Protective Footwear Characteristics & Requirements

Developing innovative products that combine comfort with protection would go a long way to reducing the number of workplace accidents.

SHOE BODY

Outer Cover – Membrane

Leather is commonly used for shoe covering, most notably for its mechanical properties. Yet protective shoes are worn continuously for long periods, generating humidity that causes considerable discomfort to the user. New “breathable” membranes2 are starting to appear that drain sweat to the outside more effectively. Microporous membranes, such as Gore-Tex® or HigH2Out® by Sympatex, offer both waterproofness and optimal humidity management. Some shoe manufacturers even offer their own humidity optimizing technology. Chip-A-Tex™ by Chippewa, KEEN.Dry™ by Keen, Hyper-Dri™ by Lacrosse and Dry-W™ by Red Wing are a few examples.

Inner Liner and Padding

Before the humidity can reach the outer surface, it must first cross the shoe’s inner liner and padding. The lining will therefore be made from absorbent capillary-active material, often in microfiber form (e.g. Mark’s Driwear® technology). Honeywell3 has opted for natural bamboo fibers for humidity absorption with its new product Healthtech®. Some companies, such as PowerFootwear’s Dri-Lex® products, incorporate antibacterial agents to inhibit odor formation in the shoe. Finally, a new generation of 3D textiles, such as Honeywell’s Poromax®, is also finding a wider audience because of their superior comfort and optimal shoe ventilation and aeration.

Sizes and Shapes

For many years, the shoe size chart was based on measuring foot length and width—variables now inadequate for defining a shoe style and shape properly adapted to the foot. Some manufacturers are now beginning to incorporate the angular position of the foot sole, and toe length, offering a range of different shoes for each foot size.

Protective Toe Caps

With their mechanical protection against crushing hazards, toe caps have long been made from metal, primarily stainless steel. For the sake of user comfort, new aluminum toe caps have been produced to reduce added weight to the shoe. Manufacturers are now focusing on composite toe caps, often based on polycarbonate and carbon fibers, as reinforcement. These are even lighter and have a much weaker thermal conductivity than metal toe caps—no small advantage in a cold climate.

Inner Sole

These are often manufactured from polyurethane (PU) or thermoplastic polyurethane (TPU). Polymer is often injected directly into the shoe for better cohesion between the sole’s various components, a procedure that is nonetheless restrictive because the sole cannot be made from a single polymer. New production methods now enable soles to be made from four different polymers depending on the areas of the foot under strain. Foam inserts are also incorporated in the insole to provide better shock absorption. Examples are Poron® technology; AirFeet® which incorporates massage areas to maximize comfort; and MEGAS Soles® by MEGA Comfort. Their designs, specially approved by chiropodists, reduce the user’s sensation of fatigue in the joints (knees, hips, etc.) and back.

Insoles are also designed to provide proper ventilation inside the shoe. Perforations are made in the upper part of the sole, as illustrated by Meramec’s Ultron®.

Intermediate Sole

Intermediate soles have thermal insulation properties and offer the greatest protection against punctures. For years, these components were made from metal to stand up to mechanical constraints, but new aramid and polyurethane soles have been developed to address weight and flexibility problems.

For thermal needs, Thinsulate® is widely used commercially. Other technologies, such as Heat Trapolator® by Keen, have similar properties.

Outsole

The outsole is one of the shoe’s most complex elements because it must meet different criteria, including abrasion resistance, anti-slippage, electric shock resistance,  emperature resistance, and more. Rubber is primarily used4 to make this part of the shoe, although products with EVA (Ethylene – Vinyl Acetate) soles are also occasionally found on the market. EVA soles are more flexible than rubber soles, but generally have less mechanical resistance. Soles in Vibram® rubber are an example of the high-performance products currently available in protective shoes. In certain specific cases—if there is a risk of the sole coming in contact with high-temperature areas, for instance—Nitrile may also be necessary.

PROTECTIVE FOOTWEAR REQUIREMENTS

According to the U.S National Safety Council (NSC)5, every year, over 200,000 workers suffer injuries to their feet. Most of these accidents are caused by either trips and same-surface falls, or situations of impact to the top of the foot or toes. The most common injuries are sprains and bruises, but these can lead to work stoppages of four to seven days, depending on the profession, which represent a major loss for companies. The Code of Federal Regulation: 29 CFR 1910-136 established by OSHA6 (Occupational Safety and Health Administration) ensures proper compliance of the protective footwear provided to workers—carpenters, electricians, mechanics and others—to protect them from the hazards of their trade.

