Power Tool Safety



Because power tools are so common in construction, workers are constantly exposed to a variety of hazards. The very tool that makes their job easy and efficient may one day be the cause of a tragic accident. It is good to be reminded of good-sense safety practices.

Which Power Tools Cause the Most Hand Injuries?

Considering how often they are used at construction sites, powered hand tools cause relatively few hand injuries in the industry. In 2012, hand injury claims amounted to only about 4.5 percent of all injury claims accepted for the industry as a whole.

It should not come as too much of a surprise that saws, drills, and nail guns account for most of the injuries (67 percent). However, let’s take a look at the top 10 most dangerous portable power tools:

  1. saws (except chainsaws)
  2. drills
  3. nail guns
  4. jackhammers
  5. hand grinders
  6. chainsaws
  7. hand tools not otherwise classified
  8. sprayers-paint
  9. hammers
  10. impact wrenches

(Source: OR-OSHA)

1. Which of the following tool categories accounts for most hand injuries?

a. saws, drills, and nail guns
b. hammers, hand grinders, and drills
c. chainsaws, impact wrenches, and nail guns
d. hand grinders, chainsaws, and hammers


SawStop is a high-quality machine with engineering controls to help prevent table saw accidents.

The exposed moving parts of power tools need to be safe-guarded. Belts, gears, shafts, pulleys, sprockets, spindles, drums, flywheels, chains, or other reciprocating, rotating, or moving parts of equipment must be guarded.

Machine guards, as appropriate, must be provided to protect the operator and others from the following:

  • point of operation (cutting, shearing, punching, etc.)
  • in-running nip points
  • rotating parts
  • flying chips and sparks

Safety guards must never be removed or modified when a tool is being used.

Follow these rules when using circular saws:

  • Portable circular saws with a blade greater than 2 inches (5.08 centimeters) in diameter must be equipped at all times with guards.
  • An upper guard must cover the entire blade of the saw.
  • A retractable lower guard must cover the teeth of the saw, except where it makes contact with the work material.
  • The lower guard must automatically return to the covering position when the tool is withdrawn from the work material.


Protect your hair, scalp, and head. Pull back long hair in a band or a cap to keep it from getting caught in tools or moving parts. Be extremely careful with long hair when using a drill or drill press.

2. Portable circular saws must be equipped at all times with guards if their blades are greater than _____ in diameter.

a. 2 inches (5.08 centimeters)
b. 3 inches (7.62 centimeters)
c. 3 inches (10.16 centimeters)
d. 5 inches (12.70 centimeters)

Operating Controls and Switches

drill press

Power tools must be fitted with safety switches; they are extremely hazardous when used improperly. The types of power tools are determined by their power source: electric, pneumatic, liquid fuel, hydraulic, and powder-actuated.

Constant-Pressure Switches and Controls

The following hand-held power tools must be equipped with a constant-pressure switch or control that shuts off the power when pressure is released:

  • drills
  • tappers
  • fastener drivers
  • horizontal, vertical, and angle grinders with wheels more than 2 inches (5.08 centimeters) in diameter
  • disc sanders with discs greater than 2 inches (5.08 centimeters)
  • belt sanders
  • sander
  • reciprocating saws
  • saber saws
  • scroll saws, and jigsaws with blade shanks greater than 1/4-inch (0.63 centimeters) wide
  • circular saws having a blade diameter greater than 2 inches (5.08 centimeters)
  • chain saws
  • percussion tools with no means of holding accessories securely
  • other similar tools

These tools also may be equipped with a “lock-on” control, if it allows the worker to also shut off the control in a single motion using the same finger or fingers.

