The Fatal Four in Construction – Electrocution
Date Posted: 12/12/2023
Statistics show that exposure to electricity is a significant cause of death among construction workers. Among electricians, the most serious concern is working “live” or near live wires instead of de-energizing and using lockout/tagout procedures. Among non-electricians, the significant problems are failure to avoid live overhead power lines and a lack of basic electrical safety knowledge. Electrocutions are the fourth leading cause of death among construction workers in the United States. Electrical workers had the most electrocutions per year, followed by construction laborers, carpenters, supervisors of non-electrical workers, and roofers. In addition to heart attacks and burns, these deaths can occur from falls after contact with electricity. Almost all the construction electrical equipment you work with can cause electrocution (death) if misused.
General Electrical Hazards in Construction
Electricity is the uniform motion of electrons through a conductor (known as electric current). Conductors are materials that allow the movement of electricity through them. Most metals are conductors. The human body is also a conductor.
| Current | Effect |
|---|---|
| 1 mA | Barely perceptible |
| 1-3 mA | Perception threshold (most cases) |
| 3-9 mA | Painful sensation |
| 9-25 mA | Muscular contraction (can’t let go) |
| 26-60 mA | Respiratory paralysis (may be fatal) |
| 60 mA or more | Ventricular fibrillation (probably fatal) |
| 4 A or more | Heart paralysis (probably fatal) |
| 5 A or more | Tissue burning |
Methods to protect yourself and others from the general electrical hazards in construction:
Do not work on energized electrical circuits until all power is shut off (when possible) and placed in an electrically safe condition.
Utilize lock-out/tag-out procedures to prevent the energy from being restarted.
Immediately replace frayed, damaged, or worn electrical cords.
Ensure that all extension (flexible) cords shall have grounding prongs.
Protect extension (flexible) cords from damage, including sharp corners, doorways, and walkways.
Electric tools should be maintained in accordance with the manufacturer and checked regularly for defects and damage. Tools should be removed from service if a fault or damage is discovered.
Ensure that all electric tools are adequately grounded (either three-pronged or double-insulated).
Use Ground Fault Circuit Interrupter (GFCI) protection whenever possible while servicing portable tools and equipment.
Note: Roughly half (49%) of all fatal and nearly a quarter (24%) of nonfatal electrical injuries from 2011 to 2020 occurred in the construction industry. Specialty trade contractors accounted for 71% of fatal electrical injuries and OSHA electrical citations in construction.
Arc Flash/Blast
Arc flash is defined by the National Fire Protection Association (NFPA) as “A source of possible injury or damage to health associated with the release of energy caused by an electrical arc.” Arc flashes occur when energy moves through the air from an exposed live conductor to another conductor or the ground. These events generate extremely high temperatures and pressure waves in addition to the flowing electrical current. Five to ten arc flash incidents occur daily in the United States. Anyone exposed to these events, while unprotected, is at significant risk of severe injury or death. The primary reason why arc flash events and injuries occur is due to working on energized circuits and equipment.
Methods to protect yourself and others from the effects of arc flash include:
Ensure workers are trained and qualified for the task that they will perform.
Read and understand the arc flash warning labels on any circuit or equipment rated at 50 volts or more.
Do not start work without a job safety briefing (safety meeting) to review all potential hazards and applicable safety practices.
Only work on de-energized and locked-out circuits and equipment whenever possible.
Establish safe work practices such as energized electrical work permit process.
Establish boundaries to keep non-essential people clear of the work area.
Ensure that electrical personal protective equipment (PPE) is used. Electrical PPE may include the following:
Leather protective gloves.
Insulated rubber gloves.
Eye and face protection.
Hearing protection.
Non-conductive headgear.
Arc-Flash protective clothing as required by NFPA 70E.
Electrical blankets and barriers.
Hot sticks and similar tools.
Only use insulated and electrically safe tools.
Overhead Powerlines
For non-electrical workers, the leading cause of electrocution was contact with overhead power lines. These deaths resulted from failure to de-energize or protect the power lines and failure to maintain minimum clearance distances from power lines. Electrocutions from metal objects contacting overhead power lines involved 26 electrical workers and 167 other construction workers. The most common examples involved metal ladders, cranes, aerial lifts, trucks, heavy equipment (such as water well drillers, backhoes, concrete pumpers, and dump trucks), wires, metal poles, and metal scaffolds or scaffold parts. Working in cramped areas contributed to 97 electrocutions (6%), about eight deaths yearly. Working in attics or above drop ceilings was a risk for electricians and other construction workers working under houses, in basement crawlspaces, or in attics.
Methods to protect yourself and others from contact with overhead powerlines include:
Contact utility companies in advance to de-energize or insulate overhead powerlines.
Ensure all overhead electrical lines should be located and identified.
Ladders, scaffolds, equipment, and materials should not be placed within 10 feet of overhead powerlines.
Keep metal tools and other conductive objects away from overhead powerlines.
Use a dedicated spotter when a crane travels closer than 20 feet to an overhead powerline.
Minimum Clearance Distances from Overhead Powerlines for Cranes, Rigging, and Personnel Lifting
| Voltage Nominal kV | Minimum Clearance Distance (feet) |
|---|---|
| Up to 50 kV | 10 |
| Over 50 to 200 kV | 15 |
| Over 200 to 345 kV | 20 |
| Over 345 to 500 kV | 25 |
| Over 500 to 750 kV | 35 |
| Over 750 to 1000 kV | 45 |
| Over 1000 kV | Contact a Registered Professional Engineer |
