Nomex Fabric Characteristics

 

    

    The following information is provided as a guideline for evaluating the NOMEX® fabric for the use as a protective garment. Included is what we feel are important characteristics of the NOMEX® fabric in what you may want to consider when selecting the protective apparel for your working environment.
    The following links will take you to more specific information on the subject that pertains to information contained within that link.

 

Nomex Clothing

 

Nomex Applications
Applications that nomex garments are used in from industrial to essential services.

Nomex Fabric Characteristics
The characteristics of the nomex fabric that makes nomex the choice as personal protective apparel for exposure to flash fire and electrical incidents that could cause an arc flash and or blast . 

Cleaning Nomex Fabric
Cleaning of the nomex fabric is really quite simple as the Nomex material can be laundered or dry cleaned.

    

    Nomex is used in a wide range of applications due to the fabric capabilities and thermal properties when there is a possible exposure to a fire source or an electric arc flash. Following are some of the more common Industries and applications that Nomex garments are used in as protective garments
    
    These applications include but are not limited to industrial work wear for:

- petroleum and petrochemical operations
- electricians
- utility workers 
- race car drivers and their crews
- the military
- NASA astronauts and their crews
- medical emergency professionals
- any industry where there is a chance of flash fire exposure or electric arc flash or blast 

    As you can see there are many uses for Nomex garments which are manufactured by various companies into different styles and designs of clothing. Protective clothing is available in coveralls, bib overalls, work shirts, work pants and jackets. The coveralls, bib overalls and jackets are also available as insulated styles for temperatures from mildly cold to extreme cold. 

    The protection provided from Nomex garments gives a person the benefit of a few seconds escape time and the characteristic of Nomex to self extinguish once the person has been removed from the flame source. If the flame source is not removed within a few seconds the fiber will start to char which results in that area not providing any more fuel for the flame in that particular location. 

    The military have been utilizing Nomex garments for many years in the form of personal protection garments when going into combat situations. The assurance that the garment you are wearing will not become part of a fuel source for a flash fire can save a life in certain combat situations.   

    Nomex is usually used either alone or in a blend with Kevlar
® for fire fighters turn out gear and station wear.
Fire fighting crews also utilize a combination of Nomex and Kevlar which provide a thermal protection for contact with a flame source. 
   
Moisture barriers which are incorporated into Nomex fire fighters turn out gear utilize a lightweight blend of Nomex and Kevlar to provide a thermal liner that results in helping to reduce heat stress.

    Nomex suits are very popular in the sport of auto racing as personal protection in the case of accidents on the track or in the pit that may result in a flash fire incident. It is recommended that not only the vehicle driver have the protection of a Nomex garment but also any personal that may in any way become involved in an accidental fire situation.     

    

   The characteristics of Nomex fabric are what makes Nomex a very good choice for the design of flame resistant apparel. The fiber is composed of a synthetic chemical that is in it's self inherently flame resistant. This flame resistant property can not be washed or dry cleaned out of the Nomex fiber and is therefore good for the life of the garment.
   
Nomex will not burn in air like a cotton fabric and will not melt and drip like a polyester fabric. When exposed to a heat source the Nomex fabric will actually expand  form the heat source resulting in establishing a defensive mechanism from the flame source.
    When exposed to a flame source Nomex absorbs the heat energy and the fiber will swell up, thickening in the process which in turn helps to stop heat transfer to the individual person.
    In the case of static electricity which can possibly be a hazard in petroleum plants Nomex IIIA incorporates a static dissipate which attracts static charges to it's carbon core which results in lowering the static charge. Kevlar is also added to the Nomex IIIA to help establish a stronger break open point for the garments. This addition of 5% Kevlar also helps establish Nomex IIIA as having a better abrasive resistant factor and longer garment life compared to FR Cotton fabrics.  

    The physical action of the Nomex fiber when exposed to a heat source such as a flash fire or electric arc is as follows:  

• The fiber itself absorbs heat energy during the carbonization process.

• The fiber swells and thickens in size and seals openings in the garment fabric helping to eliminate air movement and heat transfer to the interior skin area.

• As both the fiber and the fabric thicken together this increases the insulating barrier and therefore reducing heat transfer to the person. 

