Canadian Rental Service

Safety First and Last: Safe MEWP operation is a matter of attention

By Jeff Thorne   

Features Business Intelligence education

Mobile elevated work platforms are common in many environments as a temporary means of working at height safely. As their popularity has grown there has been an increased concern regarding crushing incidents, specifically where the operator or another occupant has become trapped between the guardrail or the controls of the platform and another object or overhead obstruction.

Let’s look at how these crushing incidents happen. Based on recent studies from the U.K., many of these incidents were a result of human error. There are a few main factors attributed to operator error: slips, lapses in judgment and mistakes.

Slips are associated with familiar routine tasks that are typically skills-based. Slips are the operator’s failure to carry out tasks as they intended. An example may be selecting the wrong control or moving the control in the wrong direction. We all “slip-up” sometimes, right?

Lapses can be judgement-based or where we forget to carry out a specific action or lose our spot in a sequence of actions. An example of this could be moving the boom in an incorrect sequence or failing to consider the rotation of the boom when operating drive controls.

With respect to operating a MEWP, mistakes can be defined as an error in planning, where people do the wrong thing believing it was correct. Mistakes can be rule-based or knowledge-based. A rule-based mistake occurs in many cases out of familiarity with that rule or procedure. For example, an operator may be familiar with how to operate a specific device and have become familiar with the operating control configuration. They may then fail to check the control configuration on a new device prior to use.


A knowledge-based mistake typically occurs when we problem solve or fail to form a plan to achieve a goal. This may be a result of a lack of knowledge or poor reasoning. An example of a knowledge-based mistake could be a lack of awareness of the hazards where an untrained operator takes on a task they shouldn’t due to slopes, grades, wind, load or proximity to electrical hazards.

An international study identified that operators choosing the incorrect control for the movement they wish to make accounted for 21 per cent of incidents. Approximately 60 per cent of incidents had incorrect operation of controls as a possible causal factor. This isn’t hard to do. For example, the joystick of one manufacturer’s scissor lift is jointly used for the lift and drive functions. The operator must change the button below to either the lift or drive function prior to performing the movement. It isn’t hard to imagine someone forgetting to hit the button and inadvertently driving when they mean to lift, or vice versa.

With experienced operators, slips and lapses are typically a result of familiarization and complacency with the equipment and the environment. Rule- and knowledge-based mistakes occur most often with untrained individuals.

If slips and lapses are commonly occurring because of the operator selecting the wrong control, we should give feedback to the manufacturer to make sure displays and controls are clear. Operators must focus and pay attention to the action or movement they are anticipating making. We all get distracted, so the operator needs to be constantly checking for hazards that are present in the environment, around the platform and avoid contact with adjacent objects. Changes to the most recent CSA standards for MEWPs call for an assessment and evaluation of the risks related to the task to be performed and the worksite prior to the work commencing. It sets an expectation for the risk assessment to be understood by the user, and the control functions communicated to the worker.

Decisions on the use and operation of the MEWP should always be made with due consideration for the fact that the machine will be carrying persons whose safety is dependent on those decisions as well as others operating in the vicinity. Stay safe everyone!  

Jeff Thorne is manager of training at Occupational Safety Group

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