It consists of a flashover of electric current that leaves its intended path and travels through the air from one conductor to another or to the ground. While the flash itself is immediate, these incidents can result in long-term medical and financial problems.
According to statistics compiled by CapSchell, Inc., a Chicago-based research and consulting firm that specializes in preventing workplace injuries and deaths, five to ten arc explosions occur in electric equipment every day in the United States, and more than 2,000 people annually are treated in burn centers for severe arc flash injuries. Moreover, the National Safety Council estimates work-related injuries can cost businesses well over $30M in fines, medical costs, litigation, lost business, and equipment costs.
Most often, when there is an arc flash hazard there is also a shock hazard, so dielectric protection is an important component of personal protective equipment when working on or near energized lines and equipment.
Even though a wealth of information exists regarding arc- and flame-resistant clothing requirements, there remains some uncertainty among end users concerning hand protection requirements. Fortunately, there are safety products and procedures that can help protect workers against arc flash and shock when used and followed correctly. Here are five things you can do to ensure you use your rubber insulating products the way they’re meant to be.
Step 1: Dress for Safety!
For line workers, being dressed for safety is more than fashionable – it’s a life saver.
Rubber insulating products such as gloves, blankets, sleeves, line hoses and hoods used by electrical workers today are manufactured in accordance with industry consensus specifications under the auspices of the American Society for Testing and Materials (ASTM). These ASTM standard specifications are referenced in the OSHA regulations dealing with electrical safety, specifically 29CFR1910.137 (covering Electrical Protective Devices), and 29CFR1910.269 (covering Electric Power Generation, Transmission and Distribution).
Bear in mind that rubber gloves are the only protective gear designed for constant contact with, and protection from, energized conductors and equipment. All of the other items are only designed for protection from accidental, incidental, or brush contact.
Choosing the Right Glove
Take care to choose the correct rubber insulating glove for the task at hand and level of electrical exposure. Rubber insulating gloves are typically manufactured in sizes 8-12, often in half sizes, and some manufacturers also offer gloves as small as size 7 and as large as size 13. In addition, rubber insulating gloves are available in different cuff lengths of 11, 14, 16 and 18 inches depending on the glove class.
Rubber insulating gloves are available in six specific voltage classes (Class 00 – Class 4), and other rubber insulating products are available in different voltage classes as well.
Proof Test Voltage
AC / DC
|Max. Use Voltage
AC / DC
|2,500 / 10,000||500 / 750|
|5,000 / 20,000||1,000 / 1,500|
|10,000 / 40,000||7,500 / 11,250|
|20,000 / 50,000||17,000 / 25,500|
|30,000 / 60,000||26,500 / 39,750|
|40,000 / 70,000||
36,000 / 54,000
- Class 00 low voltage gloves are proof-tested at 2,500 volts for a maximum use 500 volts
- Class 0 low voltage gloves are proof-tested at 5,000 volts for a maximum use 1,000 volts
- Class 1 high voltage gloves are proof-tested at 10,000 volts for a maximum use 7,500 volts
- Class 2 high voltage gloves are proof-tested at 20,000 volts for a maximum use 17,000 volts
- Class 3 high voltage gloves are proof-tested at 30,000 volts for a maximum use 26,500 volts
- Class 4 high voltage gloves are proof-tested at 40,000 volts for a maximum use 36,000 volts
These are all AC voltages. The ASTM standards also include DC test and maximum use voltages.
There is a significant margin of safety between the proof-test voltages and the maximum working voltage. Gloves and other rubber insulating products must be permanently marked to indicate the voltage class, and the gloves and sleeves must also have a color-coded label identifying the voltage class.
Choosing Leather Protector Gloves
Equal care and consideration should also be given when selecting the appropriate leather protector gloves.
Leather protector gloves are worn over rubber insulating gloves to extend their life and protect the gloves from cuts, abrasions, and punctures.
