The typical aircrete job site has various risk factors for electrocution that should be considered.
High-amp hand-held power tools (such as a drill or paddle mixer)
Extension cords
Water
These three factors are present on nearly every aircrete job site. Combined, they present a well documented serious risk for fatal electrocution. These risk factors can be moderated by using tested ground fault circuit interruptors (GFCI) and with proper use of well maintained cords of appropriate gauge and materials.
This webpage is very appropriate reading for anyone making aircrete: https://www.osha.gov/etools/construction/electrical-incidents
If a human body becomes part of a ground fault while operating a drill or paddle mixer, a circuit breaker won't help.
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The following is taken from National Institute for Occupational Safety and Health
(NIOSH) PUBLICATION No. 98-131 WORKER DEATHS BY ELECTROCUTION
Estimated Effects of 60 Hz AC Currents
1 mA Barely perceptible
16 mA Maximum current an average man can grasp and “let go”
20 mA Paralysis of respiratory muscles
100 mA Ventricular fibrillation threshold
2 Amps Cardiac standstill and internal organ damage
15/20 Amps Common fuse or breaker opens circuit*
* Contact with 20 milliamps of current can be fatal. As a frame of reference, a common household circuit breaker may be rated at 15, 20, or 30 amps.
The presence of moisture from environmental conditions such as standing water, wet clothing, high humidity, or perspiration increases the possibility of a low-voltage electrocution. The level of current passing through the human body is directly related to the resistance of its path through the body. Under dry conditions, the resistance offered by the human body may be as high as 100,000 Ohms. Wet or broken skin may drop the body’s resistance to 1,000 Ohms. The following illustrations of Ohm’s law demonstrates how moisture affects low-voltage electrocutions. Under dry conditions, Current=Volts/Ohms = 120/100,000 = 1 mA, a barely perceptible level of current. Under wet conditions, Current=Volts/Ohms = 120/1,000 = 120 mA, sufficient current to cause ventricular fibrillation. Wet conditions are common during low-voltage electrocutions.
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The following extracts are taken from https://www.osha.gov/etools/construction/electrical-incidents
Due to the dynamic, rugged nature of construction work, normal use of electrical equipment at your site causes wear and tear that results in insulation breaks, short-circuits, and exposed wires. [Flexible Cords and Power Tools] If there is no ground-fault protection, these can cause a ground-fault that sends current through the worker's body, resulting in electrical burns, explosions, fire, or death.
How Do I Avoid Hazards?
• Use ground-fault circuit interrupters (GFCI)s on all 120-volt, single-phase, 15- and 20-ampere receptacles, or have an assured equipment grounding conductor program (AEGCP).
• Follow manufacturers' recommended testing procedure to insure GFCI is working correctly.
• Use double-insulated tools and equipment, distinctively marked.
• Use tools and equipment according to the instructions included in their listing, labeling or certification.
• Visually inspect all electrical equipment before use. Remove from service any equipment with frayed cords, missing ground prongs, cracked tool casings, etc. Apply a warning tag to any defective tool and do not use it until the problem has been corrected.
The normal wear and tear on extension and flexible cords at your site can loosen or expose wires, creating hazardous conditions. [Flexible Cords] Cords that are not 3-wire type, not designed for hard-usage, or that have been modified, increase your risk of contacting electrical current.
How Do I Avoid Hazards?
• Use factory-assembled cord sets.
• Use only extension cords that are 3-wire type.
• Use only extension cords that are marked with a designation code for hard or extra-hard usage.
• Use only cords, connection devices, and fittings that are equipped with strain relief.
• Remove cords from receptacles by pulling on the plugs, not the cords.
• Continually audit cords on-site. Any cords found not to be marked for hard or extra-hard use, or which have been modified, must be taken out of service immediately.
If electrical equipment is used in ways for which it is not designed, you can no longer depend on safety features built in by the manufacturer. This may damage your equipment and cause employee injuries. [Power Tools]
Common Examples of Misused Equipment
• Using multi-receptacle boxes designed to be mounted by fitting them with a power cord and placing them on the floor.
• Fabricating extension cords with ROMEX® wire.
• Using equipment outdoors that is labeled for use only in dry, indoor locations.
• Attaching ungrounded, two-prong adapter plugs to three-prong cords and tools.
• Using circuit breakers or fuses with the wrong rating for over-current protection, e.g. using a 30-amp breaker in a system with 15- or 20-amp receptacles. Protection is lost because it will not trip when the system's load has been exceeded.
• Using modified cords or tools, e.g., removing ground prongs, face plates, insulation, etc.
• Using cords or tools with worn insulation or exposed wires.
If the power supply to the electrical equipment at your site is not grounded or the path has been broken, fault current may travel through a worker's body, causing electrical burns or death. [Flexible Cords and Power Tools]. Even when the power system is properly grounded, electrical equipment can instantly change from safe to hazardous because of extreme conditions and rough treatment.
How Do I Avoid Hazards?
• Ground all power supply systems, electrical circuits, and electrical equipment.
• Frequently inspect electrical systems to insure that the path to ground is continuous.
• Visually inspect all electrical equipment before use. Take any defective equipment out of service.
• Do not remove ground prongs from cord- and plug-connected equipment or extension cords.
• Use double-insulated tools and equipment, distinctively marked.