Standards in Force

For nearly 60 years, the ANSI Z41-1999 standard was the reference in protective footwear. Since 20057, the ANSI Z41 decision-making committee has been merged with the ASTM F13 committee on protective equipment, giving rise to two new standards: ASTM F2412 and ASTM F2413. These two standards describe, respectively, the test methods for, and performance requirements of,protective footwear. 

  • ASTM F2412 provides detailed testing procedures for evaluating protective footwear. 
  • ASTM F24138 states the minimum requirements for safety footwear based on the tests prescribed in ASTM F2412. ASTM F2413 has two sections. The first part covers two mechanical tests (impact and compression resistance) that are mandatory for a shoe to be certified compliant. The second part of the standard offers additional tests according to profession and the hazards the worker is exposed to. The ASTM F28929 standard is also available in cases where the worker requires protective footwear against specific hazards (electricity, puncture, etc.), but no mechanical protection against impact and compression. In these cases, footwear is considered soft toe due to the lack of  einforcement at the toes. 
  • Up until 2005, tests for dielectric resistance (F1117) and chainsaw cut resistance (F1818) were grouped under standards F2412 and F2413. These have since been withdrawn from the prescribed tests and are now covered by their own standards. 
  • Standards ASTM F609 and ASTM F2913 evaluate slip resistance of safety shoe soles, based on a measurement of the coefficient of friction (COF). 

Properties Evaluated and Test Methods

Impact resistance: The impact resistance test is characterized by the reduction in the height of the toe area of footwear where there is reinforcement.

Impact is applied with a force of 75 ft-lbf. After the test, the height of the shoe must be at least 0.50 inches10 for a men’s shoe for the test to be validated.

Compression resistance: In the case of the compression test, the part of the shoe protecting the toes is subjected to a pressure increasing at a rate of 50 lbf/s until it reaches a maximum of 2500 lbs. Similar to the impact resistance test, the inner height of the shoe is measured according to the same criteria, namely, a minimum of 0.50 inches for a men’s shoe.

Metatarsal impact resistance: This impact resistance test is identical to the one performed on the toe part. The only difference is the position of the point of impact, which is higher up on the shoe—exactly 3.5 inches from the toe end of the shoe for a man. The force of impact here again is 75 ft-lbf, but acceptance criteria are higher, with a minimum height of 1.0 inches.

Puncture resistance: A shoe’s puncture resistance is determined using an intermediate sole placed between the outsole and the insole. This component must first be tested separately from the rest of the shoe to verify its resistance to flexing according to the testing procedure described in the CAN/CSA Z195 standard. A minimum of 1.5 million flexes must be performed without noticeable delamination or cracking. If the intermediate sole is of metal, a corrosion resistance test will also be performed in accordance with the ASTM B117 standard. Finally, the puncture test involves pressing a steel point into the outsole at a constant speed of 0.393 inches per minute until it reaches a force of at least 270 lbf or the insole is punctured. Visual examination of the insole will determine if there is a puncture or not. Mechanical protection is one thing, but footwear must also offer adequate protection in cases where the worker is exposed to electrical hazards. 

Electrical conductivity: The shoe is placed on a stainless steel plate, which constitutes the first electrode. The second electrode is inserted into a metal sphere and placed inside the shoe. A 500 V current flows through a resistance of 100,000 Ω and through the shoe for 30 seconds, during which time the value of the shoe’s electrical resistance is reported. It must be at a maximum of 500,000 Ω to validate the test.

Electric shock resistance: An electrode device made from a metal plate and spheres placed inside the shoe is also used in this test. Increasing voltage is applied between the two electrodes at a rate of 1000 volts per second until it reaches 18,000 volts at a frequency of 60 Hz for one minute. No flow or leakage of current higher than 1.0 mA in dry test conditions must be detected.

Static charge dissipation: The test for static charge dissipation consists in placing a human subject on a stainless steel plate and measuring the current flowing through his body when his hand comes in contact with a metal bar. The metal bar is itself subjected to 50 volts and has a reference protective electrical resistance of 1 megohm. The resistance deducted from the current measured through the individual’s body must be higher than 1 megohm, but lower than 100 megohms.

Slip resistance: Though they are not part of the ASTM F2413 standard, there are also test methods for slip resistance, which come under the F609 and F2913 standards.