Use the ASTM F696 standard specifying the types of materials, construction, and other details as a guide in the selection process. Keep in mind that there is a tracking and flashover risk which increases as the voltage potential increases. Since the materials in the leather protector gloves have no dielectric properties and may absorb moisture (or at least track electricity), it is important to maintain an interval between the leather protector glove and the wearer’s body parts, i.e. hand and arm. Therefore, the leather protector must be shorter than the rubber glove so that there is exposed rubber as a line of defense against tracking and flashover. The applicable ASTM specifications state that the minimum distance between the edge of the leather protector and the cuff edge of the rubber insulating glove is ½ inch for low-voltage gloves and 1 inch per glove class for high-voltage gloves. Knowing this, the leather protector for a Class 2 rubber glove must be at least 2 inches shorter than the rubber glove.
Step 2: Use the ASTM Standard Specification for In-Service Care
Various ASTM Manufacturing and Acceptance standards mandate the testing of the rubber insulating products by the manufacturer or supplier prior to the first delivery to the end user.
Users also have the option of performing or requiring an acceptance test upon receipt of the goods and prior to placing rubber insulating products into service.
Once placed in service, there are periodic re-test intervals specified in the following ASTM standards:
- ASTM F496-08 Rubber Insulating Gloves – 6 months (under certain conditions, this can increase to 9 months)
- ASTM F496-08 Rubber Insulating Sleeves – 12 months
- ASTM F479-06 Rubber Insulating Blankets – 12 months
- ASTM F478-09 Line Hose and Covers – when field inspection or company policy warrant
These in-service re-test intervals are the maximum permitted and they should be performed in addition to daily field care and inspection. It is quite common for users, including power utilities and contractors, to specify shorter intervals.
Damage to many types of PPE is apparent to the user when they inspect the equipment, but rubber electrical insulating products are more complicated. A number of factors could reduce their effectiveness without being noticeable to the user, including:
- Sunlight exposure
- Chemical exposure
All references to rubber insulating gloves can be extended to other rubber electrical insulating PPE including sleeves, blankets, line hose, covers, and matting, although these items are often not applicable to industrial, non-utility, and non-contractor situations.
Step 3: Always Inspect Before Use
All of the ASTM F496 In-Service standards contain provisions for Field Care, Inspection, and Storage, which reads as follows:
(8.1) The field care and inspection of electrical insulating gloves and sleeves, performed by the individual, is an important requirement in providing protection from electric shock. Defective or suspected defective gloves and sleeves shall not be used but returned to an electrical testing facility for inspection and retest. Gloves or sleeves shall not be bundled together with tape.
(8.2) Insulating gloves and sleeves shall be visually inspected by the wearer for defects. Gloves shall be air-tested before use each day and at other times if there is cause to suspect any damage. They shall be inspected over the entire surface and shall be rolled gently between the hands to expose defects and imbedded materials.
(8.3) Insulating gloves shall be given an air test by rolling the cuff tightly toward the palm in such a manner that air is entrapped inside the glove, or by using a mechanical inflator.
Puncture detection may be enhanced by listening for escaping air. While examining the gloves for punctures and other defects, be sure to hold the gloves against the worker’s cheek to feel for escaping air, which would indicate a hole in the glove. Next, reverse the glove to check the inside, and repeat the process.
A portable, mechanical inflator may also be used in the field to enhance the inspection of the glove and identification of any damage. Simply affix the glove to the inflator and pump it up to view any damage to the glove that is not visible when not inflated. The use of two-color rubber insulating gloves can also aid in the identification of problems, since any damage to the outer layer reveals the contrasting color of the inner layer.
Last but not least, there is a rubber insulating glove inflation tool designed to fit inside the glove bag that makes the daily field visual inspection of rubber insulating gloves easier than ever. Just slide the tool over the cuff edge to trap air inside the glove and roll to inflate. Scuffs, scratches, nicks, age, and ozone damage can also be seen using this technique.
