the selection of appropriate gloves, several European safety standards – including EN 388:2016+A1:2018 – have been developed, enabling levels of protection against different risks to be defined.

These defined levels of protection enable appropriate gloves to be selected, based on the hazards and risks identified for a specific work activity. One of most common hazards that workers face is the risk of cutting to the hand. Where possible, any risk from severe cutting hazards should be removed from the work activity, for example, by the use of guards, leaving the operative to require protection against only relatively minor hazards from small blades and cutters. Nevertheless, although the potential damage from cutting by a single blade is somewhat less than that from a circular saw or laser cutter, it can still be fatal. The use of cut-resistant personal protective equipment (PPE) should, therefore, always be considered where there is a risk of being cut. Most minor cut incidents occur to the hands, simply because these are normally the parts of the body closest to the operation involving a sharp blade. Other parts of the body can usually be protected by modification of cutting practice or with the use of additional guards, but the hands are (in most cases) required to carry out the cutting operation, and so cannot be completely removed from the process.

“the most commonly used cut resistance tests uses a circular blade to differentiate low to medium cut resistant materials”

European standard

The European standard EN 388:2016+A1:2018 – ‘Protective gloves against mechanical risks’ is intended for gloves with mechanical protection and contains performance requirements for five characteristic elements of protection: abrasion, blade cut, tear, puncture and impact resistance. The abrasion, blade cut, tear, and puncture properties are divided into protection levels and the impact resistance test has a simple pass/fail criteria. The standard contains two tests to demonstrate the cut resistance tests which use different types of blade cut procedures and performance levels.

The first uses a circular blade and the second uses a straight blade cut.

Circular blade cut resistance test

The most commonly used of the two cut resistance tests uses a circular blade and is a suitable test for differentiating low to medium cut resistant materials. In this test a counter rotating blade (under a standard 5N contact force) tracks backwards and forwards over the flat surface of the test material within a fixed stroke length. Where multiple layer materials are present, the layers are assembled and tested as they would be in the glove. A specimen is taken from the palm region of separate gloves and five test cuts are made on each, which allows for any variation across gloves. If the glove possesses other areas of protection then additional tests may also be carried out on specimens taken from these areas. Some gloves may be designed to have areas of higher protection provided by additional panels attached to the glove. These panels provide the glove with a greater thickness in these regions and may also improve the abrasion resistance properties. It is common for these panels to be divided into sections which are smaller than the size of the whole of the glove so that they create a break in the materials which is orientated in line with the natural folds in the hand when it clenches. These breaks allow the glove to fold as the hand bends and makes it easier for the wearer to bend their hand and clench an item. In those regions where these additional panels are divided the original thickness of the glove will be the area that provides the minimum protection. For these types of gloves, the original thickness of the glove must be tested as the area of the lowest level of protection rather than the area of increased protection for cut resistance, and other protective properties if they are claimed. It may be necessary to carefully remove the additional panel to provide an area of sufficient size for a test specimen to be cut from the glove.

The dimensions and suitable suppliers of the test blades are specified within the standard. Prior to testing, the blades are normally too sharp so they need to be prepared for testing by reducing the sharpness of the blade to the required level by performing cutting motions on three layers of a control fabric.

In the test the specimen is clamped in a holder with the slots in line with the cutting action of the blade. This holder keeps the specimen flat during testing and ensures that the test cuts made are at a sufficient distance apart to prevent damage from one section affecting the adjacent test cut. The blade runs in a to-and-fro motion and the test stops when cut-through of the blade is detected (via electrical contact with the underlying surface) or when 60 cycles is reached, and the number of strokes completed by the blade is recorded. The horizontal movement of the test cut is 50 mm long and the blade rotates completely 360° during cutting. To take the sharpness of the blade into account, the test is performed using a standard canvas control material both before and after testing the specimen. A ‘blade cut index value’ is calculated from the number of cycles required to cut through the specimen and the mean number of cycles required to cut through the control material.

Using the circular blade cut test for composite fibre-based materials (including advanced technology aramids) and other specialised materials has its limitations. For all these products, which are designed to achieve high levels of cut resistance, the blades may be dulled during the extended testing. In such cases, the straight blade method specified in EN ISO 13997:1999 is more suitable. Glass fibre and abrasive surfaces may also give variable results between individual cuts as they blunt the blade. Steel fibres risk creating an electrical contact with the specimen holder, thus indicating a false reading in the cut-through point.

ISO straight blade cut resistance test

The second cut test contained within the EN 388 standard is described in the EN ISO 13997 method. In this test a straight blade is drawn across a small piece of the fabric until cut through takes place. The principle of this test is to vary the load required to be applied to the blade in order to facilitate cut-through in a known distance.

A straight blade cut tester consists of a straight blade (of known sharpness) fitted to a carriage, which is capable of horizontal movement to draw the blade across the sample. The sample is mounted on a curved surface. In turn, this is placed on top of a series of levers in order to apply a force from below the sample holder onto the blade, which simulates a mass being placed on top of the blade itself. As with the circular blade cut test the test specimen is taken from the palm area where the least protection is expected. The blade is drawn across the sample at a set speed, with the distance travelled until cut-through (referred to as ‘stroke length’) being recorded. Typically, cut-through is indicated by the point where an electrical contact is achieved between the blade and the underlying holder. Therefore, where test samples include steel threads, it is necessary to place a sheet of thin paper or plastic film between the sample holder and the fabric to prevent electrical contact through the fabric itself.