    Nomex IIIA has a static dissipative added to the fibers that helps control static electricity in certain applications where the presence of even a small electrical discharge could cause an ignition source. The static dissipate that is added to Nomex is P-140 which is a carbon core and insulating sheath. The properties of the P-140 attract static charges from the fabric until the buildup of static electricity ionizes the surrounding air molecules resulting in reducing the charge.
    Nomex IIIA maintains it's static dissipation qualities even in low humidity conditions where 100% cotton fabric may not provide as much anti-static protection. 
This is due to the fact that 100% cotton relies on the absorption of moisture to help eliminate the static buildup. When subject to low humidity conditions cotton will not be able to provide the same protection as the Nomex IIIA due to the loss of moisture. As mentioned above Nomex IIIA has the ability to maintain it's anti static buildup even in low humidity conditions.
    In the construction of flame resistant apparel Kevlar and Nomex are the fabrics of choice. Depending on the application the choice between the two fabrics is one of comfort and protection requirements. Kevlar is much more abrasive resistant then Nomex and is therefore used in a higher concentration percentage of garment fabric design in professional firefighter's turnout gear. Where as Nomex is a softer feeling fiber and is used to a higher degree in daily use garments because of it's greater comfort provided to the wearer. Kevlar is however added to Nomex IIIA to provide a higher degree of strength to the apparel.
    In the the process of adding Kevlar to the Nomex material however there is a decrease in the thermal protection due to the characteristics of the two materials. What happens is that in order to provide a stronger material and a reduced break open point the result is that the material fibers will have a reduced flame shrinkage which in turn makes the fiber stronger but at the same time there is a loss of the barrier material and insulating air layer between the flame source and the wearer, potentially increasing burn injury. Because of this in the case where more protection is required, multiple layers of Nomex IIIA may be required to achieve the desired protection when exposed to electric arc incidents. 

 

Test Methods

    There are five main industry test procedures performed on the Nomex IIIA fabric that conform to certain industry standards that have been developed through the standards organizations involved. In order for a fabric to be accepted to use as a flame resistant material it must pass these tests and therefore conform with the ASTM (American Society for Testing and Materials) and the NFPA (National Fire Protection Association) standards.  
   
    These five tests are as follows:

 

    Vertical Flame Test

    The Vertical Flame Test is the Federal Standard 191A, Method 5903.1 which is a measurement of the flammability of a certain fabric. The fabric being tested is subject to a methane burner flame that is applied to the bottom edge of the fabric for a time period of twelve seconds. The burner flame is then turned off and measurements are taken to determine the char length which is the after flame or amount that a flame continues to burn on the fabric after the flame source is turned off. Also measured is the after glow which is the amount of time that the fabric continues to glow when the after flame stops burning.  
    The Vertical Flame Test is used to measure the flammability of a fabric only and is therefore just one of the tests required when determining the suitability of a flame resistant fabric's capabilities.

Fabric Weight (oz/yd²) Char Length (inches) After Flame (seconds)
Nomex IIIA 4.5 oz 4.5 oz 3.3 0.0
Nomex IIIA 6.1 oz 6.1 oz 3.1 0.0
65%35% Poly/Cotton 8.6 oz 8.6 oz 12.0 48.5
100% Cotton 9.0 oz 9.0 oz 12.0 36.0

* Average of warp and fill determinations. Fabrics were HOME laundered prior to testing. Test utilizes a fabric specimen of 12 inches in length.


    As you can see the polyester cotton blend and the 100% cotton test fabrics continued to burn until the whole sample piece was consumed. This test goes to show what a garment made of these non flame resistant materials will perform like when subject to a flame source. The continuation of a fabric to burn even after it has been removed from the flame source is the main reason that injury and/or fatal disasters can occur to a person wearing these garments. 
The Nomex on the other hand self extinguished within a 3.1 to a 3.3 inch burn length and had no after flame glow.

 

Thermal Protective Performance Test

       The Thermal Protective Performance (TPP) Test is used  for determining the thermal  properties of the fabric being tested. The TPP is recognized in the NFPA 1971 and the ASTM D-4108 as an acceptable measure of a fabric's protection when considering the amount of radiant heat a fabric can withstand
    The Thermal Protective Performance Test is performed by having a convective/radiant heat source with a heat flux of 2 cal/cm
²-sec impinged on the outer surface of a 4-inch by 4-inch area of the fabric. The heat is applied for a specified amount of time in order to reach the equivalent of a second-degree burn at the calorimeter on the other side of the fabric. 
    The test is performed within the confines of a system where one side of the system is in contact with the test fabric, which it's self is in contact with a heat source on the other side of this surface and is heated to the point where
the calorimeter on the opposite side of the fabric reaches an equivalent of a second degree burn. The time (in seconds) which is multiplied by the heat flux of the exposure, gives the Thermal Protective Performance rating of the system. The ratings assigned a given piece of fabric are given a higher TPP value for the higher level of protection a fabric provides.
    There is two test procedures for a TPP, one of which is for single layer garments and the other test is for multilayer garments. When applying the test to a single layer garment there is a 1/4 inch spacer inserted between the heat source plate and the fabric to mimic the space between the garment and the individual person. 
    In the case of a multilayer garment test such as fire fighter turnout gear the sample and heat sensor is in contact with the innermost fabric layer of the system
and there is no spacer is used for a multilayer fabric test resulting in the fabric having to be much more protective in order to pass the test.

