All About Cut Resistance
- By Griff Hughes
- Jun 01, 2004
All edges are sharp. However, a true assessment of this hazard can help reduce costs both in procurement and by reducing cut incidents.
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:
This article originally appeared in the June 2004 issue of Occupational Health & Safety.