Infection Control PPE, Textile Evaluation Using Pathogen Contact Transfer Testing

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High Speed Decontamination for Infection Control PPE Applications

New antimicrobial textiles have very fast rates of self decontamination. Chlorine based systems can achieve 99.9% decon in 30 sec with model pathogens.  From the standpoint of Heathcare, users need to know that their PPE textile materials are free of infectious particles. These high speed decon speeds are very helpful for PPE applications.  The contamination state of textiles in infection control PPE affects doffing and disposal behavior. When the textile self-decontaminates in 30 seconds the doffing and disposal processes are lower risk.

Slash Zone PPE Material Testing 

Measurement of textiles for pathogen contamination can be done using various test methods. AATCC Method 100 is the most common test used in the US. There are closely related methods used in Europe and Asia. Method 100 uses a pathogen challenge liquid, applied so it saturates the textile and after hold time. there is a liquid extraction from the textile used to measure the level of self-decontamination. This saturation challenge and liquid extraction assay are appropriate for bedding, wipes, dressings and other textiles used in direct contact with patients and infectious fluids. In infection control PPE, the splash zone materials are impermeable membranes like gloves or membrane textile laminates used in aprons and gowns.

Contact Transfer PPE Materials

In infection control PPE ensembles, there are textile components that are not in the splash zone in patient care and are not subject to saturation by infectious fluids. A good example is an inner glove worn to provide mechanical protection from barrier glove failure. The BioTecT self-decontaminating textile glove is not used in patient contact or exposed to contact with splash risk. In this configuration the contamination risk to the inner BioTecT glove is from pin hole failures in the outer glove or doffing related contamination when the outer gloves are removed. A useful distinction in the infection control PPE ensemble should be made between Splash Zone materials and Contact Transfer Zone materials.

Contact Transfer Zone Material Testing 

In order to evaluate these challenge conditions, a related test was developed which uses a plated liquid pathogen challenge on agar and then after hold time, a contact transfer is made to a second agar plate to measure the level of self-decontamination. Modified Method 100 for Contact Transfer Challenge Test (CTC Test)  is the new test designation. This draft test method is attached to this blog post. This method is much more consistent with the pathogen challenges that Contact Transfer Zone materials are subject to in the PPE ensemble.  Infection control PPE textile layers are used behind a barrier membrane and can be evaluated with the CTC test method. An important aspect of the CTC method is the opportunity to run the assay at speed. Because Contact Challenge and Contact Transfer assay can be preformed in seconds, the rate of self-decon can be evaluated for exposure times to 15-30 seconds. The method 100 assay is limited to exposure times greater than 10 minutes.  Using CTC testing textile contamination state can be evaluated for activities times that include doffing and donning speeds. Knowing that the textile layers in the Infection Control PPE Ensemble have completed their self decon process improves the safety of PPE systems.
If you want to test the high speed self decon BioTecT glove follow the link.
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Infection Control PPE… a Missing Element: Self-Decontaminating Textiles

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Ebola risk has high lighted Infection Control PPE technology
There are currently 3 primary materials used in Infection Control PPE:
  • Barrier membranes (some with and some without textile layers)
  • Filter textiles
  • Basic textiles
  • Missing: Self Decontaminating non-barrier textiles 

Barrier Membranes

The barrier membrane textiles are use naturally to prevent liquids from penetrating the Personnel Protective Equipment (PPE) ensemble. The barriers must be competent to prevent liquids containing viral particles from penetrating. The ASTM 1671 is the most common test criteria for these materials. Under the 1671 criteria the membranes must be capable of preventing viral penetration at 2psi or 54 inches of water pressure. As a result of this rigorous requirement the barrier membranes used in healthcare have limited moisture vapor transport. With low moisture transport from the ensemble the ever present heat stress risk in PPE becomes a serious issue in “Ebola type”  treatment environments. The reason is in high infection risk Ebola treatment we currently have high PPE coverage using barrier textile materials.  Cooler work environments are helpful never the less work sessions wearing high coverage barrier garments must be short, 2 hours or less in many situations. Healthcare workers must move ~150 watts of heat in order to maintain core body temperatures. As barrier membrane coverage area goes up workers in PPE find that they are not able to move there metabolic heat out of the ensemble. CDC and NIOSH are working new standards for Healthcare PPE materials. 

