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SEMI S14-0704 © SEMI 2000, 2004 4 intended to be used in a poten tially explosive atmosphere, the certification to IEC 60950 would not sufficiently control its risk of being a source of ignition. 6.1.5 Th e consequences …
SEMI S14-0704 © SEMI 2000, 2004 3
5.1.7 hazard — a condition that is a prerequisite to a
mishap.
5.1.8 hazardous voltage — unless otherwise defined by
an appropriate international standard applicable to the
equipment, voltages greater than 30 volts rms, 42.4
volts peak, 60 volts dc are defined in this document as
hazardous voltage.
NOTE 6: The specified levels are based on normal conditions
in a dry location environment.
5.1.9 ignition energy — sufficient energy to ignite a
combustible material. The energy required depends on
the form of the energy and the composition and form of
the combustible material.
NOTE 7: The combustible material may be solid, liquid, or
gas.
5.1.10 likelihood — the expected frequency with which
a mishap will occur. Usually expressed as a rate (e.g.,
events per year, per product, per wafer processed).
5.1.11 mishap — an unplanned event or series of
events that results in death, injury, occupational illness,
damage to or loss of equipment or property, or
environmental damage.
5.1.12 noncombustible material — a material that, in
the form in which it is used and under the conditions
anticipated, will not ignite, burn, support combustion,
or release flammable vapors when subjected to fire or
heat. Typical noncombustible materials are metals,
ceramics, and silica materials (e.g., glass and quartz).
5.1.13 process chemicals — solids, liquids, and gases
used in the normal use of the equipment included in the
scope of this document.
NOTE 8: Solids, liquids, and gases used in the maintenance
procedures (e.g., isopropanol used as a cleaning agent)
specified by the equipment supplier should be considered as
well as those used in operation.
5.1.14 pyrophoric material — a chemical that will
spontaneously ignite in air at or below a temperature of
54.4° C (130° F).
5.1.15 residual risk — that risk which remains after
engineering, administrative, and work practice controls
have been implemented.
5.1.16 risk — the expected losses from a mishap,
expressed in terms of severity and likelihood.
5.1.17 safe shutdown condition — a condition in which
all hazardous energy sources are removed and
hazardous production materials are removed or
contained, unless this results in additional hazardous
conditions.
5.1.18 semiconductor manufacturing process — those
manufacturing steps which are part of the creation of
active or passive electrical devices on a semiconducting
wafer, including the deposition of passivation layers
after final metallization, but excluding testing and
dicing.
5.1.19 severity — the extent of the worst credible loss
from a mishap caused by a specific hazard.
5.1.20 supervisory alarm — an alarm indicating a
supervisory condition.
5.1.21 supervisory condition — a condition in which
action or maintenance is needed to restore or continue
proper function.
5.1.22 trouble alarm — an alarm indicating a trouble
condition.
5.1.23 trouble condition — a condition in which there
is a fault in a system, subsystem or component that may
interfere with proper function.
6 Fire Risk Assessment
6.1 Overview
6.1.1 This section provides criteria for evaluation of
the risks associated with several types of fire hazards.
6.1.2 For each identified hazard described in Section 6,
the evaluator should analyze the contributing, causal,
and mitigating factors. The evaluator should also
review any assessment of the material, component, or
equipment as a whole by an accredited testing
laboratory.
6.1.3 The risk assessment should include both normal
operation and the consequence of reasonably foresee-
able, single-point failures within the equipment. It
should not include exposure to fire or external ignition
sources not within the intended use environment.
6.1.4 Certifications by an accredited testing laboratory
of materials, components, or the equipment as a whole
may be used in the fire risk assessment. However, such
certifications are valid only to the extent that the
conditions of use for the certification correlate to the
conditions of use for the equipment whose fire risk is
being assessed.