And don’t forget to check your leather protectors every day as well, as dirt and grime can hide damage. Be sure to inspect for embedded wires or metal shavings that could puncture or damage your rubber gloves.
Step 4: Use Proper Storage
When not in use, store rubber insulating products in a suitable container, such as a canvas bag designed specifically for that purpose.
It is permissible, according to ASTM F496, to store rubber gloves inside of their leather protectors, but exercise good judgment. If the leather gloves are wet or damp from working in inclement weather, remove them from the rubber gloves to allow them to dry. Also remove the leather protectors so that the rubber gloves and leather protectors can both be inspected before the start of the next work day.
There are several field storage options available for rubber insulating sleeves including sleeve roll-ups, canvas sleeve bags, and combination bags for storing gloves and sleeves together.
Field storage of rubber insulating blankets need to be stored in a bag, box, container, or compartment that is designed for and used exclusively for them.
Line hose and covers must also be stored in suitable compartments, boxes, or bags.
Step 5: Re-Test Periodically
A qualified electrical testing laboratory will help you ensure that rubber insulating products are safe and effective for their intended use.
The National Association of Independent Laboratories for Protective Equipment Testing (NAIL or NAIL4PET) incorporates the only Laboratory Accreditation for electrical equipment test labs program in North America that meets ASTM criteria .
The re-test process involves thoroughly cleaning the products, visually inspecting them for physical damage, performing dielectric testing at the rated test voltage, and marking and packing the accepted products for return shipment.
What Testing Rubber Insulating Products Involves
Upon arrival at the electrical testing facility, the rubber insulating products are carefully washed and dried. Next, a visual inspection is performed to check for physical damage on the exterior and interior of the product.
Rubber insulating sleeves are also inflated with air to check for physical damage that is not visible to the naked eye. Rubber insulating blankets cannot be inflated with air, so they are rolled to stretch the material and expose any physical damage. Line hose are opened up and inspected from the inside out as use and abuse can also cause physical damage.
After cleaning and visual inspection, the rubber insulating products are ready for electrical testing. All products must be electrically tested according to the appropriate ASTM In-Service specification. Rubber insulating gloves are tested by filling them with water and immersing them in water and applying the test voltage. Sleeves are tested by several acceptable means. One of the most efficient techniques is the straight method, which is performed by immersing the bottom cuff opening of the sleeve in a dielectric fluid that is heavier than water while the remainder of the sleeve is filled with water. The sleeve is then submerged in water and the test voltage is applied.
Blankets are electrically tested by placing them between top and bottom electrodes and applying the test voltage.
Line hose pieces are tested with a metal mandrel serving as the inside electrode and a metal form, metal foil, wet fabric, or wet sponge is wrapped around the line hose as the outer electrode. The test voltage is then applied.
Rubber insulating products that have passed the inspection and testing process are marked to identify the test voltage. It is somewhat traditional to also mark the date of test or re-test, but this leaves it up to the individual worker to manage the in-service process. For example, if a company has a policy of re-testing rubber gloves every three months, the line worker must keep track of testing dates and be aware of when those three months have passed. A more effective way to manage the in-service time period is for the electrical testing facility to mark the next test date.
Take special care when returning rubber insulating products to the electrical testing facility, whether it is an independent test lab or the company’s own test lab. The ASTM standard on Field Care, Inspection, and Storage also states “Gloves shall be stored in their natural shape… Gloves and sleeves shall not be stored folded, creased, inside out, compressed, or in any manner that will cause stretching or compression.” After all, these are the products that might save a life – don’t just throw the gloves and sleeves in a box, and do not just strap blankets to a pallet.
There are thousands of people, processes, policies, and procedures all working together to ensure that today’s electrical workers have the safest rubber insulating products and work practices available. It is a continuous process with a single goal: having every worker think safety, work safely, and return home safe and sound at the end of every working day.
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