Page 73 - Electric Drives and Electromechanical Systems

66 Electric Drives and Electromechanical Systems

Ejection hazards, where material or a loose component is thrown from the
machine.
Noise and vibration hazards, which can cause loss of hearing, a loss of tactile
sense, or fatigue. In addition, an unexpected sound may cause a person to respond
in a startled manner.
Sudden release of stored energy from mechanical springs, capacitors, or pressur-
ised gas containers.
Environmental and biological hazards associated with a design, its manufacture,
operation, repair, and disposal.
Within any form of risk assessment, the first step is to identify the hazards, namely
those with the potential for causing harm. It should be noted that some physical hazards
might be present for the complete life cycle of the system whilst others may exist only
during the installation, or during maintenance. The second step is to identify the
possible accidents or failure modes associated with each hazard, or combinations of
hazards, that could lead to the release of the hazard potential and then to determine
the times in the life cycle at which such events could occur. To be successful in finding
the majority of these events requires the use of a systematic approach, such as a hazard
and operability study.
Accidents, however, do not just happen and the third step is to study the possible range of
triggering mechanisms, or conditions, which can give rise to each failure or accident. For
some events a combination or sequence of triggering conditions will be needed, in other
cases only one. The underlying causes, or the conditions which initiate the trigger, often
relate back to earlier phases of the project, for example to the design or planning stages.
Risk assessment is the estimation of the probabilities or likelihoods that the necessary
sequence of triggering events will occur for each particular hazard potential to be
released, and an estimation of the consequences of each accident or failure. The latter
may involve fatalities, serious injuries, long term health problems, environmental
pollution and financial losses. Risk management is an extension of risk assessment and
typically it involves the steps described above, together with the introduction of
preventative measures. The measures may be designed to reduce or eliminate the
hazards themselves, the triggering conditions, or on the magnitude of the potential
consequences.
This section describes the development of a practical risk assessment methodology,
as part of risk management of engineering systems; in particular how the process is
undertaken. It is clear that the risk assessment methodology should satisfy a number of
basic requirements, as shown in Fig. 2.16. The approach should be capable of:
Identifying significant hazards at various stages in the equipment’s life cycle.
Identifying the failure mechanisms that could lead to a release of each hazard’s
potential and the associated triggering conditions.
Assessing the nature and severity of the consequences of each type of physical
failure and other undesired events.