Define the concept of 'contact stress' and provide three workplace examples where this ergonomic risk factor is prevalent, and discuss measures to mitigate it.
Contact stress, in the context of ergonomics, refers to the localized pressure exerted on the body by hard or sharp edges, surfaces, or tools. This pressure can compress soft tissues such as skin, muscles, tendons, and nerves, which can lead to discomfort, pain, and ultimately musculoskeletal disorders (MSDs). Unlike general pressure exerted over a wide area, contact stress is concentrated in a small area, creating a higher force per unit area. This concentrated pressure can restrict blood flow, cause nerve compression, and contribute to inflammation and tissue damage. Contact stress is often overlooked because it may not seem as immediately hazardous as forceful exertions or awkward postures, but sustained contact stress can lead to chronic and debilitating MSDs over time. This is why awareness and prevention are crucial in ergonomic design.
The severity of contact stress depends on various factors, including the shape and hardness of the contact point, the force applied, the duration of contact, and the individual susceptibility of the person. For instance, prolonged contact with a sharp edge will have a greater effect than contact with a rounded edge. The human body is not designed to withstand repeated or prolonged exposure to concentrated forces, which is why preventing contact stress is an essential component of workplace ergonomics.
Here are three workplace examples where contact stress is prevalent:
1. Assembly Line Work: Many assembly line jobs involve workers leaning against a hard workstation edge while performing their tasks. The edge of the assembly bench or table can cause concentrated pressure on the forearms, wrists, and abdomen as the workers reach and manipulate parts. For example, workers assembling electronic components might lean against a hard table edge for prolonged periods. The repeated contact with the edge compresses nerves and soft tissues in the forearms and wrists which could lead to nerve compression disorders such as carpal tunnel syndrome or cubital tunnel syndrome. They might also use hand tools repeatedly, which, if improperly designed, can apply contact stress on the fingers and palm resulting in conditions such as hand-arm vibration syndrome, or trigger finger.
Mitigation Measures: To mitigate contact stress in this scenario, workstations should be redesigned with rounded edges or padded armrests. Workers can use gel pads or similar cushioning where they are in contact with the workstation. Anti-vibration gloves should be provided for employees working with vibrating tools, and workers should receive training on using tools correctly to minimize contact stress and reduce force exerted during use. Using jigs or fixtures can reduce or eliminate the need for workers to hold components in their hands for prolonged periods of time.
2. Data Entry and Computer Work: Prolonged use of computer keyboards and mice can also lead to contact stress. For example, resting the wrist on a sharp edge of a desk, or using a mouse with a hard casing repeatedly, can put pressure on the carpal tunnel, causing carpal tunnel syndrome. Similarly, using a hard keyboard without a wrist rest can compress the nerves in the wrists. The constant contact between the forearms and the hard edge of the desk can contribute to elbow pain or ulnar nerve entrapment, and using arm rests with sharp edges can also cause pain. The edge of a desk against the legs or thighs while sitting for prolonged periods can affect circulation and cause numbness or tingling.
Mitigation Measures: Using ergonomic keyboards with a built-in wrist rest can help reduce pressure on the carpal tunnel. Padded mouse pads that support the wrist and reduce pressure are also effective, as well as a split keyboard that supports neutral wrist positions. Ergonomic desk chairs with armrests that can be adjusted to support the forearms without hard contact are important. Soft, rounded edges on desks can also help to reduce pressure on the arms and thighs. Regular breaks to allow workers to reposition and rest from prolonged desk work are also essential.
3. Material Handling: Workers involved in manual material handling are at high risk of experiencing contact stress. When lifting and carrying loads with sharp edges or awkward shapes, the edge of the load can press into the hands, fingers, forearms, and shoulders. For example, workers carrying boxes with sharp edges might experience concentrated pressure that can cause discomfort or pain and can ultimately lead to tissue damage. Similarly, workers pushing wheeled equipment, such as a cart, might experience contact stress on the hands from gripping hard or poorly designed handles for extended periods. Improper tool design, such as small handles on tools that require high force exertion, also causes stress points on the hand.
Mitigation Measures: Using appropriate handles or gloves that provide cushioning can reduce pressure on the hands, and protective guards can help prevent contact with sharp edges. Redesigning the shape of the load with rounded edges and using straps or other devices to secure the load, can help reduce pressure and improve the grip when handling. Using material handling equipment like carts and dollies can minimize the need to carry heavy objects manually, thus eliminating the pressure points on the body. Gloves with padded palms can help absorb pressure and reduce the risk of developing contact stress injuries. Regular rotations of work tasks can help minimize the exposure to these specific stress points, as well as scheduled breaks so workers can get rest periods and allow their bodies to recover.
In each of these examples, mitigating contact stress involves a combination of ergonomic design, the use of appropriate equipment, and workplace modifications, along with worker education and training on recognizing these specific types of hazards. By identifying and addressing these risk factors, workplaces can create safer environments that minimize the risk of MSDs and improve employee well-being and productivity.