EH Footwear vs. SD Footwear
Here at e-Hazard, we are often asked about Electrical Hazard (EH) footwear versus Static Dissipative (SD) footwear. What type of work shoe or boot is appropriate? Can a qualified electrical worker wear SD footwear while performing testing in an energized electrical panel? What are the ratings of EH versus SD?
What follows below is a quick and dirty version of ASTM F2413 specifications on both types of shoes. We’ll start by including another electrical category that appears in ASTM F2413 – the conductive footwear category (Cd). Here are the electrical summaries of each type, listed in order of appearance in the standard:
Conductive Footwear (Cd):
- Maximum 500,000 ohms of resistance
- The shoe must dissipate static charge
- The shoe must provide a stable electrically-conductive path
- The resistance must be between 0 and 500,000 ohms
Electrical Hazard Footwear (EH):
- Must be capable of withstanding 18,000 volts at 60 hertz for one minute and have a maximum leakage current of 1.0 milliamperes. This is a test parameter for new EH footwear and not intended to be an operating limit after the footwear is placed in service.
Static Dissipative Footwear (SD):
- Must provide protection through conduction and resistance due to “excessively low resistance” as well as “maintain a sufficiently high level of resistance to reduce the possibility of electrical shock” where SD footwear is needed.
- SD Footwear has three categories:
- SD 100 – lower limit of 1 megaohm resistance and an upper limit of 100 megaohms
- SD 35 – lower limit of 1 megaohm resistance and an upper limit of 35 megaohms.
- SD 10 – lower limit of 1 megaohm resistance and an upper limit of 10 megaohms.
So, there we have it – three options for three different applications. Conductive footwear is typically used in areas near volatile compounds, and the ASTM standard warns specifically against using conductive footwear near “open electrical circuits.”
SD footwear is typically used in areas where static discharge is a must, typically in electronics manufacturing or at industrial sites where sensitive electronics are installed/removed, as in computer circuit boards, process logic computers (PLCs), and similar areas. These areas require SD footwear to ensure static buildup from walking is discharged continuously, ensuring safety of the electronic components, while offering at least 1 megaohm to ground for a somewhat small margin of electrical safety. These shoes are NOT recommended for energized electrical work.
A serious concern with SD footwear appears in the ASTM F2413-17 informative note that states, “The inconsistency of certain hygroscopic materials can result in footwear not being able to consistently meet the performance requirements of static dissipative footwear.” As a serious precaution, electrical safety procedures may want to disallow SD footwear for any electrical activities that could create a shock or electrocution hazard.
EH footwear – now THIS is what the same electrical safety procedure mentioned above should require for every electrically-qualified or electrically-task-qualified worker. These shoes are required, as stated above, to exhibit a measured current flow of less than 1 milliamp at 18,000 volts, and up to a full minute of exposure when new. Most shock events are nowhere close to a full minute of exposure.
We recommend wearing EH footwear for exposures up to 1000 volts. Beyond this, Dielectric footwear is recommended within its limits.
Be careful, of course, with EH shoes because, unlike electrically-rated rubber gloves that require voltage testing every 6 months, EH shoes require no such retest once the boots are on the ground. The user needs to follow manufacturer instructions on these shoes, which typically include pre-use inspection for conditions like sole cracking, soles wearing thin, visible damage, etc.
A serious note also appears in the ASTM F2413 standard for EH shoes:
NOTE 3—Electrical hazard protection is severely deteriorated in the following conditions: excessive wear on the soling material, contamination by conductive materials, or exposure to wet environments. In wet environments where the protective qualities of the footwear are compromised and where there is a step potential hazard, Dielectric overshoes should be used. In addition, a variety of methods such as maintaining appropriate distances, use of isolation methods, use of grounding methods for step voltage control, etc. should be considered to provide protection.
All EH shoe/boot wearers should take this note to heart, especially when outside in wet conditions and in areas of step-potential. Dielectric (DI) footwear (covered in ASTM F1117-03) is required in these situations.
Looking at NFPA 70E®
If you want to look at standards and regulations, please refer to NFPA 70E® Article 130.7(C)(8), which specifies DI footwear for protection against step and touch potential. The informational note following this section refers the reader to ASTM F2413 as a SECONDARY source of electrical shock protection under dry conditions.
What Does OSHA Say?
OSHA is a bit more vague in the footwear department, stating in OSHA 1910.136(a) that the employer “shall ensure that each affected employee uses protective footwear when working in areas where there is a danger of foot injuries due to falling or rolling objects, or objects piercing the sole, or when the use of protective footwear will protect the affected employee from an electrical hazard, such as a static-discharge or electric-shock hazard, that remains after the employer takes other necessary protective measures.”
OSHA provides a guide to small businesses that states the following (be aware that this is a 2004 document):
“Electrical hazard, safety-toe shoes are nonconductive and will prevent the wearers’ feet from completing an electrical circuit to the ground. These shoes can protect against open circuits of up to 600 volts in dry conditions and should be used in conjunction with other insulating equipment and additional precautions to reduce the risk of an employee becoming a path for hazardous electrical energy. The insulating protection of electrical hazard, safety-toe shoes may be compromised if the shoes become wet, the soles are worn through, metal particles become embedded in the sole or heel, or employees touch conductive, grounded items. Note: Nonconductive footwear must not be used in explosive or hazardous locations.”
Finally, OSHA mentions DI footwear in Appendix G of 1910.269, referencing ASTM F1116-03 (2008) as the test method specifications for Dielectric Footwear, although a specific requirement is not mentioned in 1910.269 whatsoever.
Know the Purpose of Your Footwear
Remember the purpose of each shoe or work boot and be sure to dress appropriately from head to toe. Employers are ultimately responsible as to what PPE is required for electrical workers, and this should be addressed directly in the company’s electrical safety policy.