5.7.1 Measures for protection against failure of energy supply
If uncontrolled motion (especially inclined conveyors) may occur, conveyors shall be fitted with a means to stop and prevent further motion, which shall operate whenever the energy supply fails, e.g. a brake or other similar device.
5.7.2 Measures for protection against hazards arising from failure or malfunction of safety related parts of control systems
5.7.2.1 Controls and control systems
Controls and circuits used for safety purposes include :
trip device related circuits ;
ultimate-position switch related circuits ;
slack-rope switch related circuits ;
"interlocking" switches related circuits ;
emergency stop device related circuits ;
safety gear related circuits ;
brake related circuits ;
start and stop related circuits.
Licensed Copy: Wang Bin, ISO/EXCHANGE CHINA STANDARDS, 15/06/2011 03:59, Uncontrolled Copy, (c) BSI
5.7.2.2 Safety devices
Safety devices, (e.g. trip devices, ultimate-position switches, slack-rope switches, governors, interlocking switches, emergency stop devices), shall be designed, selected, located, and/or protected to meet intended site conditions, and the various applications of the equipment. e.g. ice build-up.
The switching arrangements of mechanically actuated electrical safety devices listed under 5.7.2.1, shall be of positive opening operation in accordance with EN 60947-5-1:1997, clause 3. (i.e. "safety switches").
If a safety device is actuated, a stop command shall be automatically given, which shall initiate a category "0" or category "1" stop, as appropriate, to be compatible with the design (see EN 60204-1:1997, 9.2.2.). The stop function shall comply with EN 954-1:1996, 5.2.
5.7.2.3 Transmission elements used for safety purposes
Transmission elements which are used for safety purposes, e.g. wiring, shall be designed so that in the event of failure or rupture, the equipment shall not fail to danger, i.e. a stop command shall be automatically given. For safety related parts of control systems see 5.7.2.5.
5.7.2.4 Response elements used for safety purposes
Response elements which are used for safety purposes, include safety related contactors, brakes, safety gear.
5.7.2.5 Control systems
The control system and control equipment shall be designed using proven techniques and shall use proven components (see EN 60204-1:1997, 9.4). The safety related parts of the control system shall be designed in accordance with the requirements of at least EN 954-1 Category 1 (see EN 954-1:1996, 6.2.2). Where programmable electronic equipment, or electronic devices including electronic sub-assemblies are used for safety related purposes, they shall be in accordance with the requirements of at least EN 954-1 Category 2 (see EN 954-1:1996, 6.2.3). Where programmable electronic equipment or electronic devices (including electronic sub- assemblies) are the only means used to transmit emergency stop commands, the emergency stop system shall be in accordance with the requirements of EN 954-1 Category 4 (see EN 954-1:1996, 6.2.5).
When the supply is switched-on there shall be no movement of the machinery.
In the event of a supply interruption, excessive supply fluctuation and restoration of supply (see EN 60204-1:1997, 7.5) or a fault or a failure of the control system, no dangerous situation shall occur (e.g. failure to stop, unexpected start-up) (see EN 954-1:1996, 4.2).
Electronic control circuitry, software, adjustable safety devices and adjustable safety equipment shall not be accessible to unauthorised persons, (e.g. by use of access codes, special tools).
5.7.2.6 Start function
Start devices shall be constructed and mounted so as to minimise the risk of inadvertent operation. They shall be positioned within reach of the operator and shall be clearly identifiable and visible (for positioning see 5.6.1 above).
If starting mechanical handling equipment may result in a hazardous condition, then a 3 s long unambiguous auditory warning shall be given 10 s before the start and/or a visual warning signal, such as a flashing lamp, shall be provided in accordance with EN 457:1992, EN 842:1996 and EN 61310-1:1995, as appropriate. Such signals shall be provided for example, in situations where mechanical handling equipment is out of sight of the operator, or when it is necessary to warn persons who may be in the working or traffic areas, that a particular conveyor or mechanism is about to start.
Where a conveyor is arranged to feed onto other conveyors, starting shall be co-ordinated by the use of suitable interlocks. Suitable interlocks shall ensure correct sequential starting and prevent conveyors being fed which are not in operation or which are already operating fully loaded.
