Solution Summary: Using Insulating Blankets and Sheets
Using insulating blankets and sheets are work practices that can protect workers from electrical hazards. Blankets can be wrapped around the equipment and fastened down to provide a barrier between workers and any source of electrical current. Blankets are also safe alternatives when there are no cover up equipment on live lines or when cover up equipment are not appropriate for irregularly shaped hardware.
Insulating blankets and sheets can provide primary shock protection when workers are working on or near live lines. Insulating blankets must conform to ASTM D1048 specifications and are reusable, but should be periodically inspected and tested. There are different types of blankets used for various applications. While a blanket may be used during a certain job, the level of protection may be inadequate for that job. ASTM class blankets must be appropriate for the work condition. Different types of blankets are classified based on their voltage ratings (Table 1).
Table 1. ASTM Class Voltage Ratings (adapted from Lawrence Berkeley National Laboratory: Electrical Safety Manual)
There are three types of insulating blankets: (1) Roll Type Blankets, (2) Eyelet Type Blankets, and (3) Low Voltage Blankets.
(1) Roll Type Blankets
Roll type blankets are versatile, as they are easy to store, install and remove (Figure 1). In addition, they are flexible, highly tear-resistant, and flame-, oil- and ozone-resistant. The advantage of this type of blanket is the ability to custom cut it on the jobsite to conform to specific requirements. This decreases the number of insulating blankets required at the job. One blanket roll can be turned into two or three separate blankets. The disadvantages to roll type blankets include limitations in voltage ratings and the need for clamp fasteners, which create a slight risk of slipping if not properly secured.
Figure 1. (a) Insulating roll blanket (Source: http://www.mitchellinstrument.com); (b) Roll blanket application (Source: https://www.grainger.com)
(2) Eyelet Type Blankets
Eyelet style blankets are flexible blankets that are secured using pins, snaps or manufacturer-specific straps. Eyelet styles also are available with a zip-on edge attached to a nylon-threaded border for quick and safe installation (Figure 2). The advantage to the eyelet blanket is that there is almost no risk of leaving voids in the workspace, ensuring maximum safety for workers. However, they must be stored in a relaxed position, cannot be folded or rolled in any way, and cannot have anything placed on top of them with the exception of other blankets.
(3) Low Voltage Blankets
Low voltage blankets are an economical solution for covering equipment that presents minimal risk for workers contacting live parts. Insulating blankets are available with or without the hook and pile (zip) or plain style (Figure 3-a).
Figure 2. Different colors of Eyelet Style (Source: http://www.westernsafety.com)
Insulating sheets provide primary shock protection when workers are working adjacent to energized lines (Figure 3). Insulating sheets must conform to ASTM F2320 specifications. The sheets are disposable and can be precut. However, the precut sections must be used within 6 months or else they must be discarded. These sheets are not intended to provide permanent barriers or insulating applications (Figure 3-b). Different types of insulating sheets with various voltage ratings are shown in Table 1.
Note: Polyvinyl chloride insulating sheets can protect workers from shock incidents while working on energized lines. PVC insulating sheets must conform to ASTM D1742 specifications. This is “one use” material. A PVC sheet’s life after cutting is 6 months. Only ASTM classes 0 and 1 are available for PVC insulating sheets. The most important advantage of this kind of sheeting is that it is clear (Figure 3-c).
Figure 3. (a) low voltage blankets (Source: http://www.westernsafety.com); (b) Insulating sheeting (Source: Lawrence Berkeley National Laboratory: Electrical Safety Manual); (c) PVC insulating sheeting (Source: Lawrence Berkeley National Laboratory: Electrical Safety Manual)
Electrical hazards are one of the common hazards in the construction industry hazards that cause serious injuries and death. Contact with electric current is a major cause of injury and death among construction workers (Janicak 2008). In 2012, the Census of Fatal Occupational Injuries (CFOI) data produced by the Bureau of Labor Statistics (BLS) indicated that contact with electric current was the fourth leading cause of work related deaths—after falls, transportation incidents, and contact with objects and equipment (BLS 2012). Electricity can cause electric burns, electrocution, shock, arc flash/blast, fires and explosions. One of the major causes of an electrocution is contact with overhead powerlines and energized sources. Overhead powerlines are particularly hazardous since they carry high-voltage electricity. Although electrocution is considered the main risk, other important hazards of working near or on high-voltage lines include electrical shock, burns, and falls to lower levels. These types of hazards happen when the body becomes part of the electric circuit, whether by direct contact with an energized source or by contact with a conductive material that has become energized. The severity of the electrical hazard depends on several factors, including the length of exposure time, energy deposited into the body, the pathway through the body, wetness or dryness of the surface and the amount of current. The best and preferred method of control is to keep a safe distance from power lines. Table 2 shows the minimum safe distance for various line voltages:
Table2. Minimum powerline clearance distances (Source: 29 CFR 1926.1408(h))
If a qualified worker must be closer than the safe distance to an energized line, the energized electrical conductors must be insulated from the worker and any other conductive objects. In this situation, the combined use of insulating blankets and sheets can prevent injury and death by providing protection from electrical shock. These insulation blankets and sheets can cover exposed live parts that may come in contact with parts of the worker’s body that may not fully protected with appropriate PPE.