The test procedure begins by carrying out a number of cuts using a variety of forces applied to the blade to gain a suitable range of cut lengths. This is, typically, five cuts in the range of 5-15mm, five cuts in the range of 1530mm and five cuts in the range of 30-50mm (cut lengths below 5mm or above 50mm are ignored). Using this data, a scatter graph can be drawn by plotting stroke length to cut through against applied load.

From this graph, an estimate can be gained for the applied load necessary to gain a 20mm stroke length before cut-through by plotting a trend line through the data points (an exponential plot often gives a fairly good correlation). Using this estimate, a further five cut tests are carried out, with the graph replotted. If the average of these five cuts is within a suitable tolerance from 20mm (± 2mm), a further estimate is taken from the new graph and recorded as the final result. If the average of the five cuts is outside the tolerance, the new estimate is used for a further five cuts, with the results used for a final re-plot. The final estimate from this third graph then becomes the final test result. The test result is based on the estimated force required to generate a 20mm stroke length, in Newtons.

Blades for this test are made to a specification set by the test method. Each batch is checked for average sharpness, defining a sharpness correction factor. Batches of blades with too low a value for sharpness, or with too great a variation in sharpness, are rejected. When blades are accepted, each batch is assigned with a correction factor, which is used to normalise the results of each cut test. A new blade is used for every single cut test – and discarded after use – to ensure that the test sample is only cut a single time by the blade. In comparison to the circular blade cut test, the blade travels only a short distance, which means that blunting of the blade plays a much less significant part and the test is more suitable for higher cut resistant materials.

Performance levels

In the circular blade cut test a mean blade cut index is calculated for each specimen tested. The performance level is based on the lower mean blade cut index of the two specimens, ranging from a level 1 cut resistance index of greater than 1.2, up to level 5, with a cut resistance index greater than 20, as shown in Table 1. A glove that produces a result which falls below an index of 1.2 would be assigned a level 0.

In the straight blade cut test the cut resistance of a specimen is calculated as discussed above, and a level assigned as shown in Table 2, with results ranging from a level A cut resistance of greater than 2N, up to level F, with a cut resistance index greater than 30N.

Differences between the methods

It is worth noting that due to the differences in the two methods used for cut resistance, there is no correlation between the two procedures and they are better suited to different materials. However, it is widely considered that the ISO 13997 method is generally more accurate for high levels of cut resistance. The trade-off is that due to the need for large numbers of individual cuts (each using a brand new blade), the ISO 13997 method is significantly more time-consuming and therefore more costly to carry out. EN 388 does allow the testing of a glove to either or both procedures and reporting the achieved level to the wearer, assuming they do not show blunting of the circular blade.

“it is widely considered that the ISO 13997 method is generally more accurate for high levels of cut resistance”

Limitations of testing

There are limitations to all laboratory test methods which mean that they are unable to completely reproduce ‘reallife’ situations. The two tests described above use controlled blades where the dimensions and sharpness are closely specified within the tolerances laid down within the standards. These blades cannot represent all possible blade shapes and dimensions a wearer may be exposed to. The cutting procedures including the speed of cutting, angle of contact and cutting forces all being closely controlled. Again, these cannot represent every situation during normal use with speeds, angles and forces all varying from task to task. Testing in accordance with the methods discussed is always carried out on new gloves which have not experienced any wear from normal usage. If a glove can be laundered, EN 388 requires testing both before and after laundering and the claimed level being the lower of the two. The laundering process does not include the use of any soil or contaminant. In these circumstances it is reasonable to expect that new gloves are likely to produce the highest possible results. In normal wear a glove may receive a degree of abrasion which is likely to reduce the thickness and hence the protective properties provided, and hence reduce any likely cut resistance result. The standards also do not take into consideration any contamination which may also affect the gloves performance.

It would be very challenging to develop a testing procedure which would take into consideration the almost endless range of cutting situations a glove may be expected to protect a wearer against. Aside from the development challenge, the level of work required to complete such testing and the subsequent cost would be relatively high.

While it is easy to recognise the limitations of testing it is important to understand the benefits of a simple system with a relatively low testing cost. Both methods described above provide a simple system by which gloves can be assigned cut resistance levels, which allows the wearer to select the most suitable level of protection for the task they are to undertake.

Notified Bodies

With two Notified Bodies, one in the UK and another in the Irish Republic, SATRA has a team of experts on hand to help you through the process of the testing and type examination according to the requirements of the PPE Regulation. SATRA is also able to carry out the module C2 checks on samples from bulk production as specified in PPE regulation, or, alternatively, module D quality management system audits in the manufacturing facility.

SATRA is able to test and certify protective gloves, safety footwear, fall protection equipment, high visibility garments, hearing protection, and protective clothing (including items designed for motorcyclists). Products providing eye, face and head protection, PPE to be worn when engaging in sports or using a chainsaw, and items to protect against heat and flame can also be assessed in SATRA’s laboratories.

SATRA offers a fast efficient service for customers and will also advise on the procedures which need to be followed. For more information, please email ppe@satra.com or alternatively, visit www.satra.com/ppe

Author Details

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Simon Courtney

Simon Courtney is a footwear technologist at SATRA Technology. He has a wide knowledge of testing and supports customers with technical reports, advice and in the preparation of company-own specifications.

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