Pushing, pulling, carrying and mechanical aids

Lifting gets most of the attention, but a great deal of manual handling involves pushing, pulling and carrying. Workers push carts, cages, hospital beds and food trolleys, pull pallet jacks and hose lines, and carry boxes, tools and buckets over long distances. These tasks can strain the back, shoulders and arms, and they add slip, trip and collision hazards. Mechanical aids reduce or remove manual effort, but only if they are well chosen, well maintained and actually used. This lesson explains how to assess and reduce the forces in pushing, pulling and carrying, and how to choose and introduce mechanical aids.

Pushing or pulling?

In most situations, pushing is better than pulling. When pushing, the worker faces the direction of travel and can see where they are going, the body leans into the load using body weight, and both hands are usually in a balanced position. Pulling often means walking backward or twisting to look over a shoulder, with the arms stretched behind and the shoulders and lower back under strain. Pulling may be acceptable for short distances or where pushing is impossible, such as with a manual pallet jack moving forward with the handle in front, which is actually a form of pulling while walking forward. Where possible, design equipment and routes so that loads can be pushed.

Initial and sustained force

Two forces matter when moving a wheeled load. The initial force is the peak force needed to overcome inertia and start the load moving, or to stop it, turn it or move it over an obstacle. The sustained force is the smaller force needed to keep the load moving at a steady speed. Initial forces are typically two to three times sustained forces, and they are most likely to cause sudden strains. Both can be measured with a push-pull force gauge placed between the hands and the handle.

On a level floor, the sustained force needed to roll a load depends on its mass and on the rolling resistance of the wheels and floor:

The coefficient of rolling resistance \( \mu_r \) is small for large, hard wheels on smooth, hard floors, roughly 0.01 to 0.02, and much larger for small or soft wheels, carpet, gravel, worn bearings or wheels clogged with debris, sometimes 0.05 or more. On a slope, the component of the load's weight along the slope adds to the force, often far more than rolling resistance does.

Reducing push and pull forces

Push and pull forces can be reduced at every stage of design and maintenance:

• Reduce the load per trip, or the weight of the cart itself.
• Choose larger-diameter wheels and casters, with tread materials suited to the floor: harder treads such as polyurethane roll more easily on smooth floors, while softer treads absorb shocks on rough floors.
• Choose wheel bearings that roll freely, and maintain them: clean debris, lubricate and replace worn or flat-spotted wheels on a schedule.
• Place swivel casters at the handle end for steering, or use carts with central fixed wheels for straight-line movement.
• Keep floors smooth, level, clean and free of gaps, thresholds and cables; repair potholes and uneven joints. Avoid carpets on routes used by carts.
• Avoid ramps and slopes where possible, and make unavoidable ramps as gentle as practical.
• Provide handles at a height between hip and elbow (roughly 90 to 115 cm, or 35 to 45 in, for most adults), or vertical handles that allow each worker to choose a comfortable height.
• Use powered carts, tugs, powered pallet jacks and motorized beds for heavy loads, long distances, slopes and frequent moves.
• Provide enough space to maneuver, and plan routes to avoid tight turns, doors that must be held open and crowded areas.

For more detailed assessment, measured forces can be compared with the Liberty Mutual tables, which give maximum acceptable initial and sustained forces for given percentages of male and female workers, based on handle height, distance and frequency. ISO 11228-2 offers a similar method.

Carrying

Carrying combines holding a load, which loads the back, shoulders and arms statically, with walking, which adds balance demands and trip hazards. Risk increases with the weight of the load, the distance carried, the frequency, and the posture: loads carried far from the body, on one side, above shoulder height, or blocking the view are particularly hazardous. One-handed carrying, such as carrying a bucket or toolbox, loads the spine asymmetrically and bends the trunk to the side.

• Carry loads close to the body, between knuckle and shoulder height, with the arms close to the trunk.
• Split loads between both hands, such as two half-full buckets instead of one full one, or use a two-handed container.
• Keep carrying distances short; as a guide, consider carts or other aids whenever loads are carried more than about 10 m (33 ft) or carried repeatedly.
• Make sure the carrier can see over or around the load and that the route is clear, well lit and free of stairs where possible.
• Use shoulder straps, carrying frames, panel carriers and harnesses to improve grip and distribute load.

Mechanical aids

Mechanical aids range from simple tools to automated systems. Choosing the right aid starts with understanding the task: what is moved, how often, how far, between which heights, in what space and by whom.

Making mechanical aids work

Many workplaces buy mechanical aids that then sit unused in a corner. Workers do not use aids that are slow, hard to find, awkward to use, poorly maintained or unsuitable for the task, especially under time pressure. To make aids work:

• Involve workers in choosing and trialling equipment before buying it.
• Make sure the aid fits the task, the loads, the space and the pace of work. An aid that doubles the time of each lift will not be used when quotas are tight.
• Keep aids where they are needed, with clear storage and charging locations.
• Train workers and supervisors in using the aid and in recognizing when it should be used.
• Maintain aids on a schedule and make it easy to report and repair faults.
• Adjust production standards and quotas to allow time to use the aid.
• Check that the aid does not introduce new hazards, such as pinch points, collisions with pedestrians, tipping or electrical hazards.

Pushing and pulling special loads

Some loads need special care. Hospital beds, stretchers and loaded wheelchairs combine high mass with the need for careful control; many health care facilities now use powered bed movers. Tall cages and roll containers can tip over if pushed from the bottom, turned too quickly or pushed over thresholds; push them from the side at handle height and keep heavy items low. Manual pallet jacks should be used only for loads and distances within their design, with powered jacks for heavy loads, long distances or slopes. Hose lines, cables and ropes should be pulled with the body facing the direction of travel when possible and with good footing.