NOTE 9: For example, a personal computer certified to IEC
60950 might be incorporated into equipment for use as a
controller. The material flammability requirements of IEC
60950 may or may not be sufficient for this use of the
personal computer, depending upon its exposure to oxidizers
and external sources of ignition when incorporated into the
equipment. Also, the levels of smoke tolerable in the
environment for which a general industry standard was
written may exceed those tolerable in semiconductor
manufacturing cleanrooms. Furthermore, if the equipment is
SEMI S14-0704 © SEMI 2000, 2004 4
intended to be used in a potentially explosive atmosphere, the
certification to IEC 60950 would not sufficiently control its
risk of being a source of ignition.
6.1.5 The consequences and the probability of fire
from each identified hazard should be assessed and
rated, as described in SEMI S10. See Appendix 1 for
the criteria used for the assignments of Severity,
Likelihood and Risk in this document.
6.1.5.1 The assigned Severity and Likelihood and
resulting Risk category should be recorded as part of
the analysis.
6.1.5.2 For those hazards for which the Risk depends
on the conditions of use or use environment, the
equipment supplier should make and state appropriate
assumptions. If the equipment supplier is unable to
make appropriate assumptions as to the Likelihood
because it depends predominantly on factors in the
users' sole control (e.g., adherence to specified
procedures), the supplier should state that and provide
an estimate of the Severity.
NOTE 10: The facilities requirements on which the risk
assessment depends are to be specified by the equipment
supplier.
6.1.6 For fire to occur, there must be a fuel, an oxidizer
and a source of ignition. Elimination of any of these
factors eliminates the risk of fire. Similarly, the
Severity, Likelihood and Risk of a fire can be reduced
by reducing one or more of these elements
appropriately.
6.1.7 It is important to remember that there are often
implicit oxidizers (e.g., room air) and sources of
ignition (e.g., room temperature for a pyrophoric
material).
6.1.8 The fire risk assessment should include the
judgement of a qualified (as described in SEMI S7)
party to determine the level of detail of the assessment.
That party may group similar hazards for assessment
and reporting.
NOTE 11: Such grouping could include, for example, all of
the knobs and buttons of similar materials into one group, the
heated surfaces into a second, and the several flammable
liquids with similar properties into a third.
6.2 Fuels
6.2.1 Fuels include all those materials capable of
reacting with an oxidizer in a fire. The risks of both the
materials of which the equipment is constructed and the
process chemicals used in it should be assessed.
6.2.2 Materials of Construction
6.2.2.1 The risk assessment should include all of the
materials of construction, regardless of quantity or
application.
NOTE 12: This includes small parts, such as knobs, buttons,
electrical contactors, terminal strips, circuit boards, signal
wire and power wiring as well as large components, modules
(such as mini-environments) and subassemblies.
NOTE 13: Some of the smallest components can create a
high risk, as in the potential for ignition by adiabatic
compression of fluoropolymer seats in high pressure oxygen
valves.
NOTE 14: The assessment can be simplified by grouping
similar items together. Example 1: wiring that has the same
type of insulation. Example 2: knobs, switches, handles and
latches made from similar polymers. Identified groups should
include their approximate total mass.
6.2.2.2 In assessing the risk, the evaluator should
consider:
• the size of each component,
• the total quantity and distribution of similar
components,
• the inherent properties of the material, such as
ignitability, flame spread, heat of combustion, and
byproducts (See Appendix 2 for guidance on
evaluation of these properties.),
• the exposure to oxidizers, and
• the exposure to ignition sources.
NOTE 15: The specification control of materials used in
approved electrical components should also be considered.
Approvals may allow for substitution of many materials with
equivalent flammability ratings.
NOTE 16: The inherent properties of materials affect two
types of risk within the equipment: flame spread risk and
contamination risk (i.e., smoke damage from combustion
byproducts). In the case of electrical and electronic
components used in assemblies and equipment that are
constructed and used in accordance with applicable standards
(e.g., IEC 61010-1, IEC 60204-1), flame spread risk may be
adequately controlled by the standard, and detailed
assessment of the material properties of such components that
affect flame spread may not be warranted. However, a
significant contamination risk could still remain (e.g., a
standard may allow a component mounted on a printed circuit
board to fail and burn, as long as the burning remains local to
the printed circuit board) and warrant a detailed assessment of
related material properties of the components. The level of
detail of the assessment may also be affected by the
mitigation method chosen (see Section 7).
