Parity in Protection: What You Should Know About FRC and Static Electricity

What to Consider Before Choosing Industrial Laundry for FRC

Static electricity is a stationary electric charge, typically produced by friction that causes sparks or crackling, or the attraction of dust or hair. Static electricity is named in contrast with current electricity which flows through wires or other conductors and transmits energy (1). Static electricity is an imbalance of electric charges within or on the surface of a material. The charge remains until it is able to move away by means of an electric current or electrical discharge. We are all familiar with the feeling of static shock, caused by the neutralization of such a charge.

Static + FR Clothing

Static electricity on clothing is most often a nuisance in the form of a garment clinging to the wearer’s body. In fact, the main source of spark potential comes from static charges stored in the body of an ungrounded worker rather than from the garments the worker is wearing (2). The ungrounded human body can store energies as high as 40 millijoules while clothing can hold less than 5% of that amount (3).

Some FR fabrics contain a static dissipative fiber which helps dissipate static charges in the fabric. These fibers can reduce the contribution of clothing to the static buildup on the wearer’s body. Even with a static dissipative fiber present, the risk of static cannot be completely removed, and thus workers in high risk environments are recommended to use grounding devices available for this hazard.

The contribution of clothing to static charge buildup is very small as long as wearers do not don or remove items of clothing in a hazardous area. Donning or removing garments can generate static charge on the fabrics through friction and cause charge separation between the layers of clothing. Increased charge on the fabric and charge separation amplifies the likelihood of spark generation from the fabric surface. Therefore, the act of donning or removing garments can increase the charge on the human body and provide a source of spark energy (9). Additionally, people can carry a charge a considerable distance before discharging.

Nuisance Static Tests

AATCC Test Method 76-2011 determines the Electrical Resistivity of Fabrics for nuisance static. The surface electrical resistivity may influence the accumulation of electrostatic charge of a fabric. Fabrics at equilibrium with specified atmospheric conditions of relative humidity and temperature are measured for electrical resistance between parallel electrodes by means of an electrical resistance meter (4).

This test will classify material as:

Insulative – Materials that have a high electrical resistance and are difficult to ground. Static charges will remain in place on these materials for a very long time.

  • Insulative materials have a volume resistivity of greater than 1×10^11 Ohms/cm or surface resistivity greater than 1×10^12 Ohms/sq. (5)

Dissipative – Materials that allow static charges to flow to the ground more slowly in a more controlled manner than with conductive materials. Dissipative materials prevent discharge to or from human contact. While static dissipative fabrics are useful in critical static situations requiring discharge properties, the fabric alone cannot be expected to perform the function of static discharge plates, conductive shoes and flooring/grounding cords (6).

  • Dissipative material has a volume resistivity between 1×10^4Ohms and 1×10^11 Ohms/cm or surface resistivity between 1×10^5 and 1×10^12 Ohms/sq. (6)

Conductive – Materials that have a low electrical resistance and provide a path for static charge to bleed off (7).

  • Conductive materials have no initial charge and a surface resistivity of less than 1×10^5 Ohms/sq or a volume resistivity of less than 1×10^4 Ohms/cm. (6)

FTTS-FA-009 is the standard outlining Specified Requirements of Antistatic Textiles for nuisance static. Its purpose is to test the durability of antistatic properties of textiles (apparel) after repeated washing and weathering. This test determines if the textile is an insulative or static dissipative material then assigns a grade and classification to the material (8).

“Anti-static” materials are generally referred to as any materials that inhibit triboelectric charging (8). The triboelectric effect is a type of contact electrification in which certain materials become electrically charged after they come into contact with another different material through friction. Most everyday static electricity is triboelectric (9).

Parity in Static Control

The generation of static electricity on clothing depends on a number of factors: fabric type, relative humidity, the use of grounding devices and finally, the task being performed. Water conducts and helps distribute a static charge. Therefore, one of the biggest factors affecting static charge is the fabric’s ability to absorb moisture. Moisture content of fabric will help dissipate the static charge more, so that it doesn’t build up. Generally, natural fabrics like cotton retain less static buildup than synthetic fibers, like polyester and nylon, at higher humidity levels (5). Since absorbed water is conducting the charge and not the cotton fiber itself, even cotton fabric is ineffective at dissipating static charges at low levels of relative humidity (6).

