In the process of adjustment, cleaning, maintenance and repair of mechanical equipment, the accidental start of equipment due to various reasons is one of the most typical accident causes.

1785-L60L/D Many companies may also be struggling with how to effectively control unexpected starts during maintenance.

ISO 14118:2017 Safety of machinery – Prevention of unexpected start-up (equivalent to GB/T 19670) was developed in order to effectively control the hazards caused by unexpected start-up.

Trident to prevent accidental activation

1785-L60L/D According to the results of the risk assessment, the following three measures can effectively prevent accidental start-up:

1. Manually isolate and dissipate energy sources, the machine shall be equipped with manually operated devices to isolate and dissipate energy supplies.

2. If the use of manual isolation and energy dissipation is not suitable for frequent short time intervention, the designer should provide additional automatic control functions to prevent accidental start-up.

3. Audible and/or visible warning signals and delayed start should be provided when risk assessment requires.

Automatic control function to prevent accidental start of the “five times the day”

For the use of automatic control function to prevent accidental start, the ISO14118 standard has been refined into five different levels, the letter (A→E), the farther back the position, the better the protection effect:

•Level A prevents accidental startup by stopping control. Such as the use of locked-position knobs, key switches, lockable mode selection switches, buttons with covers to prevent the accidental triggering of the start signal.
1785-L60L/D Level B/C prevents accidental start-up by giving a stop signal (Level B) or cutting off the energy source (Level C) through control signals automatically given by the machine, such as interlock switches on safety doors.
•Level D detaches the power transmission components from the machine’s power mechanism by mechanical means, such as a clutch, to prevent accidental starting.
•Level E prevents accidental initiation of dangerous movements by wedges, supports, and latches. The mechanical strength of the mechanical restraint device shall be sufficient to withstand the expected pressure. An example of preventing accidental start-up by locking the cylinder is shown.

After the control measures have been completed, verification is also an essential part of the process to help users check whether the control measures have been put in place.
• Isolation from any power supply shall be visible (visible break of the power supply circuit) or indicated by a clear and reliable indication of the effectiveness of the isolation function.
• Confirmation of energy dissipation can be made by means of built-in devices (such as pressure gauges) or test points to verify that there is no energy left in the internal/external parts of the machine and that maintenance operations can begin.

1785-L60L/D “Killer card” to prevent accidental start-up

If, according to the results of the risk assessment, other measures to prevent accidental start-up are not feasible, the stop state can also be monitored through the Type 2 stop device defined in IEC60204-1. If the static monitoring function detects movement, it should initiate a stop of class 0.

However, it is important to note that the parts of the control system that perform the static detection function should be designed to be safety relevant.