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SEMI S22-1103a © SEMI 2003, 2005 22 13.7.3.1 FECS may be used in conju nction with electromechanical or solid state devices and co mponents provided the programmable safety control system conforms to an appropriate stan …
SEMI S22-1103a © SEMI 2003, 2005 21
13.4 Operating Modes When a system has more than one operating mode, and operating mode selection can
result in a hazardous condition, mode selection should be restricted to trained service or maintenance personnel.
13.5 Suspension of safeguards should satisfy ¶8.15.
13.6 Safety Controls
13.6.1 Hold-to-run Controls Hold-to-run controls should only be used if a hazard analysis determines that they
are an appropriate and adequate means to mitigate a hazard. When hold-to-run controls are used, they should
necessitate continuous actuation of the control devices to achieve operation.
13.6.2 Two Handed Controls When dual series-connected hand controls are used to isolate the operator from
hazards, the hand controls and/or control circuit should comply with the following:
a) the hand controls should be momentary contact switches with black or green heads. Each hand control should
be protected against unintended operation;
b) each hand control should be arranged by design, construction, and/or separation so that the use of both hands
is needed to start the machine cycle. Preferably, they are mounted at least 610 mm (24 in.) apart at the same
height;
c) two hand controls should be designed so that both hand controls need to be depressed within one second of
each other for the machine to cycle and both hand controls need to be held depressed until the hazard no
longer exists; and
d) the control system should incorporate an anti-repeat feature that limits the machine to one cycle for each
depression of the hand controls. The control system should incorporate an anti-tie-down feature that demands
the release of both hand controls between cycles.
13.6.3 Combined Start and Stop Controls Controls that alternately initiate and stop motion should only be used
when no hazardous condition can arise from their operation.
13.7 Safety Interlock Circuits
13.7.1 Protection against Fault Conditions When a single point failure can result in an unacceptable level of
risk, a safety interlocking circuit or other suitable means should be provided to protect against the consequences of
that single point failure.
13.7.2 Safety interlock Function Safety interlocks should be designed such that the equipment is automatically
brought to a safe condition before personnel can access the point of hazard. Each safety interlock, when activated,
should alert the operator immediately.
EXCEPTION: If a safety interlock triggers the emergency off (EMO) circuit, or otherwise removes power to the
user interface, notification to the operator is not needed.
NOTE 38: An explanation of the cause is preferred upon activation of a safety interlock.
NOTICE: ¶13.7.3 below will be withdrawn upon July 1, 2006 publication and replaced by the new ¶13.7.3
including: figures and tables as shown in Delayed Revisions §1, however, the EH & S Committee has voted
that implementation of the information is OPTIONAL before the effective date.
13.7.3 Safety Interlock Design Electromechanical devices and components are preferred. Solid state devices and
non-programmable solid state components may be used provided that the safety interlock system or relevant parts of
the system are evaluated for suitability for use in accordance with appropriate standard(s). The evaluation for
suitability should take into consideration abnormal conditions such as overvoltage, undervoltage, power supply
interruption, transient overvoltage, ramp voltage, electromagnetic susceptibility, electrostatic discharge, thermal
cycling, humidity, dust, vibration, jarring, or interfacing to a network.
NOTICE: ¶13.7.3.1 below will be withdrawn upon July 1, 2006 publication and replaced by the new ¶13.7.3.1
including: figures and tables as shown in Delayed Revisions §1, however, the EH & S Committee has voted
that implementation of the information is OPTIONAL before the effective date.
SEMI S22-1103a © SEMI 2003, 2005 22
13.7.3.1 FECS may be used in conjunction with electromechanical or solid state devices and components provided
the programmable safety control system conforms to an appropriate standard for electronic safety systems.
Components of the FECS should be tested and certified according to the requirements of the standard used.
Examples of recognized electronic safety systems standards include IEC 61508, ISO 13849-1, (EN 954-1),
ANSI/ISA SP84.01, DIN/V/VDE-0801.
EXCEPTION: Where the severity of a reasonably foreseeable mishap is deemed to be minor per SEMI S10, a
software-based safety interlock may be considered suitable.
NOTE 39: ¶8.4.1 states additional assessment criteria for safety-related components and assemblies.
NOTE 40: A FECS is a subsystem to a (PES) Programmable Electronic System. IEC 61508 is the preferred standard for
complex PES.
13.7.4 Safety Interlock Override The safety interlock system should be designed to minimize the need to
override safety interlocks during maintenance activities.
13.7.5 When maintenance access to areas protected by safety interlocks is necessary, safety interlocks that can be
defeated may be used, provided that they require an intentional operation to bypass. Safety interlocks that safeguard
operator tasks should not be able to be defeated without the use of a tool. Upon exiting or completing the
maintenance mode, all safety interlocks should be automatically restored.