The University of Alberta conducted testing on eight sample fabrics for surface resistivity per AATCC Test Method 76. The materials were tested for electrical resistivity at 25%, 50% and 65% relative humidity (RH). The materials were tested in the “as received” (unwashed) condition. The average results of three resistivities, measured in the Log of Ohms per square, are below:

Fabric Tested

25% RH (face/back)

50% RH (face/back)

65% RH (face/back)

Kevlar®/PBI® 4.5 oz.

12.30/12.20

11.10/11.10

10.50/10.60

Nomex®/Rayon 4.5 oz.

13.00/12.90

11.10/11.10

9.80/9.90

Nomex®/Rayon 6.5 oz.

13.20/13.40

11.20/11.40

9.70/9.80

Nomex® IIIA 4.5 oz.

12.90/12.90

11.80/11.90

10.20/10.90

Nomex® IIIA 6.0 oz.

13.00/13.10

12.00/11.90

10.90/11.00

Nomex® IIIA 7.5 oz.

12.90/12.90

11.90/11.70

10.90/10.80

S/301 Indura Ultra Soft® 7.0 oz.

13.30/13.00

11.60/11.30

10.30/10.20

S/451 Indura Ultra Soft® 9.0 oz.

13.10/13.00

11.10/10.80

9.50/9.30

Additionally, Tyndale tested eight sample fabrics for surface resistivity per AATCC Test Method 76. The fabrics were conditioned for 48 hours at 25% relative humidity (RH). The results of this testing are summarized below:

Fabric Tested

Part #

Mean Surface Resistivity (Ohms/sq)

Ultra Soft® 12 oz. Denim U290T-DNM

5.17×1012

Ultra Soft® 12 oz. Fleece U720U

1.34×1011

Ultra Soft® 6 oz. Knit U060T

6.49×1012

100% Cotton NFR Denim C2AEB

1.99×1011

100% Cotton NFR Fleece C7APX

4.82×1012

100% Cotton Work Shirt C1ALB

2.10×1011

FRMC® 14 oz. Denim F290T

7.33×1012

FRMC® 14 oz. Fleece F700T

8.19×1012

As the results of both tests indicate, various flame resistant fabrics result in similar levels of surface resistivity when compared to other FR fabrics, and as Tyndale’s results show, even non-FR fabrics at low RH. While the results show some FR fabrics just slightly on the “insulative” side and others just slightly on the “static dissipative” side, virtually all common FR fabrics require grounding techniques in low RH. These results conclude that none of the tested FR fabrics is better than another, as there is relative parity among many FR fabrics with regard to static.

This conclusion was further confirmed by independent testing conducted at the University of Alberta’s Textile Analysis Services to the AATCC 76 test at 20% humidity. The results of this test indicated the fabrics would not be classed as dissipative at such low humidity levels (10). Therefore, even clothing with dissipative fiber such as Nomex® IIIA is not designed for use in critical static control applications and virtually no FR fabrics are truly anti-static (except some specialty items). (11)

Static in the Oil & Gas Industry

As in high-end technology manufacturing, the danger of static electricity in natural gas distribution has been highlighted over the past few decades. Natural gas explosions have occurred due to the combination of a flammable gas-air mixture and the discharge of static electricity by arcing. Static charge on a plastic pipe can be generated by friction during the physical handling of the pipe in storage, shipping, installation and repairing operations (11). Additionally, fuel and storage tanks, propane gas cylinder processing facilities and fueling operations have been identified as being at risk for fire and explosion caused by static electric discharge (12).

Static electricity that builds up on equipment can create a severe hazard for industries that deal with flammable substances, where a small electrical spark may ignite explosive materials. Identifying static discharge control areas and removing field sources of static are necessary to reduce the risk of static electricity.

Conclusion: Because there is no true “static test” in the United States, it is important to do your hazard assessment and consider the work environment. Finally, proper training and protection remain critical to reducing the risk of static electricity in oil and gas operations since there is no current safety standard for employers to abide by or turn to regarding static hazards for protective clothing.

References for this post were accessed February 2014:

(1) http://en.wikipedia.org/wiki/Static_electricity

(10) INDURA® Ultra Soft® Flame Resistant Fabrics Westex, Inc. Technical Brief

1 Comment

  1. Jörg Vois says:

    Modern flame retardant fabrics are modified with antistatic fibres such as carbone fibres. Nomex(R) Comfort yarns have a Content of 2% Carbone fibres which protects the garment from electric charge.

    Garments, constructed with 100% Nomex(R) Comfort fullfill the EN 1149-3; EN 1149-5.

    We, FUCHSHUBER TECHNO-TEX GmbH, offers a full range of certified products.

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