Machine & Operator Safety
Risk Assessment 101: How to evaluate and improve your safeguards
October 16, 2007 by Michael Wilson
When it comes to evaluating machine safeguards, people are usually asked: “Are there hazards? Yes/No” and “Is it safe? Yes/No.” These are complex questions that should not be resolved with a simple yes/no answer. Instead, firms should conduct risk assessments to determine how effective their current safeguarding system is and how it can be improved.
First, assemble a team to conduct the assessment, not only to reduce the effects of personal biases but also to ensure that the assessment is comprehensive. Ideally, team members will have experience with the equipment from different perspectives (i.e. machine operator, maintenance worker, etc.).
Before starting the assessment, make sure the team knows that it is to consider what the worst-case scenario would be if there were no safeguards in place.
This “no safeguards in place” approach allows the firm to gain a true understanding of the potential risks associated with the equipment, which in turn enables the company to develop better safeguards.
In Canada, there are three main standards that address machine safety: Canadian Standards Association (CSA) Z432-04 (general safeguarding of machinery), Z142-02 (power presses) and Z434-03 (robots). Both Z432 and Z434 provide general guidelines on how to conduct a risk assessment.
Other resources, such as the ISO 14121-2007 and ANSI B11.TR3-2000, also provide guidance. CSA recognizes this and states that methods similar to the ones laid out in its own standards, or more stringent ones, can be applied to machine safety. Incidentally, Z142 does not contain a clause on risk assessment because it is assumed there is a high level of risk when working with presses.
The actual risk assessment process involves reviewing the operation of the equipment, identifying associated tasks and potential hazards, and using these inputs to complete a risk estimation.
• Review the operation of the equipment. Questions that need to be addressed include: How do operators interact with the machine? How often is maintenance required? How are malfunctions handled? All foreseeable uses and reasonable misuses should be considered.
• Identify specific tasks that can affect workers who come into contact with the equipment. Consider how operators load or remove parts or troubleshoot the equipment. Examine the same activities for maintenance or setup personnel. The activity that brings a worker into contact with the equipment should be taken into account. In some cases, outside contractors may be involved, and these workers also require consideration when assessing risk.
• Identify the hazards. Each task can expose the worker to some kind of hazard. These hazards should not only be identified, but also compiled and reviewed for reference. Hazards can be mechanical: entanglements created by rotating parts, friction and abrasion, and impact or crushing. Electrical hazards can include, but are not limited to, direct contact with live parts, fault conditions or stored charges.
Thermal hazards resulting in burns or radiation should also be considered. (The mechanical, electrical and thermal hazards mentioned above are not the only ones. They are simply food for thought while scrutinizing potential hazards to workers.)
• Assess each hazard and assign a level of risk. This is determined by acknowledging the expected severity of the injury and probability of occurrence. The severity of a potential injury is based on a worker’s direct and/or indirect contact with the hazard. In most cases, the severity pertains to the degree of harm to a person, but the risk process can also be applied to assess potential harm to other workers, equipment or the environment. It is important to note that the CSA methodology defines potential injuries as “slight” or “serious.” ISO 14121 uses the same terminology, but has an additional category: “death.”
To determine the probability of occurrence, the following factors must be taken into account:
• Frequency and duration of exposure to a hazard. This factor will vary based on the worker’s job function. Review who (i.e. maintenance workers, operators, etc.) and how many workers will be exposed to the hazard, the duration of the exposure, and how often it will occur. It is important to note that a hazard can be high risk even if the frequency of exposure is low and the duration is short.
• Hazard avoidability. If statistical data or accident history on a certain piece of equipment is available, it is easier to determine the probability of an injury occurrence.
This, in turn, will help to determine a worker’s likelihood of avoiding the hazard. Companies should record all incidents (accidents and near misses) for a given machine.
However, in cases where incidents are not logged, judgment is used to determine avoidability.
Keep in mind that the absence of incidents does not mean hazards satisfies CSA requirements. Once safeguarding methods have been chosen, conduct the risk estimation again and evaluate the hazards using the proposed safeguards to validate their effectiveness. If the risk has been reduced to a level deemed acceptable by the firm, apply the safeguards and move on to the next hazard.
The advantages of implementing a risk assessment system are well-documented. Having appropriate safeguards is a legal requirement and a fundamental component of good engineering practise. Most importantly, it is a critical part of maintaining a safe work environment.
Michael Wilson is a machine guarding specialist with the Industrial Accident Prevention Association (IAPA).