13.7.6 If a safety interlock is defeated, the maintenance manual should identify administrative controls to safeguard
personnel and to minimize the hazard.
13.7.7 The restoration of a safety interlock should not automatically initiate machine motion or operation where this
can give rise to a hazardous condition.
13.7.8 Safety Interlock Circuit Connection To reduce the risk of interlocks not functioning correctly from short
circuiting of the device or wiring to ground, switches, contacts, and other safety interlock control devices should not
be connected to the earthed side of the circuit.
13.7.9 Shunt Trip Circuits Shunt trips should not be used as safety interlocks because they are not fail-safe.
13.8 Multiple Points of Control
13.8.1 Where multiple points of control are provided on a system, a hardware based device which meets the
considerations of ¶13.7 should be used to ensure a single point of control when multiple points of control can cause
an unacceptable risk.
13.8.2 The control point selection hardware-based device should either be lockable or be able to be under the
immediate control of the person(s) exposed to the hazard.
14 Interface Control
14.1 Hand Control Devices — Hand control devices should be located so that their intended use does not cause an
unacceptable risk.
14.1.1 Hand control devices should be designed and mounted to minimize inadvertent operation if an unacceptable
risk could result from inadvertent activation.
14.1.2 Control devices should withstand the stresses of normal use and foreseeable misuse. Considerations should
be given to normal operation as well as fault conditions. Factors such as chemical exposure to insulation, mechanical
and thermal stress, radiation, and other environmental factors that may result in unacceptable risks, should be taken
into account.
14.2 Push-actuators (buttons)
14.2.1 Colors — The color of the start/on actuator should be white, gray, black, or green. Green is preferred. Red
should not be used for the start/on actuator.
14.2.1.1 The color red should be used for EMO actuators. A yellow background for the EMO should be provided.
Refer to ¶13.3.
14.2.1.2 Non-EMO actuators should be differentiated from the EMO actuator.
SEMI S22-1103a © SEMI 2003, 2005 23
14.2.1.3 The colors for stop/off actuator should be red, black, gray or white. A red, non-mushroom shaped actuator
is preferred. Green should not be used for the stop/off actuator.
NOTE 41: NFPA 79 prefers that all pushbuttons for STOP or OFF functions be colored red, but will permit black, white, or
gray.
14.2.1.4 Contact push-actuators that cause operation while they are actuated and cease the operation when they are
released should be colored white, gray, or black. The colors red, yellow, and green should not be used.
14.2.1.5 Reset push-actuators should be colored blue, white, gray, or black. Reset push-actuators should not be
colored the same as stop/off actuators.
14.2.2 Markings All controls should be marked with their functional identification in accordance with Section
20.3.
14.3 Indicator Lights and Displays
14.3.1 Colors Indicator light lenses should be color-coded in accordance with Tables A1-8 through A1-10 in
Appendix 1.
14.3.2 Flashing Lights Flashing lights should be used when the application requires a compelling safety
indication to the operator. Single LED indicators should not be used for this application.
14.3.3 Illuminated Push-actuators Illuminated push-actuators should be color-coded in accordance with
Appendix 1 Tables A1-8 through A1-10. The color red for the emergency off actuator should not depend on the
illumination.
14.4 Actuators used to initiate a function should be designed and mounted to minimize inadvertent activation if an
unacceptable risk could result from that inadvertent activation.
14.5 Disconnects — All main disconnecting means should meet the considerations of ¶9.3.6. The means of energy
isolation for maintenance and servicing should be consistent with procedures described in the manuals.
15 Electrical Enclosures
15.1 Construction of Electrical Enclosures
15.1.1 Electrical enclosures should provide protection against contact with hazardous voltages as defined in Section
10 of this guideline.
15.1.2 Electrical enclosures should prevent the ingress of substances that may cause electrical faults within the
electrical enclosure. These substances may be emitted by the equipment under fault conditions or would be
expected in the equipment’s intended use environment.
NOTE 42: Facilities activation of sprinklers is not intended to be covered under this paragraph.
15.1.3 Electrical enclosures should have a complete bottom sufficient to prohibit the emission of molten material or
burning insulation under fault conditions.
NOTE 43: Baffling or equivalent construction techniques can be used to satisfy ¶15.1.1 through ¶15.1.3 and still meet the
functional needs of adequate ventilation.
15.1.4 Electrical enclosures should be of suitable substantial construction to withstand normal intended use and
reasonably foreseeable misuse. Enclosure walls and covers should have adequate strength to withstand deflection
that reduces electrical clearances below an acceptable value or prevent contact with energized parts. Enclosures
should be evaluated by inspection or testing in accordance with the enclosure test criteria in ¶22.14.
15.2 Access All panels providing access to electrical components should be located and mounted to facilitate:
a) accessibility and maintenance, and
b) protection against the external influences that may result in safety hazards.
NOTE 44: This section only applies to circuits that handle hazardous voltage or power.