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SEMI S2-0703a E © SEMI 1991, 2004 13 12 Emergency Shutdown 12.1 The eq uipment sh ould have an “emergenc y off” (EMO) circuit. The EMO actuato r (e.g., button), when activated, should place the equipment into a sa fe shu…

SEMI S2-0703a

11.4 Upon activation, the safety interlock should alert

the operator immediately.

EXCEPTION: Alerting the operator is not expected if a

safety interlock triggers the EMO circuit (see Section

12) or otherwise removes power to the user interface.

NOTE 24: An explanation of the cause is preferred upon

activation of a safety interlock.

11.5 Safety interlock systems should be fault-tolerant

and designed so that the functions or set points of the

system components cannot be altered without

disassembling, physically modifying, or damaging the

device or component.

EXCEPTION: When safety interlock systems having

adjustable set points or trip functions are used, access

should be limited to maintenance or service personnel

by requiring a deliberate action, such as using a tool or

special keypad sequences, to access the adjustable

devices or to adjust the devices.

NOTE 25: This section does not address the defeatability of

safety interlocks. See Section 11.7 for additional information.

NOTICE: Section 11.6 below will be withdrawn

upon July 1, 2006 publication and replaced by the

new Section 11.6 including: figures and tables as

shown in Delayed Revisions Section 2. The EH&S

Committee has voted that implementation of the

information is OPTIONAL before the effective date.

11.6 Electromechanical devices and components are

preferred. Solid-state devices and 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, and jarring.

EXCEPTION: Where the severity of a reasonably

foreseeable mishap is deemed to be Minor per SEMI

S10, a software-based interlock may be considered

suitable.

NOTE 26: Where a safety interlock is provided to safeguard

personnel from a Severe or Catastrophic mishap as

categorized by SEMI S10, consideration of positive-opening

type switches is recommended.

NOTE 27: Evaluation for suitability for use may also include

reliability, self-monitoring, and redundancy as addressed

under standards such as NEMA ICS 1.1 and UL 991.

NOTE 28: Solid-state devices include operational amplifiers,

transistors, and integrated circuits.

11.6.1 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.

NOTE 29: Paragraph 13.4.3 states additional assessment

criteria for safety-related components and assemblies.

NOTE 30: A FECS is a subsystem of a (PES) Programmable

Electronic System. IEC 61508 is the preferred standard for

complex PES.

NOTE 31: Related Information 14 provides additional

information on applications of FECS design.

11.7 The safety interlock system should be designed to

minimize the need to override safety interlocks during

maintenance activities.

11.7.1 Safety interlocks that safeguard personnel

during operator tasks should not be defeatable without

the use of a tool.

11.7.2 When maintenance access is necessary to areas

protected by interlocks, defeatable safety interlocks

may be used, provided that they require an intentional

operation to bypass.

11.7.2.1 Upon exiting or completing the maintenance

mode, all safety interlocks should be automatically

restored.

11.7.2.2 If a safety interlock is defeated, the

maintenance manual should identify administrative

controls to safeguard personnel or to minimize the

hazard.

11.8 The restoration of a safety interlock should not

initiate equipment operation or parts movement where

this can give rise to a hazardous condition.

11.9 Switches and other control device contacts should

be connected to the ungrounded side of the circuit so

that a short circuit to ground does not result in the

interlocks being satisfied.

11.10 Where a hazard to personnel is controlled

through the use of an enclosure, the enclosure should

either: require a tool to gain access and be labeled

regarding the hazard against which it protects

personnel; or be interlocked. In addition to enclosures,

physical barriers at the point of hazard should be

included where inadvertent contact is likely.

NOTE 32: Where the removal of a cover exposes a hazard,

consider additional labels. See Section 10 for guidance.

SEMI S2-0703a

12 Emergency Shutdown

12.1 The equipment should have an “emergency off”

(EMO) circuit. The EMO actuator (e.g., button), when

activated, should place the equipment into a safe

shutdown condition, without generating any additional

hazard to personnel or the facility.

