Lori Hyllengren is the laboratory manager for Red Wing Shoe Co. and S.B. Foot Tanning Co. She has vast experience in product quality testing of leather, footwear and PPE garments across international standards including ASTM, Canadian Standards Association (CSA) and European Standards (EN). Visit redwingshoes.com.
The Occupational Safety and Health Administration (OSHA) reports slips, trips and falls comprise nearly 25 percent of all reported accident claims, including roughly 12,000 accidental deaths every year in the United States.
Employers are placed in a difficult position. While slips, trips and falls are among the most reported and costly injuries, confusion surrounds the definition of slip resistance as well as the accepted method for evaluating slip-resistant footwear.
Purchasing a pair of slip-resistant work boots isn’t as easy as a trip to the shoe store. Unlike other protective aspects of safety footwear, such as toe protection or puncture resistance, slip resistance requirements do not exist in North America. There are a variety of methods for testing slip resistance, and there are guidelines that manufacturers can choose to follow during product testing. Still, neither OSHA, HSE or any other U.S. regulatory body with enforcement power defines or quantifies the slip resistance of footwear.
Prior to 2011, ASTM F-1677 was the common method for testing the slip resistance of footwear. This was known as the Mark II or Brungraber test (named after Dr. Robert Brungraber at Bucknell University, who pioneered the method). However, it was dropped by ASTM more than a decade ago and is no longer supported.
Now, the most relevant testing standard is ASTM F2913, “Standard Test Method for Measuring the Coefficient of Friction for Evaluation of Slip Performance of Footwear and Test Surfaces/Flooring Using a Whole Shoe Tester” (whole shoe test). The whole shoe test is applicable to a variety of footwear materials and test surfaces, including those that are contaminated with slippery substances. As such, it offers a comprehensive picture of a shoe’s slip resistance.
Still, the slip resistance measurement does not guarantee you won’t slip, trip or fall. While it is possible to measure the coefficient of friction of a shoe, slipping involves other variables to consider when choosing proper safety footwear. For example, one shoe may provide adequate slip resistance on dry concrete but become slippery on wet steel. Another may offer substantial slip resistance initially, but if the outsole is not durable and wears down quickly, the slip resistance may diminish.
For construction business owners, it is important to understand the trade-offs versus safety when making a solid assessment of slip resistance for your employees’ footwear.
The first consideration is cost. The least expensive safety footwear may not offer adequate slip resistance for the job. The slip resistance of any footwear comes down to the integration of several anti-slip features, all of which may affect the purchase price. Antiquated technology, uncontrolled manufacturing or low-quality materials could compromise any of these features as well as create durability issues.
Next is comfort. Discomfort can be a distraction to a construction worker, so a proper balance between safety and comfort is necessary. If work boots do not fit properly, employees may look for excuses to avoid wearing them altogether.
Third is overdesign. Surprisingly, it is possible for safety footwear to be too slip resistant. For example, if the boot sticks to a work surface, the wearer runs the risk of injuries like those experienced by athletes who get hurt when cleats stick in the turf.
The ideal situation is to work with a safety footwear provider who can help you to understand benefits versus tradeoffs and assist you in finding the appropriate solution for a specific job environment. There are also a few general guidelines to consider when selecting the right slip resistance features.
Slip resistance performance may change over time as footwear is subjected to normal wear and tear. Employers should prioritize highly durable footwear that provides the most slip resistance for the longest period of time so their workforces can operate with confidence.
Outsole & Tread
The outsole compound is critical for slip resistance. In general, soft rubber compounds offer the greatest slip resistance for work environments contaminated with oil and grease. However, it is important to keep in mind that small changes in the compound can result in large variations in overall slip resistance. Look for outsoles that channel oil, grease and water away so the outsole makes contact with the work surface more fully, as well as outsoles with split and solid lugs that are specifically designed to shed debris.
Treads should allow a maximum amount of material to grip the floor. Softer soles and more tightly spaced treads are better suited to fluid contaminants and indoor environments. More widely spaced treads are generally better for handling solid contaminants in outdoor areas. It is vital to avoid clogging the tread. A wider or deeper tread pattern may be necessary if footwear needs to be cleaned too often. Watch for worn or flattened soles after substantial use, which reduce slip resistance.
Midsoles & Insoles
The midsole should provide ample support and stability. Again, midsole technologies do not have a direct bearing on slip resistance, but they are important for overall structural integrity and the amount of comfort employees can expect. Insoles do not play a direct role in slip resistance, but they should offer additional cushioning and impact padding for employees who are on their feet for extended periods or who work predominantly on hard surfaces.
Uppers can be made of a long list of materials, including various leathers, suede, mesh or a combination. Like insoles, uppers do not directly determine slip resistance but instead play a key role in fit and comfort. A shafted boot (6 or 8 inches tall) offers more ankle stability than a shorter boot such as an oxford.
3 Simple Principles
Because there is no uniform standard or rating for slip resistance, any footwear manufacturer can claim slip resistance. This does not make purchasing safety footwear for your construction crew easy. The best approach is to follow these simple principles.
- Follow ASTM F2913—This standard method (whole shoe test) provides the most complete approach to evaluating how different footwear materials interact with various work surfaces. All slip-resistant footwear should be tested to this standard to establish a common basis for comparison. Again, the Mark II test has been withdrawn by ASTM and should not be used to evaluate safety footwear.
- Understand the details—Whether a specific shoe or boot will provide adequate, long-term slip resistance requires a deep understanding of what the job involves: the surfaces, contaminants and physical requirements of the role. Make sure to take all of this into account when selecting footwear. Your footwear provider should not be giving you something generic, but rather purpose-built safety footwear that adheres to your specific needs.
- Share knowledge—Every work environment is unique. Ensuring slip resistance depends on a strong, open and transparent collaboration between the employer and the safety footwear provider. The footwear manufacturer should not only provide as much detail as possible about its products, but also should seek to understand every nuance of the work environment before making a recommendation.