Dynamic Cut and Puncture – A Different Perspective on Safety

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Dynamic Impact Injuries; Nail Guns and Cut and Puncture Protection                                                                 

At TurtleSkin we design both safety equipment for the commercial market as well as body armor for law enforcement and military customers. These two product programs have significant shared technology and the learning goes back and forth between these disciplines. One of the engineering crossovers from body armor is dynamic cut and puncture. For characterization of the cut and puncture threats we look at the energy of the threat not the force of the threat.

The extended use of the nail guns, power staplers and related impact devices has broadly increased the rate of injury from dynamic treats in the workplace

In body armor testing  we have grouped threats into 3 energy levels, 35, 50, and 65 (E2)  joules of energy.  A joule is a watt-second or 0.74 ft-lbfs if that helps.  These levels were determined by measurement of the energy that young adult men could delivery with their arms. These energy levels are measured at impact when the mass and velocity of the hand and lower arm strikes. If the hand holds a tool or knife the energy at impact is delivered at the tip. In the workplace impact energy can be delivered without power tools.  Our estimates suggest these threats at 5-15 joules. However a 16 penny nail gun is more than capable of delivering nails at energies in the  35-65 joule range, the same as body armor requirements.

When tools slip, when product is dropped, when power tools are in use the threats to workers are dynamic.

The safety market has concentrated on testing equipment for cut and puncture at very slow speeds, by design these slow test speeds eliminate dynamic effects. PPE is measured in units of force to penetrate or cut. PPE tests like EN388 fall into this class.   These slow speed tests result in PPE that has real protection however the protection is not sufficient impact or for power fastening tools.

From the OSHA guide “Nail Gun Safety: A Guide for Construction Contractors”

“How likely are nail gun injuries? A study of apprentice carpenters found that:
• 2 out of 5 were injured using a nail gun during their 4 years of training.
• 1 out of 5 were injured twice.
• 1 out of 10 were injured three or more times.3
More than half of reported nail gun injuries are to the hand and fingers.4
One quarter of these hand injuries involve structural damage to tendons, joints,
nerves, and bones. After hands, the next most often injured are the leg, knee,
thigh, foot, and toes. Less common are injuries to the forearm or wrist, head
and neck, and trunk. Serious nail gun injuries to the spinal cord, head, neck,
eye, internal organs, and bones have been reported. Injuries have resulted in
paralysis, blindness, brain damage, bone fractures, and death”

At TurtleSkin we estimate impact energy threats at  5-15 joules of in construction and manufacturing occupations without power fastening. Nail guns are certainly increasing this threat.

Energy standards include NIJ, HOSDB, and VPAM

  1. Stab Resistance of Personal Body Armor
    NIJ Standard–0115.00
  2. HOSDB Body Armour Standards for UK Police (2007)
    Part 3: Knife and Spike Resistance Publication No. 39/07/C
  3.  VPAM – KDIW 2004 Schutzausstattungen Stich- und Schlagschutz
    - Anforderungen, Klassifizierung und Prüfverfahren

© 2014 Warwick Mills Inc. All rights reserved   DC1070-003-007

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Dexterity the Silent Factor in Glove Specification

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We have EN388 and we have ANSI glove testing. The results from these Cut, Puncture, Abrasion and Tear tests certainly provide part of the picture on glove performance.   Some thing is missing however. With gloves the elephant in the room is dexterity. It makes no difference how protective a glove is if it gets in your way of doing your job.  At TurtleSkin we have been making and selling needle and cut resistant glove for many years.  We have learned by customer purchasing patterns that dexterity is the key to glove acceptance.  Almost every day we hear much the same perspective from Safety Officers: “your gloves have the protection e need but will my team wear the gloves?” So no one says anything about Dexterity but all our customers want gloves that are just that— dexterous.

The problem is that there are only a few tests for dexterity. There is the EN420 Pin Test, The ASTM 2010 pegboard test and there is the Minnesota Dexterity Test. So there are various methods  to choose from to make measurements and evaluate the performance of the gloves. Given that we have methods to test dexterity why don’t we use this data as part of a standard requirement for glove specification? The answer is two part.  Part of the problem is the data from these tests is not simple for customers and Safety  Officers to relate to real work requirements. The second part of the problem is, these tests are based on using human subjects to run the Pin Pickup Test,  Pin Board Testing and the Minnesota Dexterity Tests. In our own program we have worked with these tests and it takes great deal of care to produce repeatable data that is reliable.  When you use human subjects the test subjects introduce variability into the test results.

What are our options?

At TurtleSkin we make a modest proposal. There are two pieces of data that can be used and that are simple to interpret.  The first test is a simple caliper measurement of  the thickness of the glove finger tips. The second test  is a machine based test to measure the stiffness of the glove material, ASTM D4032 for measurement of textile bending stiffness. The sensation and tactile performance of a glove is directly related to the thickness of material at the finger tips. It is obvious that the bending stiffness of the gloves is directly related to their dexterity.   These two tests can easily be related to glove performance and the results are easy to understand.

