102 TRESTON - ERGONOMICS | ESD | LEAN Castors play an important role A quality castor is of the appropriate size in relation to the working environment and purpose of the cart. The bigger the castor, the easier it is to move the cart. For example, big castors make it easier to push the cart over thresholds and other similar obstacles. The tread in quality castors withstands wear and tear. The wheel/tread material is not the only factor influencing the usability and easy movability of the cart, as the flooring material also affects how well the castor rolls and moves. Swivel castors are also handy on a cart, making it easy to manoeuver even in small spaces. We recommend using four swivel castors in tight spaces, making it easier to turn and control loads. Strong castor brakes lock the cart in position, making sure that it stays where it is supposed to be. Castors have a big effect in minimizing the start forces needed to get the cart moving as well as in reducing the rolling resistance and therefore play an important role in ensuring proper ergonomics. The amount of force required to move loads with carts depends on a number of factors: • weight and shape of the load • type and condition of floor surface (e.g. smoothness and density) • route taken (e.g. slopes and obstacles) • type of castor, especially the materials used • size of castor • maintenance of castors – cleaning, lubricating and/or replacing castors on a regular basis has a vital effect in maintaining the ride comfort and minimizing the push effort. Carts Task experience is the key to reducing strain Task experience and correct working technique in pushing and pulling play an important role in reducing some measures of biomechanical strain and therefore yield potential for reducing the risk of injury. For example, pulling a lighter weight cart at hip height, with arms outstretched, would result in very high compressive force at the lower back, as opposed to pushing a much heavier cart between shoulder and elbow height, arms closer to body, which results in much less of a compressive force at the lower back. As a reference, see the illustration on the power zones where people have the greatest strength and most comfort. If your goal is to ensure efficient processes and ergonomic working conditions, start by selecting the correct type of cart for the task and then orientating all workers with the physical aspects and best working techniques for the specific task at hand. No matter how fancy the features of your cart, if your workers use bad techniques while performing their tasks with the cart, you are sure to increase the risk of injuries and create inefficiency in processes. If necessary, modify work practices so that workers can perform their tasks and work within their power zone. ! Although there is no exact weight limit that is safe, a weight of 40-50 lbs is heavy to lift for most people and it thus increases the risk of back injury.
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