In F609’s case, a portable tribometer, such as the Brungraber Mark II, is required. Though widely used, this category of device has many limitations, including the wide variation in results between types of devices. It is also recommended that it be tested beforehand according to the ASTM F2508 standard in order to verify and calibrate the equipment. Furthermore, the sample representing the sole is small in terms of surface and is a relatively uniform structure, which is rarely the case with safety footwear, whose rear studs are often more marked.

The ASTM F2913 standard refers to a complete test bench that evaluates the entire shoe sole. The equipment was initially developed by the British research centre SATRA in the 1970s.

The test takes into account friction at the heel and toes and of the flat shoe on two types of surface: ceramic and steel. Though more complex and comprehensive, this test method still fails to define a minimum COF value because numerous other factors come into play in the slip phenomenon. The results, moreover, can only be used in a comparative study of footwear tested on the same equipment, as values from different devices are not always reliable.

Research is ongoing into how to measure this phenomenon more objectively.

Labelling and Logo

The label certifying footwear compliance must be printed or sewn on both shoes. The logo has three lines. The first line states the number and version of the standard used to test the shoe. The second line indicates who the shoe is designed for (M: male – F: emale) and its impact resistance (I/75) and compression resistance (C/75), the two minimum tests required to meet the ASTM F2413 standard. The third line is used to denote additional properties tested: EH for electrical shocks resistance,

PR for puncture resistance, etc. (Source: ASTM F2413)

Paradoxically, no testing method specific to protective shoes is available to evaluate user comfort, for considerations such as shock absorption, nonirritability, thermal comfort, flexibility or breathability, even though these are the features that manufacturers optimize and promote. In this respect, the American Podiatric Medical Association (APMA) has established a “Comfortable Safety Footwear” certification system, while SATRA has developed a “Comfort Index” that defines a shoe’s overall comfort level based on a series of tests that include pressure distribution tests, thermography and more.

IN CONCLUSION

The industry is demonstrating its commitment to innovation, improving the comfort of protective shoes and, in so doing, making them more popular in the workplace. Users today can choose from a multitude of products offering all kinds of advantages.

In the absence of a standard to evaluate products’ overall comfort/ safety ratio, choosing the right pair can be difficult.

The main elements11 to remember when buying a pair of safety shoes are, first, to properly know the work environment and the risks that come with it. Next, when trying on the shoes, it is essential that they be at least as thick as those worn every day at work. Moreover, once they are laced, the user must be able to move his toes freely and feel comfortable right away because there is no adjustment period for protective footwear. Ideally, it is also a good idea to find a hard, uncarpeted surface in the store to walk on in order to properly evaluate stability and shock absorption. Last, but not least, don’t forget to inspect protective shoes on a regular basis, especially the outsole to check the studs’ degree of wear.

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2. SIKA Footwear. “Technical Terms.” Available at http://www.sika-footwear.dk/. Consulted July 10, 2014.

3. Honeywell. “Safety Footwear.” Available at www.honeywellsafety.com. Consulted July 10, 2014.

4. Safety Footwear International. 2014. “Finding The Best Work Shoes for Your Requirements.”

    Available at http://specialtyfootwearinternational. com/. Consulted July 10, 2014.

5. A . Amendola, H. Hsiao, J. Powers, C. Pan. 2010. “NIOSH strategic goals to reduce fall injuries

    in the workplace.” U.S. Department of Health and Human Services. National Institute for

    Occupational Safety and Health. 255 pages.

6. Occupational Safety and Health Administration. Available at www.osha.gov. Consulted July 9, 2014.

7. W. Ells. 2005. “New ASTM International Standards supersede ANSI Z41 Protective Footwear

    Standards.” ASTM International News Release (#7115).

8. A STM International. 2011. “Standard Specification for Performance Requirements for

    Protective (Safety) Toe Cap Footwear.” ASTM International, ed. West Conshohocken, Pennsylvania. 5 pages.

9. A STM International. 2011. “Standard Specification for Soft Toe Protective Footwear

    (Non-safety / Non-protective toe). ” ASTM International. West Conshohocken, PA. 4 pages.

10. A STM International. 2011. “Standard Test Methods for Foot Protection,” ASTM international.

     West Conshohocken, PA. 17 pages.

11. www.aofas.org/footcaremd/how-to/footwear/ Pages/10-Points-for-Purchasing-Protective- Footwear.aspx