Licensed Copy: Wang Bin, ISO/EXCHANGE CHINA STANDARDS, 15/06/2011 03:59, Uncontrolled Copy, (c) BSI
5.7.2.7 Stop function
Stop devices shall be positioned within reach of the operator at all control stations and shall be clearly identifiable and visible (for positioning see 5.6.1 above). The stop function shall be a category “0” or category “1” stop, as appropriate, to be compatible with the design (see EN 60204-1:1997, 9.2.2).
Stop devices shall be of the impulse type and after actuation of a stop device the appropriate conveyor, or if required, the conveyor system, shall come to a halt and then remain in a stationary condition.
The stop function shall be arranged to avoid creating hazardous conditions (e.g. dangerous discharge of conveyed material). If the stopping of particular conveyors could cause hazards at other related parts of the installation, stopping shall be suitably controlled (e.g. by time delay or sequencing). Stopping shall be accompanied by an unambiguous visual and/or acoustic warning (See EN 457:1992, EN 842:1996 and EN 61310-1:1995).
5.7.2.8 Emergency stop system
The emergency stop system shall be in accordance with EN 954-1:1996, 5.3, and EN 418:1992 and shall be a category “0” stop or category “1” stop, as appropriate, to be compatible with the design (see EN 418:1992, 4.1.5).
An emergency stop shall also be accompanied by an unambiguous visual and/or acoustic warning in accordance with EN 457:1992, EN 842:1996 and EN 61310-1:1995, as appropriate.
Emergency stop devices shall have positive operation, be self-latching and shall be either:
a) one or more push button operated switches which shall be installed in such a way that at least one may be reached within 10 m from any accessible point of the equipment ; and or
b) one or more pull cord operated switches arranged along the full length of the installation ; or
c) the conveyor’s supply disconnecting device if the distance from any accessible point of the equipment to the disconnecting device is 10 m or less.
Emergency stop devices shall be at all control stations, working positions and at accessible parts of the machinery including loading points, unloading points, walkways and transfer points (for positioning see 5.6.1 above).
When an emergency stop device(s) has been actuated and the conveyor has come to a halt, the conveyor shall remain in a stationary condition until that device has been reset and the start device has subsequently been actuated. Where more than one emergency stop device is provided, means shall be incorporated to show which device has been actuated.
The initiation of the emergency stop function shall not create a hazardous condition, e.g. dangerous discharge of conveyed material.
The height of the emergency stop device shall be between 0,6 m and 1,7 m from the surface on which the operator stands.
NOTE The provision of an emergency stop device is not an alternative to the installation of suitable guarding, see EN 418:1992, 4.1.3.
5.7.2.9 Pull-cord operated emergency stop switch
The arrangement of pull-cord operated emergency stop switches shall be such that their associated switching device(s) will operate if the operating cord is pulled in any direction or if the cord breaks. Pull-cord switches shall also be designed so that the operating failure of any one spring will cause its associated switching device(s) to operate (i.e. not cause a failure to danger).
The pull cord stop switch shall be actuated by the application of a horizontal force to the pull-cord of less than 125 N, at a point midway between two support rings and perpendicular to the cord. The sideways cord movement (between the rest position and the actuation position) shall be less than 300 mm.
Licensed Copy: Wang Bin, ISO/EXCHANGE CHINA STANDARDS, 15/06/2011 03:59, Uncontrolled Copy, (c) BSI
Only cords which are free from kinks and of a type unlikely to kink in service, shall be selected for use. The maximum length and other details shall be in accordance with the pull cord switch supplier’s recommendations (e.g. protection of support rings and pulleys, prevention of freezing, changes in length due to temperature changes, etc.).
5.7.2.10 Restarting after an emergency stop
Following an emergency stop, restarting shall be in accordance with 5.7.2.6 and EN 418:1992, 4.1.11 and 4.1.12.
5.7.2.11 Automatic malfunction detection
Where appropriate, the following automatic malfunction detection devices shall be installed which shall be constructed and mounted so as to minimise the risk of inadvertent operation:
a) belt misalignment detection devices ;
b) conveyor, chute, hopper, blockage / overload detection devices ; c) shaft rotation sensing devices ;
d) belt underspeed sensing devices ; e) heat sensing devices ;
f) height and/or width sensing devices.
If a hazardous condition is detected, an unambiguous acoustic and/or visual warning signal shall be provided to the conveyor operator in accordance with EN 457:1992, EN 842:1996, EN 61310-1:1995 as appropriate, or alternatively, in extreme circumstances a stop may be automatically initiated. In particular circumstances, linked supplying conveyors may be automatically slowed - down, or stopped in a suitably controlled manner.