EXCEPTION 1: An EMO circuit is not needed for

equipment rated 2.4 kVA or less, where the hazards are

only electrical in nature, provided that the main

disconnect meets the accessibility provisions of Section

12.5.2 and that the effect of disconnecting the main

power supply is equivalent to activating an EMO

circuit.

EXCEPTION 2: Assemblies that are not intended to be

used as stand-alone equipment, but rather within an

overall integrated system, and that receive their power

from the user’s system, are not required to have an

emergency off circuit. The assembly’s installation

manual should provide clear instructions to the

equipment installer to connect the assembly to the

integrated system’s emergency off circuit.

NOTE 33: It is recommended that the emergency off

function not reduce the effectiveness of safety devices or of

devices with safety-related functions (e.g., magnetic chucks or

braking devices) necessary to bring the equipment to a safe

shutdown condition effectively.

NOTE 34: If a fire detection or suppression system is

provided with the equipment, see Section 14 for additional

information.

12.1.1 If the supplier provides an external EMO

interface on the equipment, the supplier should include

instructions for connecting to the interface.

12.2 Activation of the emergency off circuit should

deenergize all hazardous voltage and all power greater

than 240 volt-amps in the equipment beyond the main

power enclosure.

EXCEPTION 1: A non-hazardous voltage EMO circuit

(typically 24 volts) and its supply may remain

energized.

EXCEPTION 2: Safety related devices (e.g., smoke

detectors, gas/water leak detectors, pressure

measurement devices, etc.) may remain energized from

a non-hazardous power source.

EXCEPTION 3: A computer system performing

data/alarm logging and error recovery functions may

remain energized, provided that the energized

breaker(s), receptacle(s), and each energized conductor

termination are clearly labeled as remaining energized

after EMO activation. Hazardous energized parts that

remain energized after EMO activation should be

insulated or guarded to prevent inadvertent contact by

maintenance personnel.

EXCEPTION 4: Multiple units mounted separately

with no shared hazards and without interconnecting

circuits with hazardous voltages, energy levels or other

potentially hazardous conditions may have:

 separate sources of power and separate supply

circuit disconnect means if clearly identified, or

 separate EMO circuits, if they are clearly

identified.

12.2.1 The EMO circuit should not include features

that are intended to allow it to be defeated or bypassed.

12.2.2 The EMO circuit should consist of

electromechanical components.

EXCEPTION 1: Solid-state devices and components

may be used, provided the system or relevant parts of

the system are evaluated and found suitable for use.

The components should be evaluated and found suitable

considering abnormal conditions such as over voltage,

under voltage, power supply interruption, transient over

voltage, ramp voltage, electromagnetic susceptibility,

electrostatic discharge, thermal cycling, humidity, dust,

vibration and jarring. The final removal of power

should be accomplished by means of electromechanical

components.

EXCEPTION 2: FECS may be used provided the FECS

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. IEC 61508 and ISO 13849-1 (EN 954-

1) are examples of internationally recognized electronic

safety systems standards. The final removal of power

should be accomplished by means of electromechanical

components.

NOTE 35: Paragraph 13.4.3 states additional assessment

criteria for safety-related components and assemblies.

NOTE 36: A FECS is a subsystem of a (PES) Programmable

Electronic System. IEC 61508 is the preferred standard for

complex PES.

12.2.3 All EMO circuits should be fault-tolerant.

12.2.4 Resetting the EMO switch should not re-

energize circuits, equipment, or subassemblies.

12.2.5 The EMO circuit should shut down the

equipment by deenergizing rather than energizing

control components.

12.2.6 The EMO circuit should require manual

resetting so that power cannot be restored

automatically.

SEMI S2-0703a

12.3 The emergency off button should be red and

mushroom shaped. A yellow background for the EMO

should be provided.

NOTE 37: Non-lockable self-latching (i.e., twist- or pull-to-

release) EMO buttons may be required by regulations.

