1. Chapter 14 Handtools Learning Objective 1
State Human Factors/Ergonomic principles that influence the performance and safety of work systems (workers, equipment, and work processes).
Learning Objective 2
Apply HF/E guidelines and use standard HF/E tools (e.g., RULA, NIOSH Lift Equation) in the design of work systems.

2. Handtools Extend the capability of the hand Selection criteria:
What the tool can do
How the tool is used

3. Guideline 1: Use Special-Purpose Tools
Benefit: Performs well tasks that are repeated many times/week
Costs: Capital, maintenance, utility
Analysis:
Estimate years of use and usage/year
Divide total cost by usage
Compare to savings
Tool Selection
Base on detailed analysis, not just capital cost.
Benefits include savings beyond just labor savings (capability, quality, etc.)

4. Handtool Selection Steps
Do a job analysis.
Identify tool-use issues:
Operating forces
Repetitions per minute or per shift
Postures
Workpace
Select the right tools.

5. Guideline 2: Design Tools to Be Used by Either Hand
The tool should be in the user’s preferred hand.
Strength, dexterity, and performance are greater for the preferred hand.
Benefits:
Includes the 10% of the population that is left-handed.
Allows non-preferred hand to be used when the preferred hand is engaged or resting.

6. Handgrip Strengths

7. Gloves Protect the hand against Decrease force grip. May abrasion
impact
chemicals
heat, cold
cuts, infection
vibration.
Decrease force grip.
May
decrease manual dexterity
increase assembly time.

8. Guideline 3: Power with Motors More Than with Muscles
Mechanical energy is 10 to 1000 times cheaper than human.
Motors extend capability and do not fatigue.
Motors permit a larger percent of workforce to do the job.

9. Reducing Hand–Arm Vibration Syndrome
Use a process with zero or low operator vibration.
Use equipment with low levels of vibration.
Use equipment with vibration-isolated handles.
Avoid resonance.
Furnish vibration-isolated gloves.
Encourage workers to follow VS-reducing practices.

10. Guideline 4: Use the Proper Grip
Power grip
Semipower grip
Precision grips

11. Power grip Tool handle perpendicular to the forearm axis.
Direction of force:
Parallel to forearm
At an angle to forearm
Applied as torque about forearm

12. Power Grip

13. Semipower Grip Fingers act as a group but thumb position changes.
Oblique grip: thumb aligned along tool axis
Hook grip: fingers wrap around tool, thumb is passive
Hook grips are preferable to pinch grips.

14. Precision Grip Has about 20% strength of a power grip.
Internal precision grip (e.g. table knife)
External precision grip (e.g. pencil)
Forearm or tool may be supported.

15. Guideline 5: Make the Grip the Proper Thickness, Shape, and Length
Hand Sizes
Are larger with gloves.
Tend to be larger for men than for women.
Grip Diameter
For power grip, 35 mm to 45 mm is optimal.
For precision grip, use 9.5 mm to 12.7 mm.

16. Grip Shape Section Perpendicular to Grip Axis
Prevent rotation and slippage.
Use thumb conoid (tab) or noncircular cross-section.
Improve coefficient of friction of handle.
Section Along Tool Grip Axis
Keeps tool from moving forward and backward in hand.
Allows force exerted along tool axis to be greater.
Can act as a shield.

17. Grip Shape (cont.) Length
For power grip, all fingers must make contact.
For external precision grip, shaft must be supported.
For internal precision grip, tool must extend past palm but not as far as wrist.

18. Guideline 6: Make the Grip Surface Smooth, Compressible, and Nonconductive
Smoothness reduces pressure points.
Compressibility minimizes pressure on the hand.
Nonconductivity reduces heat and cold problems and risk of electric shock.

19. Guideline 7: Consider the Angles of the Forearm, Grip, and Tool
Keep the wrist in neutral position.
Best angle varies with posture.
Consider changing the job to improve angle.
Consider pistol-grip or bent tools.
Clearance
Increase distance from hot surfaces to reduce burns.
Provide shield from heat.
A narrow neck reduces heat transfer.
Avoid pinching risk with repetitive-use tools.

20. Joint Angles
Source: Canadian Centre for Occupational Safety and Health, OSH Answers: Ergonomics,
last accessed 19 May 04

21. Guideline 8: Use the Appropriate Muscle Group
Muscle Direction
Strengths and ranges of motion differ.
Consider normally-open tools.
Give muscle something to push against.
Muscle Size
Consider moment arm.
Provide power grip.

22. Guideline 8 (cont.): Use the Appropriate Muscle Group
One versus Many
Use fingers in combination.
Pinch types vary greatly in strength..
Consider trigger strips instead of buttons.
Consider alternate types of triggers.
Rotate Inward
Hand and arm can rotate 70º clockwise, 150º counterclockwise.
Muscle Time
Reduce time the muscle is used.
Use clamping tools, locking triggers, discrete controls, straps.
Consider guides or funnels for positioning.

23. Examples

24. Knives
Source: Intercodev, last accessed 19 May 04

25. Knife with upright handle
Source: Intercodev, last accessed 19 May 04

26. Knife with upright handle
Source: Intercodev, last accessed 19 May 04

27. Ergonomic Pliers
Source: Wiha Quality Tools,
last accessed 16 Nov 09

28. Wire Stripping Pliers
Source: MichaelHoligan.com,
last accessed 19 May 04

29. Scissors
Source: Intercodev, last accessed 19 May 04

30. Scissors
Source: Intercodev, last accessed 19 May 04

31. Handles
Source: Intercodev, last accessed 19 May 04

32. Ratchet Screwdriver
Source: Lara Specialty Tools, last accessed 19 May 04

33. Ratchet Screwdriver last accessed 19 May 04
Source: Pro’sKit, New Product Release …,
last accessed 19 May 04

34. Hammers
Source: ContractorsTools.com,
last accessed 19 May 04

35. Coiled-Handle Hammer
Source:NIOSH/Ergonomic Interventions in Ship Building/Coiled Hammer Handle,
last accessed 19 May 04

36. Ergonomic Hand Tools Links
humantech Vendorweb
NIOSH Guide