Filter textiles

Filter textiles are well accepted in healthcare, the N95 mask is a good example. This air filter requirement defines a textile that traps 95 of small <1 micron particles in the respiratory air flows. The limit of 95% is based on the need to limit respiratory effort. If the capture rate is higher the filter creates unacceptable restrictions to breathing because of the pressure drop over the filter materials. battery powered air pumps can be used to overcome the pressure drop from higher capacity filters. This down side is these powered full face filter units are not disposable and must be decontaminated manually after each use. The CDC Blog has more details on filter performance and filtration mechanisms 
Basic cotton and poly-cotton textiles are ubiquitous in Healthcare. Scrubs and many other garments are used in PPE, hoods and other articles. Basic textile layers are not considered a key part of the infection control system

Self Decontaminating Textiles In the Infection Control PPE Ensemble

Self-Decontaminating Non-Barrier Textile enable some really important new healthcare PPE solutions. The use of Self-Decon materials improves the thermal transfer of the PPE system. A significant reduction in heat stress can be achieved. The kill speed of the material in decontamination is important. We have now achieved 99.9% pathogen kill in 30 seconds and 99.99% in 90 seconds using a contact transfer test method. So modern Self-Decontaminating textiles can be used as part of the PPE system on high risk services. At the same time reducing the heat load for the healthcare worker.  Like all PPE materials there are limits to the application of Self-Decon Textiles. They should not be used in the splash zone on the front and arms of the ensemble.  Like the N95 mask the Self-Decon material can be used where splash risk is low.   This provides the opportunity to build infection control PPE ensembles that have 50-60% of the area with good moisture vapor transport for lower heat stress. At the same time these materials provides a lower stress garment the safety of healthcare workers are not compromised because the material provides pathogen self-decon in 30 sec.
Take a look at our self-decontaminating gloves for a good introduction to how these textile tools can help solve your infection control challenges.

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Puncture and Cut Gloves: Engineered Composite Materials

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In this post Knit and woven materials are reviewed and compared for protection and dexterity

In the Post“Safety Gloves: Cut and Puncture Resistant Fibers Explained”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.

Puncture and Cut Gloves Textile Options 

 Knits: The fastest growing textile for puncture and cut gloves 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 gloves.  the more of a given fiber type your have under the cutting edge the better the cut glove  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 puncture and cut gloves are sew from woven textiles,  however wovens don’t have much 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 as knits but  they are standouts for cut and puncture performance. The weaving process can product a very dense textile like our TurtleSkin woven.   TurtleSkin  wovens have very high fiber density and deliver cut 5 performance in a very thin package.  Even better TurtleSkin weaves that have no sliding yarns so these weaves have high puncture resistance even to the smallest 28 gauge hypo needles. Puncture and Cut gloves made of TurtleSkin wovens preserve you tactile sense. You can really feel the shape of small object with these gloves because the wovens are so thin.

Coating-Knit-Woven Composites 

In the TurtleSkin line of Puncture and cut gloves we have found that the best marriage that is both comfortable and protective is to use a composite 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 puncture and cut 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 puncture and cut 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 performance of puncture and cut gloves 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. Full dipped puncture and cut gloves are not as comfortable as palm dipped gloves

Summary

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

 

© 2014 Warwick Mills Inc. All rights reserved.

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Safety Gloves: Cut & Puncture Resistant Fibers Explained

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A very common mistake in selecting safety gloves is picking the wrong fiber type.  As you see in each fiber type’s description below, the fibers used in safety gloves are not all created equal. When you are looking for protection and make purchasing decisions for safety gloves, consider the fiber and the coating.  The fiber is one just element of a safety glove’s construction.  After reading this post on fiber, I also suggest taking a look at a separate post on safety glove construction.  It details the glove’s textile construction and how the whole design of a safety glove works.  It is titled: “The  Puncture and Cut Resistant Textiles and Composites”

Polyester Safety Gloves

Polyester material is perhaps the most widely used synthetic fiber.  It is low in cost and available in many sizes and types.  It has moderate tensile strength and low cut performance, which limits the protection when is used alone.  Polyester yarn is available as a textured yarn.  In this form, it has quite good abrasion for its price point.  Polyester has broad chemical resistance.  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.  Polyester, called PET for short, is used in most of the light weight, palm dipped safety gloves.