3. Drills, belt sanders, and chain saws all have this safety feature in common.

a. They are all used for the same purpose
b. They are all percussion type tools
c. They all use lock-on type switches
d. They require constant-pressure switches and controls
123 rf photo

Positive "On-Off", Constant Pressure, and "Lock-On" Controls

The following hand-held power tools must be equipped with either a positive "on-off" control switch, a constant pressure switch or a "lock-on" control:

  • disc sanders with discs 2 inches (5.08 centimeters) or less in diameter
  • grinders with wheels 2 inches (5.08 centimeters) or less in diameter
  • platen sanders, routers, planers, laminate trimmers, nibblers, shears, and scroll saws
  • jigsaws, saber and scroll saws with blade shanks a nominal 1/4-inch (6.35 millimeters) or less in diameter

It is recommended the constant-pressure control switch be regarded as the preferred device.

4. Which of the following is the preferred power tool control device?

a. The intermittent trigger control switch
b. The positive on-off control switch
c. The constant-pressure control switch
d. The lock-on control switch

Next Section

Portable Tool Use with Extension Cords

extension cord

In construction, extension cords suffer a lot of wear and tear. Most often, the damage is only to the insulation, exposing energized conductors. When a person handling the damaged cord contacts the exposed wires while holding a metal tool case or contacting a conductive surface, serious electrical shock can result, causing a fall, physical injury, or death.

Repairing Extension Cords

When a worker at a construction site inspects an extension cord and determines that it needs to be repaired, who can repair it?

Anyone who is qualified can repair damaged electrical cords, but in most cases the best practice is to discard the cord. The worker does not have to be a licensed electrician to repair a typical extension cord. However, he or she must have the knowledge and skills to repair the cord correctly, understand the hazards involved in making the repair, and be able to describe what could happen if the repair is done wrong. The employer is responsible for determining if the person is qualified. The basis for the determination is normally from the electrical industry perspective. (Source: OR-OSHA)

5. Most often, the damage to power extension cords is only to the _____.

a. insulation
b. ground wires
c. hot side of the circuit
d. plugs



The term "ground" refers to a conductive body, usually the earth. "Grounding" a tool or electrical system means intentionally creating a low-resistance path to the earth. When properly done, current from a short or from lightning follows this path, thus preventing the buildup of voltages that would otherwise result in electrical shock, injury and even death. View this animation to see what happens when grounding is improper.

Under certain conditions, even a small amount of electric current can result in fibrillation of the heart and death. An electric shock also can cause the user to fall off a ladder or other elevated work surface and be injured due to the fall.

To protect the worker from shock and burns at work, make sure electrical powered tools have a three-wire cord with a ground. They must also be:

  • plugged into a grounded receptacle
  • double insulated
  • powered by a low-voltage isolation transformer

Three-wire cords contain two current-carrying conductors and a grounding conductor. Any time an adapter is used to accommodate a two-hole receptacle, the adapter wire must be attached to a known ground. The third prong must never be removed from the plug. OSHA cites this violation often because they see it often.

6. A common violation OSHA compliance officers cite on construction worksites is _____.

a. extension cords are not of the correct color
b. more than two extension cords are connected in series
c. extension cords are insufficient in length
d. missing ground prongs from plugs

Ground-Fault Circuit Interrupters (GFCI)

Since neither insulation nor grounding protects you from the conditions discussed in the previous section, we must use other protective measures. One commonly required acceptable protective method is a ground-fault circuit interrupter (GFCI).


A ground-fault circuit interrupter (GFCI), is a fast-acting circuit breaker designed to shut off electric power in the event of a ground-fault within as little as 1/40 of a second.

It works by comparing the amount of current going to and returning from the equipment along the circuit conductors. When the amount going differs from the amount returning by approximately 5 milliamperes, the GFCI interrupts the current.

Receptacle Type

The Receptacle Type incorporates a GFCI device within one or more receptacle outlets. Such devices are becoming popular because of their low cost.

Portable Type

Portable Type GFCIs come in several styles, all designed for easy transport. Some are designed to plug into existing non-GFCI outlets, or connect with a cord and plug arrangement. The portable type also incorporates a no-voltage release device that will disconnect power to the outlets if any supply conductor is open. Units approved for outdoor use will be in enclosures suitable for the environment. If exposed to rain, they must be listed as waterproof.


