All About Cut Resistance
All edges are sharp. However, a true assessment of this hazard can help reduce costs both in procurement and by reducing cut incidents.
- By Griff Hughes
- Jun 01, 2004
RECENT studies by two sheet metal manufacturers placed the cost of a single hand injury requiring stitches at $22,000 and $30,000, respectively. The cost estimates included: shutting down the assembly line in order to remove the injured worker; cleaning the area; medical costs including ambulance transportation; and rehabilitation.
If these estimates are correct, preventing hand and arm injuries with cut-resistant gloves and sleeves can be very cost effective.
In general there are two types of cut hazards:
1) Clean, sharp edge cuts, such as knife blades and clean edge sheet glass.
2) Abrasive cut hazards. These include: rough edge sheet metal; stamped or punched sheet metal; and rough edged sheet glass.
Clean Sharp Edge Hazards
Our industry currently measures cut resistance for clean sharp edges with the Cut Protection Performance Test (CPPT) on ASTM Standard F1790-97. This test measures the weight (in grams) required to cut through a glove on a 25 millimeter pass using a razor-sharp blade.
In order to make cut-resistant gloves for this type of hazard, we, as an industry, design the following factors into the yarns that are used to knit our gloves:
1) Tensile strength. The strength of the fiber is so great that it cannot be broken. Stainless steel has this capability.
2) Abrasive action. The fiber is so hard that it will dull a passing metal blade. A glass core can provide this feature.
3) Slippage. The blade actually slides across the yarn without catching to cut. Certain monofilament fibers have this advantage.
Gloves that are designed to resist clean edge cuts are usually made with core yarns. Core yarns are manufactured by wrapping different yarns around a center or solid fiber core. Each wrap provides a factor of cut resistance. When evaluating cut-resistant gloves, a user should ask for the CPPT rating of the glove, its fiber composition, and which factor of cut resistance each yarn provides.
For example, an accident occurred where a glove with abrasive action and slippage provided the protection necessary to handle the sharp edge on a curled ring of metal. Unfortunately, it was not mentioned that the worker sometimes had to pull hard on this ring to pry it lose. Without tensile strength incorporated into the glove fibers, the glove failed.
Core yarns are the most expensive to make because each wrap requires a pass through the machine and most yarns have multiple wraps. Weight or thickness of this type of glove should not be taken as an indication of cut resistance. The outer wraps of core yarns are usually some form of polyester. Adding multiple layers of this product can make the yarn appear stronger without adding any appreciable protection against cuts. The CPPT rating will always give the user an accurate measurement for cut resistance.
Because of their high cost, these types of gloves are primarily used as liners in industrial, food, or laboratory applications with the cover gloves providing the appropriate wear capabilities.
It should be strongly noted that these gloves cannot protect against moving or rotating blades or serrated edges. Moving blades will eventually cut through any glove, and serrated edges can penetrate the finely knit cloth and cut the hand.
Abrasive Cut Hazards
At present, there is no test to measure abrasive cut resistance in gloves. The ASTM F1790-97 standard is often used as a reference point, however, we must keep in mind that this standard tests with a razor-sharp blade. Abrasive cut hazards do not just cut, they tear and abrade and consequently require a different type of glove for protection.
Gloves used in these areas must provide cut resistance, along with the additional requirements for abrasion resistance and tensile strength. They also tend to be much thicker, in order to resist the rougher edges, and are used in direct contact with the hazard rather than as a liner.
Certain factors are incorporated into the design of these gloves:
1) Stretch. This allows the glove to move ahead of the cutting edge. This is why most cut-resistant gloves are knit and not woven.
2) Rolling. The yarn fibers roll as the edge passes across. An analogy would be cutting a carrot with a knife. If the carrot rolls it will not cut, but when held stationary it cuts very easily.
3) Loft. A soft thickness in the glove that resists a cutting edge. We can cut a piece of paper very easily with a sharp blade. However, if we place the paper on top of a pile of shaving cream, the task becomes more difficult because we lack the pressure required to cut.
When evaluating abrasive cut hazards, we need to separate them into physical application categories:
All edges are sharp, however, a true assessment of this hazard can help reduce costs both in procurement and reduction in cut incidents. There are many different types of cut-resistant fibers to choose from, and each has a cost and/or protection benefit that can be evaluated.
Thin gauge sheet metal has a smaller burr when stamped or punched than thicker gauge sheet metal. Bigger burrs or rougher edges require thicker or heavier weight gloves. The thickness will prevent the burr from penetrating the glove and cutting the hand. Heavier weight gloves will wear longer when exposed to rougher edges. Yarns with higher tensile strength combined with abrasion resistance are required in these applications.
Dry surfaces require gloves with grip. Oily surfaces require gloves with absorption in order to get a good grip. Different grips can be added to cut-resistant gloves by dipping, dotting, or screening.
Punctures are often categorized as cut hazards because they cause lacerations. When dealing with this type of hazard, it is important to remember that the initial protection needed is not cut resistance, it is puncture resistance. The hand is getting cut because the barb or shard is penetrating the surface of the glove. A coating or leather patch can be added to the glove surface to help prevent shards from penetrating.
Moving edges versus stationary edges
Moving edges require thicker gloves because the edge tears the glove surface as it passes along the palm. Thickness, in this case, equates to wear resistance. Stationary edges require less reinforcement. It is important to note the moving edge referenced here occurs when a hand slides along a piece of metal or glass as it is grabbed. No glove can protect against a moving or rotating blade.
Hand cut injuries often occur in sheet metal assembly areas where moving parts (nuts, bolts, and screws) are driven with automatic wrenches and screwdrivers. As a general rule, knit gloves should not be used in these areas because they can catch on the edge of a turning screw or bolt as it is driven. Gloves with a tacky grip can pose the same hazard. Gloves knit with cut-resistant fibers can be dipped with coatings that encapsulate the knit fibers and provide dry, wet, and oily surface gripping without being tacky.
Useful Terms to KnowThere are many designs of cut-resistant gloves, however, most are knit. The following terms may be helpful in understanding how these gloves are made.
- Gauge. In knit gloves, this refers to the weight or thickness of a glove. Technically, it is the measure of the number of wales (vertical knit lines) per horizontal inch. For example, 7 gauge means that there are 7 wales per horizontal inch. This allows the knitter to use a thicker yarn in order to make a heavier glove. Cut-resistant gloves are available in 7, 10, and 13 gauge weights, with 7 being the heaviest.
- Plating (or plaiting). This occurs when two gloves are knit together simultaneously. The outer glove can be made with one type of yarn and the inner glove with another. Thus, certain features can be added independently in order to meet the user's needs. Plating has the additional advantage of making a glove thicker, which can be a useful design feature when dealing with punched or stamped sheet metal.
- Terry cloth. This term refers to gloves that are knit with a loop structure. The loops are aligned along the width of the glove so that any edge cuts along the length of the yarn. Anyone can cut a string in half, but try cutting along the length of the string. Even with a razor blade, it is extremely difficult. This is one of the cut-resistant design features that terrycloth offers. The other is that the loop structure offers the soft, cushioning effect that is so cut resistant.
Get a Second Opinion
In conclusion, our industry produces many different types of glove designs and fibers intended to prevent cut injuries. To choose the proper protection, you must first assess the hazard for all required criteria. After this assessment, you should select a glove based on the feature it offers in both fiber content and glove design.
And, as always, it's advisable to get a second opinion.
This article originally appeared in the June 2004 issue of Occupational Health & Safety.