.

Single Layer Garment Test Results

Fabric Weight (oz/yd²) TPP cal/cm²
Nomex IIIA 4.5 oz 4.5 oz 11.8
Nomex IIIA 6.1 oz 6.1 oz 13.3
Nomex IIIA 7.5 oz 7.5 oz 15.3

* 2.0 cal/cm2-sec heat flux. Fabrics were HOME laundered one time prior to testing.

 

Multi Layer Garment Test Results

Fabric Fabric Weight oz/yd² cal/cm²
Nomex Omega    
Outer Shell Fabric of Z-200™ fiber at 7.5 oz/yd² 18.8 - 20.5 51.2 - 53.6
Moisture Barrier Breathable PTFE film on NOMEX® E89™ or NOMEX® pajama check  
Thermal Liner

3 layers of NOMEX® E89™ quilted to 2.2 oz/yd² fabric from NOMEX® filament yarn

Nomex with Kevlar    
Outer Shell 60/40 KEVLAR®/NOMEX® blend at 7.0 oz/yd² 18.9 - 20.1 43.7 - 44.8
Moisture Barrier

Breathable PTFE film on NOMEX® E89™ or NOMEX® pajama check

 
Thermal Liner

2 layers of NOMEX® E89™ quilted to 4.4 oz/yd² fabric from NOMEX® spun/filament yarns

Nomex     
Outer Shell NOMEX® IIIA at 7.5 oz/yd² 19.5–19.8 41.0–42.9
Moisture Barrier

Breathable PTFE film on NOMEX® E89™ or NOMEX® pajama check

 
Thermal Liner

Aramid batt quilted to 3.2 oz/yd² fabric from NOMEX® spun yarn

* 2.0 cal/cm2-sec heat flux. Tested as received.

NOMEX® E-89™ is a trademark of E.I. du Pont de Nemours and Company for its spunlaced fabric made from a blend of NOMEX® and KEVLAR® fibers by the SONTARA® spunlace process.
SONTARA® is a registered trademark E.I. du Pont de Nemours and Company.

 

Instrumented Manikin Tests for Flash Fires

 

    This test utilizing Dupont's instrumental manikin THERMO-MAN® uses skin model software in a simulation where a flash fire situation is produced. The software determines a prediction as to the percentage of the 2nd and 3rd degree burns to the body that may be possible in a given flash fire situation. 
    The data collected from these tests can be reproduced to get a more accurate result through continued observation. These tests using THERMO-MAN® and the associated software conform to the ASTM F 1930 standard. 
    Tests conducted show results in comparing the percentage of burn experienced when comparing the 6.1 oz Nomex to 100% cotton fabric and 65% / 35% polyester/cotton blend fabric. The table below shows the results achieved. 

 

  

Fabric Burn Degree Percentage of Body Burn
Nomex IIIA 6.1 oz 2nd and 3rd Degree 35%
100% Cotton 6.5 oz Shirt / 8.5 oz Pant   75% to 90%
Poly/cotton blend 7.5 oz coverall   75% to 90%

A 90% body burn level translates into less than a 30% chance of survival for the 20’s and 30’s age group and less than a 15% chance of survival for the 40’s and 50’s age group.
    In contrast, the chance of survival for a burn injury level of less than 40% of the body is greater than 80% for all age groups.

* Please note that these test results are simulated cases and may differ in results from a real life situation where the exposure to the flash fire is unpredictable..

