Often, clearing jams, making settings and cleaning operations are mistaken for maintenance activities that require lockout. But this is not the most productive or necessary way to operate a machine.
BY SIMON FRIDLYAND
Preventing access to moving parts is regulated, in Ontario, by the provincial Occupational Health and Safety Act, and throughout Canada by machine guarding standards. There is no choice in this matter; it is something that must be done.
However, if machine guarding is applied incorrectly, it can create a serious health and safety issue for the machine operators, as well as a serious productivity issue. One can easily erect a box around a machine so there is no access to moving or rotating parts, and then the machine will be safeguarded. However, the guarding would not last long, because there is always jam clearing to be done, adjustments to be made, and so on. Soon, such a box would likely be removed and workers would then be exposed to the machine’s dangerous motions and actions.
Before any type of guarding is considered, a risk assessment needs to be carried out to establish what the hazards are, how frequently a person will be exposed to those hazards, and what the likelihood is and what the severity of an injury could be. It is, of course, important that the risk assessment be documented. A proper Pre-Start Health and Safety Review (PSR) must have a risk assessment as part of the review.
As a rule of thumb, if fixed guards need to be removed more than once per week — even for machinery maintenance or cleaning — interlocking should be considered. Interlocked guards will cause the machine to stop if the guards are opened; alternatively, the guard cannot be opened until power to the machine has been removed.
For low-risk applications, it is acceptable to use an interlock with a single actuator on the guard and a single control channel with monitoring, but higher-risk applications need two independent actuators with separate control channels and cross-monitoring so that, should one switch or channel fail, the other will operate as it should.
If part of a machine takes a relatively long time to come to rest, a time-delay relay should be incorporated so that the guard will remain locked until the machine has come to rest.
A common misconception about guarding a machine is that the main issue is to keep operators away from the hazards. However, it is vital to ensure that the full operational, cleaning and maintenance needs of the machine are considered.
Let’s look at jam-clearing situations. Sometimes entry into a machine to clear a jam or do set-up while it is running is essential. If the system allows the operator to be in control of the machine at all times, then such an entry is possible. The CSA Z432-04 Standard for Safeguarding of Machinery describes the following:
Clause 188.8.131.52.12.1 allows certain operations (i.e. setting, process changeover, fault-finding) to be performed, if required, with the guard/door open and the protective device neutralized.
This requires the use of a manual control mode that simultaneously disables the automatic control mode; permits operation of the hazardous element only by triggering an enabling device, a hold-to-run control device, or a two-hand control device; and permits operation of the hazardous elements only in enhanced safety conditions (e.g. reduced speed, reduced energy/force, step-by-step).
Enabling devices are controls that may allow an operator to enter a hazardous area with the hazard running, only while the operator is holding the enabling device in the actuated position.
Enabling devices use either two- or three-position types of switches. Two-position types are off when the actuator is not operated, and are on when the actuator is operated. Three-position switches are off when not actuated (position 1), on when held in the centre (position 2) and off when the actuator is operated past the mid-position (position 3). In addition, when returning from position 3 to 1, the output circuit must not close when passing through position 2. This concept is shown in Figure 1.
Enabling devices must be used in conjunction with other safety-related functions. A typical example is running the machine in a controlled slow mode. Once in slow mode, an operator can enter the hazardous area holding the enabling device.
Clearing jams, setting, process changeovers and fault-finding are considered to be normal operational activities and are not classified as maintenance activities. Standards require that maintenance activities shall follow strict lockout procedures. All sources of energy (electrical, mechanical, hydraulic, and any other source of energy) shall be locked out or dissipated and the system shall be brought to a zero-energy state.
Lockout/tagout provisions and procedures as per the CSA Z460-05 Standard, Control of Hazardous Energy — Lockout and Other Methods, are required to be in place and communicated to staff.
Often, clearing jams, making settings and so on are mistaken for maintenance activities which require lockout. Once the lockout is implemented and the machine is brought to a zero-energy state, the power is lost to the controller and all coordinates and settings are lost. When the machine starts again, it may take a while to bring it back to the position it was in before a lockout. It is definitely not the most productive or necessary way to operate the machine.
Using appropriate controls based on a hazard assessment allows a safe and efficient way for clearing jams, and doing set-up work and cleaning operations.
Simon Fridlyand, P.Eng., is president of S.A.F.E. Engineering Inc., a Toronto-based company specializing in industrial health and safety issues and PSR compliance. He can be reached 416-447-9757 or email@example.com. For more information, visit www.safeengineering.ca.