Cord-Connected Type

The Cord-Connected Type of GFCI is an attachment plug incorporating the GFCI module. It protects the cord and any equipment attached to the cord. The attachment plug has a non-standard appearance with test and reset buttons. Like the portable type, it incorporates a no-voltage release device that will disconnect power to the load if any supply conductor is open. Because GFCIs are so complex, they require testing on a regular basis. Test permanently wired devices monthly, and portable-type GFCIs before each use. All GFCIs have a built-in test circuit, with test and reset buttons, which triggers an artificial ground-fault to verify protection. Ground-fault protection, such as GFCIs provide, is required by OSHA in addition to (not as a substitute for) general grounding requirements.

For more information on power tool operation see the Professional Power Tool Guide website.

7. Permanent Ground Fault Circuit Interrupters (GFCIs) should be tested ____ and portable GFCIs tested _____.

a. monthly, daily
b. quarterly, after each use
c. monthly, before each use
d. quarterly, before each workshift

Double-Insulated Tools

double insulated

Hand-held tools manufactured with non-metallic cases are called double-insulated. If approved, they do not require grounding under the National Electrical Code. Although this design method reduces the risk of grounding deficiencies, a shock hazard can still exist.

Double-insulated tools are often used in areas where there is considerable moisture or wetness. Although the user is insulated from the electrical wiring components, water can still enter the tool's housing. Ordinary water is a conductor of electricity. If water contacts the energized parts inside the housing, it provides a path to the outside, bypassing the double insulation. When a person holding a hand tool under these conditions contacts another conductive surface, an electric shock occurs.

If a power tool, even when double-insulated, is dropped into water, the employee should resist the initial human response to grab for the equipment without first disconnecting the power source.

8. Which of the following statements is TRUE regarding double-insulated tools?

a. Double-insulated tools reduce the chance of getting shocked by 100%
b. All double-insulated tools will prevent shock even if submerged
c. You can still get shocked from a double-insulated tool
d. Removing the third ground prong makes a tool double-insulated

Next Section

Personal Protective Equipment (PPE) and Clothing

  • Wear PPE that is proper for the type of work being done.
  • Do not wear gloves when operating a grinder.
  • Do not wear loose-fitting clothes or jewelry that can get caught in moving parts.
  • Do not roll up long sleeves. If you wear long sleeves, be sure they are properly buttoned.
  • Do not wear flammable clothes.
  • Wear safety-toed shoes to protect your feet and toes.
  • Protect your eyes, face, head, and scalp. Only wear ANSI-approved industrial-quality safety glasses or safety shields.
  • Pull back long hair in a band or a cap to keep it from getting caught in moving parts.
  • If necessary, use a proper dust, half-face or full-face respirator.

9. Which of the following is an unsafe practice when working with power tools?

a. Pulling back long hair when working around moving parts
b. Wearing gloves while operating a grinder
c. Making sure long-sleeved shirts are always buttoned
d. Use only ANSI-approved safety glasses and shields


using tool
  • Avoid distractions. Keep your mind on your work. Talking, running, pushing, and scuffling can lead to accidents.
  • Work only at operating speed. Do not use a power tool before it has reached operating speed or while it is coming to a stop.
  • Do not force a tool by applying too much pressure.
  • Use both hands. Use both hands to hold and guide material being sawed.
  • Stand in a safe location. Position yourself to avoid being hit if the tool kicks back.
  • Do not allow wires, cords, or other objects that could get caught in equipment.
  • Do not stand directly behind the equipment.
  • Keep safety guards in place and proper working order.
  • Do not use blades that are cracked or kinked.
  • Keep saw blades sharp and set properly.
  • Know the switch location so you can turn off the tool quickly.

10. Which of the following is a safe practice when operating power tools?

a. Stand directly behind the equipment
b. If cutting is difficult, use more force
c. Work only at the operating speed
d. Hold the material being sawed with one hand

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