on 30-Dec-2018 (Sun)

The use of hand tools is ubiquitous and poorly designed hand tools in an industrial plant may affect more than 10% of workers per year.

A review of hand injury statistics in the US showed that hand tools were involved in 9% of all reported disabling injuries. About three- fourths of these injuries are related to manual tool use

In 1994, tool use accounted for 18% of repetitive-motion injuries

Armstrong et al. (1982) observed that the thigh-skinning department of poultry processing plant, the CTD incidence rate was 130 cases per 200,00 hours of work (a value of 10 or above indicates a case that needs attention)

Ideally, a worker should be able to operate a tool with one hand. Therefore the weight of the tool, especially for repetitive use, should not exceed 1 kg (2.2 lb.).

Left-handed people are 5 times more likely to suffer injuries trying to cope with right handed products.

Loads > 10lbs (~5 Kg) should have a handle.

If the tool requires extreme wrist deviation, the usual reaction is to raise the arm to decrease wrist stress. This biomechanical tradeoff increases stresses on the shoulder joint.

Abduction up to 20 reduces excessive load on the shoulder, but as angles increase beyond 20° so the increase in shoulder load leads to an increase in muscle fatigue.

If shoulder abduction exceeds 30° then you get a rapid increase in fatigue.

If shoulder abduction is 30° , then muscles fatigue 3X as fast. If shoulder abduction is 60°, then muscles fatigue 6X as fast.

Tools with "bent" or angled handles or tools with pistol- grips are beneficial where the force is exerted in a straight line in the same direction as the straightened forearm and wrist, especially when the force must be applied horizontally

Tools with straight handles are for tasks where the force is exerted perpendicular to the straightened forearm and wrist, for instance, when the force must be applied vertically.

Shaped tools such as bent-handle tools are effective where most of the tasks are done in the same plane and height as the arm and hand

Handles should be cylindrical or oval in cross section, with a diameter of between 30 mm and 45 mm.

For precision work the recommended diameter for handles is between 5 mm and 12 mm.

For a greater torque large screwdrivers should have a handle diameter up to 50-60 mm.

A handle that is too short can cause unnecessary compression in the middle of the palm. It should extend across the entire breadth of the palm.

Tool handles longer than 100 mm (preferably 115- 120 mm) will reduce the negative effects of any compression exerted.

Crushing, gripping or cutting tools such as pliers or tongs are equipped with two handles. The recommended distance separating handle is between 50 mm and 65 mm. Such a range will fit both male and female users.

Frequent movements of the index finger while operating the trigger of power tools (such as a power drill) poses a considerable risk for both "trigger finger" and "trigger thumb" (tendonitis in the index finger and/or thumb).

A longer trigger which allows the use of two or three fingers to activate them reduces discomfort and minimizes the risk for injury.

The recommended minimum length of the trigger is 50 mm.

to "bend" the tool, not the wrist

use tools with angled or "bent" handles

The condition of tools is an important factor. Blunt or dull tools such as scissors, cutters, saws, screwdriver tips, in fact any tools in a poor state of repair, not only compromise safety but also increase (sometimes by a factor of ten) the effort needed to use them.

Poultry Knife Design (Armstrong, 1982)

Cumulative trauma injury rate more than twice as high among poultry cutters as other workers.

Conventional paint scraper handle design compresses the ulnar artery.

Modified handle rests between thumb and index finger preventing pressure on sensitive regions of the hand (Tichaeur, 1967).

Bent Pliers (Tichauer, 1978)

Biomechanics is concerned with the mechanical elements of living organisms

Occupational Biomechanics deals with the mechanical and motion characteristics of the human body and its elements

Allow us to predict potentially hazardous loading conditions on musculoskeletal components without actual subject risk

F ==> stress ==> injury

The NET tensile force created by ligaments and muscles holding the joint together.

The NET torque created at the elbow joint by muscles.

The 40% additional bending moment created by carrying the load only 6 inches farther from the body

The vertebral column is a vertical series of approximately 33 small bones (known as vertebrae), which are separated by intervertebral discs

It can be separated into five different regions, with each region characterized by a different vertebral structure