Thinner gloves with lower bending stiffness have higher dexterity.

We have demonstrated the the value of these the Thickness-Stiffness tests by correlating the results with human subject tests and we get good agreement. The proposed Thickness/Stiffness tests have the advantage that they are easy for labs to run and thus the results can be compared even when performed by different labs. The best way to start your own dexterity specification program is to test gloves that you know your team have accepted as easy to work with. This established your baseline.  Send us 2 pairs of your gloves and we will test them for you and send you the results or test them in your own lab and you can use this data as a starting point for glove objective data driven purchasing.

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Engineered Protection: Composite materials for Cut and Puncture Gloves

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In the Post “Cut and Puncture Resistant Fibers For Gloves (Pick the Right Fibers)” we covered the most common fibers used in cut and puncture gloves. While this review of fiber types is useful you cant select gloves based on fiber type alone. Most advanced protective materials are composite textiles and are made from multiple fiber types and combine other non-fiber materials.

Textile Types 

Knits: The fastest growing glove textile is the knit. This is driven by automated glove knitting machines which allow us to manufacture the basic glove knit shell with low labor content.  Knits have some great advantages for gloves, jersey knit textile has 2 way stretch and stretch is a significant advantage for glove sizing, comfort and dexterity.  Like most things in life knits and stretch come with a down side. The more open the knit and the more stretch the lower the protection will be for both cut and puncture.  Thin comfortable knits with stretch don’t have high fiber content per unit area. This fiber content per unit area is a simple idea for optimizing cut.  the more of a given fiber type your have under the cutting edge the better the cut performance will be.  With regard to puncture this is pretty clear, an open stretchy knit is not a very effective barrier to puncture.  Even large EN388 penetrators just push the knit fiber out of the way and slide right through the knit materials.  Smaller ASTM nail type penetrators and hypodermic needles penetrate knits with no resistance.

Wovens: Many gloves are made from woven textiles,  however wovens don’t have stretch so a glove made from all wovens has to be very carefully designed and sewn to fit well.  Wovens may not be as easy to use a knits but  they are standouts for cut and puncture performance. The weaving process can product a very dense textile with high fiber content per unit area so you get really high cut performance from well designed wovens. Even better we can engineer weaves that have no sliding yarns so these weaves have high puncture resistance even to the smallest 28 gauge hypo needles.

Coating-Knit-Woven Composites 

In the TurtleSkin line we have found that the best marriage for gloves that are both comfortable and protective is to use a composite or laminate of both knits and wovens. We put the high protection wovens in the area where the risks are on the hand. Then in the areas that are not at risk  we use the stretch and openness of the knit to keep the glove comfortable.  This is an important concept in glove selection. Don’t over spec your protection area. If you ask for 100% protection when you don’t really need this much you will end up with a glove that is both more expensive and less comfortable. If you are not getting injuries on the back of the hand then don’t spec in high protection in this area.

The glove design process does not stop with the combination of multiple types of textiles, coatings play a large role. The mechanical strength for cut and puncture resistance is provided by the textile. Grip and abrasion resistance can be greatly improved with a well engineered coating. Soft polyurethane rubber coatings offer some of the best grip and wear performance around.  In addition to grip coatings provide an opportunity to improve cut and puncture resistance.  The coatings can include hard materials and can be engineered to increase the internal friction in the textile so the cut and puncture are improved. Just as in the case of the use of wovens, coatings reduce the stretch and dexterity in the glove so don’t over spec your coating area. Palm and finger tip coating is a great compromise.

Summary

  1. Knits are very important to comfortable gloves because of their stretch.
  2. Look for wovens for improved Cut and Puncture protection
  3. Look at the coating materials: Do they have enough grip and durability

 

© 2014 Warwick Mills Inc. All rights reserved.

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Cut and Puncture Resistant Fibers For Gloves (Pick the Right Fibers)

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A very common mistake in glove selection is picking the wrong fiber type. As you will find from the descriptions below fibers are not all created equal.

When you are looking for protection and make glove purchasing decisions in  addition to the summary information on fibers listed below the assembled textile and coating must be considered.

Talk a look at a separate post: “The  Puncture and Cut Resistant Textiles and Composites”

Polyester

This material is perhaps the most widely used synthetic fiber. Low in cost and available in may sizes and types. Moderate tensile strength and low cut performance limit the protection from this material used  alone.  Polyester yarn in its textured form has quite good abrasion for its price point.  Chemical resistance is broad, however polyester is a moderate temperature fiber with a burn and drip risk. This material is useful as a blending fiber for controlling the cost of a composite yarn.

Nylon

Nylon is the second most widely use synthetic fiber. Nylon has  moderate tensile strength and low cut.  Nylon has really standout abrasion resistance and this makes it very useful in gloves. The military has used nylon in combination with cotton for BDUs and other garments for many years.   Like polyester, nylon is an excellent choice for glove components, it is  slightly more expensive than polyester but higher in durability. Nylon has moderate temperature resistance and a burn and drip risk if used by itself. Chemical resistance is lower than polyester.