12.4 All emergency off buttons should be clearly

labeled as “EMO,” “Emergency Off,” or the equivalent

and should be clearly legible from the viewing location.

The label may appear on the button or on the yellow

background.

12.5 Emergency off buttons should be readily

accessible from operating and regularly scheduled

maintenance locations and appropriately sized to enable

activation by the heel of the palm.

12.5.1 Emergency off buttons should be located or

guarded to minimize accidental activation.

12.5.2 No operation or regularly scheduled

maintenance location should require more than 3 m (10

feet) travel to an EMO button.

12.5.3 The person actuating or inspecting the EMO

button should not be exposed to serious risks of tripping

or falling or of coming in contact with energized

electrical parts, moving machinery, surfaces or objects

operating at high temperatures, or other hazardous

equipment.

12.6 See Section 13.5 for additional EMO guidelines

when EMOs are used with UPSs.

13 Electrical Design

13.1 This section covers electrical and electronic

equipment that use hazardous voltages.

13.2 Types of Electrical Work — The following are the

four types of electrical work defined by this guideline:

Type 1 — Equipment is fully deenergized.

Type 2 — Equipment is energized. Energized circuits

are covered or insulated.

NOTE 38: Type 2 work includes tasks where the energized

circuits are or can be measured by placing probes through

suitable openings in the covers or insulators.

Type 3 — Equipment is energized. Energized circuits

are exposed and inadvertent contact with uninsulated

energized parts is possible. Potential exposures are no

greater than 30 volts rms, 42.4 volts peak, 60 volts dc or

240 volt-amps in dry locations.

Type 4 — Equipment is energized. Energized circuits

are exposed and inadvertent contact with uninsulated

energized parts is possible. Potential exposures are

greater than 30 volts rms, 42.4 volts peak, 60 volts dc,

or 240 volt-amps in dry locations. Potential exposures

to radio-frequency currents, whether induced or via

contact, exceed the limits in Table A5-1 of Appendix 5.

13.3 Energized Electrical Work — The supplier should

design the equipment to minimize the need to calibrate,

modify, repair, test, adjust, or maintain equipment

while it is energized, and to minimize work that must

be performed on components near exposed energized

circuits. The supplier should move as many tasks as

practical from category Type 4 to Types 1, 2, or 3.

Routine Type 4 tasks, excluding troubleshooting,

should have specific written instructions in the

maintenance manuals. General safety procedures (e.g.,

wearing appropriate Personal Protective Equipment and

establishing barriers) for troubleshooting, including

Type 4 work, should be provided.

13.4 Electrical Design — Equipment should conform

to the appropriate international, regional, national or

industry product safety requirements.

13.4.1 Nonconductive or grounded conductive physical

barriers should be provided:

 Where it is necessary to reach over, under, or

around, or in close proximity to hazards.

 Where dropped objects could cause shorts or

arcing.

 Where failure of liquid fittings from any part of the

equipment would result in the introduction of

liquid into electrical parts.

 Over the line side of the main disconnect.

 Where maintenance or service tasks on equipment

in dry locations are likely to allow inadvertent

contact with uninsulated energized parts containing

either: potentials greater than 30 volts rms, 42.4

volts peak, or 60 volts dc; or power greater than

240 volt-amps.

NOTE 39: A dry location can be considered to be one that is

not normally subject to dampness or wetness.

NOTE 40: Removable nonconductive and noncombustible

covers are preferred.

13.4.2 Where test probe openings are provided in

barriers, the barriers should be located, and the probe

openings should be sized, to prevent inadvertent contact

with adjacent energized parts, including the energized

parts of the test probes.

13.4.3 Where failure of components and assemblies

could result in a risk of electric shock, fire, or personal

injury, those components and assemblies should be

certified by an accredited testing laboratory and used in

accordance with the manufacturer’s specifications, or

otherwise evaluated to the applicable standard(s).