Nylon Safety Gloves

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 safety 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 safety 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. Nylon’s chemical resistance is lower than polyester. Like PET, nylon is used extensively in light weight palm dipped safety gloves.

Para-Aramid Safety Gloves

Ball-and-stick model of a single layer of the crystal structure

Para Aramid structure showing the carbon rings connected by nylon linkages

This is the old stand by Kevlar.  The same material, para-aramid also is available under  brand names  Twaron and Technora. Chemically all these fibers are aromatic nylon.  From the image above, notice the hexagonal carbon rings connected into long chains by nylon.  The aromatic carbon rings make these fiber strong. However para aramid yarn must have small filament size. Small filaments have poor abrasion and this  limits it performance for light knit safety gloves.  The high tensile strength with small filaments make this fiber 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.  Cost is a consideration for Para-Aramid fiber as well these yarns are 5-8 times the cost of nylon or polyester. Many safety glove producers blend Para-Aramid with outer lower cost fibers to control cost.  The gloves become some what bulky above level 3 and these is more of an issue as the lower cut fibers are blended in for for cost control. 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, because Para-Aramid fibers have low abrasion, safety gloves made from these fibers should have a coating or a cover glove. Ultra High Molecular Weight Polyethylene UHMWPE Safety Gloves

UHMWPE is a common fiber used in safety gloves

UHMPE is very strong and chemically resistant but does not tolerate high temperatures

UHMWPE (PE) 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 PE is polyethylene it is very low friction. This makes PE a poor choice for puncture resistance.  In addition PE will burn and has a bad melt drip issue so all around not a good high temp material. Many users prefer PE knits to Para-Aramids knit gloves. The PE fiber is slippery and this appears to help a knit safety glove stretch and move to accommodate the users hand.  Many cut level 3-5 safety gloves are build of PE fiber. Like the Para-Aramids, UHMWPE bulk is an issue for designs of knit safety gloves, particularly above level 3. Liquid Crystal Polyester  Safety Gloves

 High end safety gloves are produced from LCP yarns

LCP yarn has high strength and large filaments resulting in excellent cut and abrasion.

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 safety 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. Given the higher cost of LCP, almost all safety gloves use this material blended with lower cost fiber.

Fiberglass in Safety Gloves 

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.  Fiberglass yarn can help make a high performance safety glove. The fiberglass needs  a protective cover of one of the other fibers on the list to protect the more brittle glass fiber.   Not a surprise that fiberglass has great thermal resistance and will not burn safety gloves with ratings up to 2000f can be build with fiberglass yarn. Chemical resistance of fiberglass is uneven.

Stainless Steel in Safety Gloves 

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 overcome the stiffness issue with a special welded fabrication process. Stainless is difficult to work with in textile constructions and this results in high costs for filament stainless yarn  or welded ring male materials.   © 2014 Warwick Mills Inc. All rights reserved.

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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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Cut Glove Optimization: Knit Needs to Work with the Dip

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Knit Basics for Cut Gloves

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. Larger yarns contain more fiber and offer more cut resistance for a cut glove.

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 level cut glove with small yarns with open space. (More on this in another post.)

The Knit Needs to Work with the Dip for Best Cut Glove Dexterity and Cut

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.  A special kind of glove coating uses dots or pads of coating that are thicker than a full dip layer. This dotted coating provides the option to increase the coating thickness and wear resistance without making a cut glove stiff.

For optimal cut glove design the knit density and the coating work together to give you good dexterity and good cut performance.

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

© 2014 Warwick Mills Inc. All rights reserved.

 

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