EHS 218 Occupational Ergonomics Hand Tools

Types of Grip  Power –Hands wrap around the handle –Capable of generating more force than others with less exertion  Precision –Internal and external –Avoid when possible, especially for long duration tasks –Muscles usually not at mechanical advantage –Inefficient generation of power

Factors of Concern in Hand Tools Static muscle loading Awkward hand positions Pressure on tissues or joints Vibration and noise Pinch points

Factors of Concern in Hand Tools Static Muscle Loading Shoulder –Abduction if forces are applied with a straight tool on a horizontal workplace Forearm –Stress in forearm when repetitive work is done with elbow extended –Heavy gripping to keep hand from slipping off tool Fingers and hand –Continuous holding or application of force results in fatigue or loss of finger flexibility

Factors of Concern in Hand Tools Awkward Hand Positions Grip strength is greatest when wrist is straight Strength is lost as the wrist moves from neutral The more bent the wrist, the more stress on the tendons and nerves

Grip Strength

Grip Strength and Gender

Factors of Concern in Hand Tools Pressure on Tissues or Joints Palm –The tool can press into the palm at the base of the thumb where blood vessels and nerves pass through the hand Finger –Force exerted by fingers can put high pressure on skin or joint

Factors of Concern in Hand Tools Vibration and Noise Power tools are noisy (>75dB) and vibrate at Hz At these frequencies the vibratory energy can cause circulatory dysfunction in the hands The weight of the tool may require a tight grip, contributing to the effect of vibration The effects are exacerbated in cold weather

Factors of Concern in Hand Tools Pinch Points Fingers can be caught between the parts of a double-handled tool Problematic especially when large forces are exerted

Basic Principles of Tool Design Fundamentals Avoid high contact forces and static loading Avoid awkward positions Avoid repetitive finger action Avoid tool vibration

Design and Selection of Tools Handle length Handle diameter Handle span Switches and stops Tool weight and suspension Torque Pressure points Vibration Handle slipperiness Shape Temperature Handedness Gender

Design and Selection of Tools Handle Length Minimum = 4 inches; Maximum = 5 inches Add 1/2 inch when gloves are used Handles that are too short don’t allow all of the fingers to grip

Design and Selection of Tools Handle Diameter Grip strength diminishes as the fingers are spread apart Power grips: inches (1.5 inches ideal) Precision operation: inches (0.45 inches ideal) For cutout handle, L = 5 inches, W = 2.5 inches

Design and Selection of Tools Handle Span For tools with two handles, the distance between handles should be inches at location of greatest force

Design and Selection of Tools Switches and Stops Holding in the “on” position causes unnecessary static posture Pay attention to center of gravity Location of switches should take into consideration stabilization of tool Allow for stabilization with other hand Or use stops or guards to assist in stabilization

Design and Selection of Tools Tool Weight and Suspension Weight of tool will determine how long it will be held Tools weighing > 5 lb. and must be supported by arms held away from body will likely cause fatigue Counterbalance tools when possible

Design and Selection of Tools Torque Reduce torque requirements Allow for assistance with both hands Increase diameter of tool if necessary

Design and Selection of Tools Pressure Points Avoid hard or sharp edges that may dig into tissue

Design and Selection of Tools Vibration Dampen vibration when possible Use alternate tool if available Use minimal force necessary Take frequent rest breaks Avoid working in cold environment with vibrating hand tool

Design and Selection of Tools Handle Slipperiness Handles should be non-porous, non-slip, and non- conductive Avoid glossy paint or highly polished surface Use rubbers or plastics Grasping surfaces should be slip resistant Use porous safety-tape instead of gloves Use special absorbent sleeves over handles

Design and Selection of Tools Tool Shape Avoid form fitting handles When fingers are stretched apart to fit form fitting handles, power is lost and operation is difficult

Design and Selection of Tools Temperature Hazards when working in cold temperature due to vasoconstriction Provide proper gloves Minimize vibration Minimize force requirements Allow for frequent rest breaks

Design and Selection of Tools Handedness Reduce the handedness of tools when possible How is the force applied and used? Can either hand hold/operate the tool? Can the tool be moved in the direction of force equally well by either hand? Is the workpiece equally visible when operating with both hands? How is the force controlled? Can both hands exert the controlling force with equal ease?

Design and Selection of Tools Gender and Age Remember females and different strength requirements Remember older workers and decreased strength capabilities

Design Guidelines for Hand Tools General Guidelines Grip surface smooth, slightly compressible and non-conductive Bend the tool, not the wrist Avoid vibration, particularly Hz Design handles for use by either hand Keep the wrist straight Tool weight balanced about grip axis Eliminate pinching hazards Use special purpose or modified tools!

Keep the Wrists Straight

Bend the Tool, Not the Wrist

Examples of Household Products

Guidelines for Repetitive Work with Hand Tools Use jigs and fixtures when possible Work at proper heights and orientation Re-sequence jobs to reduce repetition Automate highly repetitive operations Allow self-pacing of work when possible New workers should start at slower rate Allow frequent rest pauses