 

Instrumented Manikin Tests for Electric Arc Exposure

     Testing performed to determine the degree of second degree burns due to an electric arc exposure is performed under very similar conditions as the manikin test procedure as used in the previous flash fire manikin test. The test for arc flash also incorporates copper calorimeters which measure the temperature with the test fabric covering the calorimeters. Human tissue is very relative to the heat that is generated at the test calorimeters and can be used to determine whether a second degree burn may be the result of an electric arc exposure at the arc test point. This manikin test which conforms to ASTM F1959/F 1959M-99 is also used to determine possible results of fabric ignition, fabric melting, shrinkage and brittleness and the amount of fabric weakness that may experienced. The break open point of the fabric also must be tested as to ensure when a fabric gets to the point of such fatigue that the garment physically "breaks open" and can no longer provide a person with the expected protection from an arc flash incident.  

 

Using specific software and/or consultant agencies designed for calculating the incident energy generated from an electric arc the appropriate exposure level can be determined and therefore the corresponding protective measures can be put in place. The calculations take into consideration elements such as the available current at the point of a possible fault, time of the arc (in seconds), arc gap and the distance the person is from the arc source. 
Once the possible exposure levels are determined employers and employees must select the appropriate personal protective equipment to help protect the exposed workers.
The importance of electric arc incidents can not be expressed enough due to the fact that most occurrences of electric arcs are of the "non contact" variety and may be assumed to be non existent. This is a very serious problem as the incident energy a person may be exposed to can be much greater then that of a flash fire.

Listed below are the ATPV (arc thermal performance value) ratings of the Nomex fabrics and their association with the hazard risk categories put out out in the NFPA 70E 2004 (standard for electrical safety in the workplace).

 

Hazard Risk Category Nomex Fabric Compliant Systems Required Minimum Arc Rating of PPE [J/cm²(cal/cm²)]
0 Shirt, pants or coverall 4.5 oz/yd² N/A
1 Shirt, pants or coverall 4.5 oz/yd² 4 cal/cm² or 16.74 J/cm²
2 Shirt, pants or coverall 8.0 oz/yd² Nomex AP 
or 
Non-melting untreated natural fiber under garments plus 4.5 oz/yd² shirt, pants and coverall 4.5 oz/yd²
8 cal/cm² or 33.7 J/cm²
3 Shirt, pants or coverall 4.5 oz/yd² Nomex IIIA plus Jacket consisting of two layers of 7.5 oz/yd2 NOMEX® IIIA.
or 
Non-melting untreated natural fiber under garments plus 4.5 oz/yd² shirt, pants and coverall 4.5 oz/yd²
25 cal/cm² or 104.6 J/cm²
4    

Jacket consisting of two layers of 7.5 oz/yd2 NOMEX® IIIA worn over 100% cotton
knit (4.5 oz/yd2) with insulated bib overalls with a facecloth of 6.0 oz/yd2
NOMEX® IIIA, and a quilted liner consisting of a 7.5 oz/yd2 batt of NOMEX®
quilted to a 3.0 oz/yd2 liner of NOMEX® worn over 100% cotton knit (4.5 oz/yd2)


   

Static charge decay test

    The static charge decay test conforms to Federal Test Standard 191A, Method 5931 which involves the test fabric to be supported between two electrodes then exposed to 5 KV source. Dupont requires that their Nomex IIIA must accept a minimum of 3 KV and be able to discharge 10% of this voltage within ½ of a second at the precise time that the electrodes are grounded. This test procedure is taken place in a controlled environment of 70 degrees F. (21 degrees C.) and 20% relative humidity. 

    In industrial applications where a garment can not be used where there is a chance of the fabric being able to conductive any form of a static electric charge Nomex IIIA has been designed with the addition of the P-140 fiber for static electricity dissipation. The P-140 fiber dissipates static electricity that is generated from fabric to fabric and fabric to surface rubbing and minimizes hazards that may be created by nuisance static electricity.

Following is a comparison chart of the fabric characteristics of Nomex IIIA, Nomex, 100% Cotton and Polyester/ cotton blend fabrics. Please take note of the affect of subsequent launderings to the test fabrics and the degrading factor of static dissipative properties that each fabric experiences.

Fabric Number of Launderings KV Accepted Seconds to discharge 10% of KV accepted
Nomex IIIA  0 3.95 .01
25 3.75 .02
50 3.45 .01
100 3.10 .01
Nomex III 0 4.50 8.9
25 1.35 >10
50 1.35 >10
100 1.35 >10
100% Cotton 0 3.82 >10
25 2.14 >10
50 2.03 >10
65%/35% Polyester/ Cotton Blend 0 4.90 4.3
25 2.20 >10
50 2.25 >10

 

    

     

 

 

 

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