6.2.3 Process Chemicals
6.2.3.1 This portion of the risk assessment should
include all of the process chemicals expected (based on
the equipment supplier' s recommended or baseline
processes) to be used in the equipment. It should also
include flammable and combustible wastes generated or
collected within the equipment and fluids in the
equipment which are required for its operation but
SEMI S14-0704 © SEMI 2000, 2004 5
which do not participate chemically in the process (e.g.,
vacuum pump oil).
6.2.3.2 In assessing the risk, the evaluator should
consider:
• the quantity, concentration, state, temperature, and
pressure of each chemical in each container,
• for those chemicals supplied automatically by the
facility, the available flow, pressure, and total
quantity,
• the aggregate supplies and distribution of similar
chemicals,
• the inherent properties of the chemicals, such as
flammable limits, flash point, autoignition
temperature, heat of combustion, and the products
of combustion and decomposition (see the Material
Safety Data Sheets for guidance on evaluation of
these properties),
• the exposure to oxidizers, and
• the exposure to ignition sources.
NOTE 17: Chemicals with similar fire properties may be
considered together for the purpose of this assessment.
6.3 Sources of Ignition
6.3.1 Sources of ignition can be broadly divided into
those within the equipment and those external to it.
6.3.2 Internal Sources
6.3.2.1 Potential electrical ignition sources:
• devices or conditions that in normal operation can
generate ignition energy (e.g., heaters, static
electricity, lasers);
• devices or conditions that in reasonably foreseeable
assembly, use and/or wear conditions can generate
ignition energy (e.g., power connectors, terminal
strips);
• devices that in reasonably foreseeable single point
failure modes can generate ignition energy (e.g.,
transformers, electronic components); and
• short circuits.
6.3.2.2 Potential chemical ignition sources:
• exothermic process chemical reactions,
• exothermic reactions from inadvertent mixing of
process chemicals,
• exothermic reactions between process chemicals
and materials of construction, and
• release of pyrophoric or air-reactive chemicals
from processing or maintenance.
6.3.2.3 Sudden changes in process conditions:
• rapid (sometimes called “adiabatic”) compression
of gas mixtures, and
• rapid increases in temperature.
6.3.2.4 Mechanical friction
6.3.3 External Sources
6.3.3.1 External sources include expected and foreseen
conditions of the equipment’s use. As these are factors
normally outside the control of the equipment supplier,
their risks are difficult to assess. They are outside the
scope of this document.
6.4 Oxidizers
6.4.1 The most common oxidizer is air, which is
present within and around most semiconductor
manufacturing equipment. Unless specific measures
are taken to exclude air (e.g., inert pressurizing of an
electrical enclosure), it should be assumed to be
available in infinite supply.
6.4.2 It is possible that some materials of construction
will act as oxidizers or will yield oxidizers when
subjected to heat.
6.4.3 Several common process chemicals (e.g., oxygen
and hydrogen peroxide) are oxidizers. Their risks
should be assessed in a manner similar to that described
above for process chemicals that are fuels.
6.5 Reporting
6.5.1 Although these guidelines are intended for use
throughout the design and development process, it is
not the intent of these guidelines that the equipment
supplier should make all of the information recorded
during the development of the equipment available to
others. The equipment supplier should document the
fire risk assessment and mitigation in three forms:
internal records, a final fire risk assessment report, and
a summary report.
6.5.2 Relevant analyses, assessments, and design
decisions should be documented in the equipment
supplier' s internal records. These records need not,
however, be made available to other parties.
6.5.3 Final Fire Risk Assessment Report
6.5.3.1 This report should contain an itemized list of
the residual risks identified in reviewing the final
design, considering the risks described in the preceding
subsections or otherwise known or foreseen by the
evaluator. Only those risks meeting the criteria in