Para-Aramid

This is the old stand Kevlar, Twaron, and Technora this fiber is aromatic nylon. The fiber is strong but small filament size limits it performance for light knit gloves.  The high tensile strength with  small filaments make this a better puncture material than a cut product.  For cut level 4 and 5 gloves we need high density knit fiber cover. These high cover knits are bulky and not very comfortable.  For the Para-Aramid TurtleSkin product there is enough fiber density to provide both cut and puncture. One side benefit of the Para-aramids is they are high temp materials and have excellent flame performance. On the down side Para-Aramids have iffy chemical performance, acids and chlorine bleach are big trouble for these materials.  One last caution, Para-Aramid fibers are not good in abrasion, gloves made from these fibers should have a coating or a cover glove.

Ultra High Molecular Weight Polyethylene UHMWPE

UHMWPE is Spectra and Dyneema fiber significantly stronger than the Para-aramids. They are also small filament yarns with the exception of the new Dyneema Diamond fiber.  Good cut performance and excellent chemical resistance to most common compounds. On the down side these materials can only handle about 220F and start to fail at just slightly higher temperatures. Because UHMWPE is polyethylene it is very low friction. This makes UHMWPE a poor choice for puncture resistance.  In addition UHMWPE will burn and has a bad melt drip issue so all around not a good high temp material.

Liquid Crystal Polyester

The LCP or Vectran material has tensile strength between UHMWPE and Para-Aramid.  LCP is a large denier per filament fiber and has very good cut. Because LCP is Aromatic Polyester it is also a high temp fiber.  LCP fiber is resistant to most industrial chemistry and has some flame resistance. LCP is better all around in abrasion than either Para-Aramid or UHMWPE.  Bear in mid that abrasion and durability in gloves is a complex topic and this review is a summary.   The combination of large filament, tensile, chem resistance, high temp, and abrasion make Vectran a strong competitor. Great combination performance in cut and puncture applications

Fiberglass

Fiberglass is just glass, and as you would expect it is fragile.  Fiberglass does not do well in abrasion or in flex, the damaged surface of fiber glass yarn has sharp ends of broken filament exposed and this shape filament can cause skin irritation.  However fiberglass is very hard when compared to all the organic fibers we have talked about, fiber glass is harder than most cutting tools. The glass fiber breaks down the cutting edge of the threat and and gives good cut resistance.  As long as the fiberglass has a protective cover of one of the other fibers on the list it is a tough high cut fiber. Not a surprise that fiberglass has great thermal resistance and will not burn. Chem resistance is uneven.

Stainless Steel

Like fiberglass stainless steel fiber is a specialty item that is used in combination with one of the other fibers. This fiber has all the properties of steel, hardness, toughness and stiffness. Good thermal and chemical resistance, however as this material is used in a blend these properties are only as useful and the total performance of the blended yarn. To address the stiffness of steel these fibers a low denier per filament and this limits the performance to some degree. The exception is ring mail gloves that over come the stiffness issue with a special welded fabrication process.

 

© 2014 Warwick Mills Inc. All rights reserved.

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The Knit Needs to Work with the Dip (Basics of Dipped Knit Gloves)

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Knit Glove Basics

Knit gloves are made on knitting machines with a limited range of needle density. Thick gloves made from large yarns are generally knit on machines of 8-10 gauge (8-10 needles per inch). These yarns are the same size you find in winter coats. The larger yarns require the larger needle spacing.  Many high cut level gloves  (level 4-5)  use these large yarns and 8-10 gauge knits. For finer and thinner knit gloves the most common knitting style is 13 needles per inch. The 13-gauge knits often use small yarns such as 210 denier nylon. This is about the size of the yarn you use in an oxford shirt.

Openness in Knit Fabric

The knitting machine gauge and the yarn size controls how open the glove textile will be. As an example,  for 13-gauge knits using our 210 denier yarn there is perhaps 30-40% open area in the textile. The % openness in the knit affects how the glove feels and how much stretch it will have. Most users would agree that more open knits result in cooler more comfortable and dexterous gloves.  The down side of more open knits is that it is much harder to create high cut level gloves with small yarns with open space. (More on this in another post.)

The Knit Needs to Work with the Dip

Most users like the grip and durability that palm coated knit gloves offer.   Knit gloves with high levels of openness have an additional benefit for dipping and coating.  With high open area the dip coating can penetrate the textile and encapsulate the yarn on the palm of the glove.  The dip can by nitrile,  polyurethane or NR latex. When the dip can penetrate the knit the coating has the best possible attachment to the textile.  We all want our gloves to be durable and comfortable.  For comfortable gloves with good dexterity the coating and the knit must be thin, no more than 2-4mm in thickness total.  For this type of thin coating layer to be durable it must be well supported by the textile. The rubber in the coating does not have good tear strength. The yarn in the glove provides the reinforcement to prevent premature failure of the coating layer.

When the knit works with the dip you can build a thin comfortable durable glove.

© 2014 Warwick Mills Inc. All rights reserved.

 

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