How Risks are Reduced:
Basic protection against shock hazards is to use insulations and barriers. Using insulating blankets and sheets prevents unintentional contact with live parts. Consequently, this can decrease the risk of electrical accidents because using insulating blankets and sheets create barriers against the flow of electrical current.
Effects on Productivity:
The risk of unintentional contact with live lines is eliminated when workers (e.g., lineman, electrician, and etc.) cover energized lines or equipment with insulating blankets and sheets. Using insulator equipment can improve productivity, eliminating the need to spend time contacting utility companies to de-energize lines and then follow all grounding processes to ensure de-energizing (it should be noted that de-energizing is the safest route for working around electrical equipment/lines). Generally, when workers feel safe working on live lines, they will be more productive.
Using insulating blankets and sheets are also safe alternatives to using cover up equipment on live lines or when cover up equipment are not appropriate for irregularly shaped hardware. It should be noted that it should not be relied on insulating blankets and sheets as the first line of protection to prevent electrocution, PPE and other solutions must also be used in conjunction with insulating blankets and sheets.
Maintenance and testing:
- Insulating blankets are reusable but they should be periodically inspected and tested. Inspection should conform to ASTM F1236, and damaged or defective blankets must be removed from service. The test date must be stamped on the blankets.
- Insulating blankets and sheeting must be stored in a dark, cool and dry location away from chemical materials and vapors and electrical discharges. Blankets must be cleaned with lukewarm water and mild soap detergent and rinsed thoroughly.
- The shelf life of the blankets is 12 months, and blankets may be issued any time during this shelf life.
- No markings except for a testing stamp may be applied to the blankets and sheets.
IMPORTANT: Insulating equipment with any of the following defects may not be used [1910.137(c)(2)(iii)]:
- A hole, tear, puncture or cut [1910.137(c)(2)(iii)(A)]
- Ozone cutting or ozone checking (that is, a series of interlacing cracks produced by ozone on rubber under mechanical stress) [1910.137(c)(2)(iii)(B)]
- An embedded foreign object [1910.137(c)(2)(iii)(C)]
- Any of the following texture changes: swelling, softening, hardening or becoming sticky or inelastic [1910.137(c)(2)(iii)(D)]
- Any other defect that damages the insulating properties [1910.137(c)(2)(iii)(E)]
- Insulating equipment found to have other defects that might affect its insulating properties shall be removed from service and returned for testing under paragraphs (c)(2)(viii) and (c)(2)(ix) of this section [1910.137(c)(2)(iv)].
- Insulating equipment shall be cleaned as needed to remove foreign substances [1910.137(c)(2)(v)].
- Insulating equipment shall be stored in such a location and in such a manner as to protect it from light, temperature extremes, excessive humidity, ozone, and other damaging substances and conditions [1910.137(c)(2)(vi)].
Behzad Esmaeili, Ph.D. - University of Nebraska- Lincoln
Sogand Hasanzadeh - University of Nebraska- Lincoln
Pouya Gholizadeh - University of Nebraska- Lincoln
Brett Farquhar - University of Nebraska- Lincoln
Erik Bruening - University of Nebraska- Lincoln
- Install and maintain electrical control systems
- Install and maintain temporary wiring systems on construction sites
- Install and repair high voltage lines, transformers and switches
- Work with or remove old wiring
Hubbell Power Systems
To obtain information, visit http://www.hubbellpowersystems.com/ or contact 1-573-682-5521
Salisbury by Honeywell
To obtain information, visit https://www.salisburybyhoneywell.com or contact 1-877-406-4501
Estex Manufacturing Company
To obtain information, visit http://www.estexmfg.com or contact 1-800-749-1224