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SEMI S14-0704 © SEMI 2000, 2004 5 which do not participate chemically in the process (e.g., vacuum pum p oil). 6.2.3.2 In assessing t h e risk, the evaluator should consider: • th e quantity, concentration , state, tempe…
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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
SEMI S14-0704 © SEMI 2000, 2004 6
Appendix 1 should be included. For each identified
residual risk, the report should:
• explain the mechanism of loss or damage;
• identify aggravating or necessary contributing
factors;
• identify the mitigating factors;
• state the assigned Severity for each type of loss and
present the rationale for its assignment. A “type”
is a column in Table A1-1, e.g., “Equipment
Physical Damage”;
• state the assigned Likelihood and present the
rationale for its assignment; and
• state the resulting Risk category.
NOTE 18: Criteria for risks may be found in Appendix 1,
Sections A1-2.5 through A1-2.8.
6.5.3.2 This report should also describe the fire risk
mitigation techniques included in the equipment design.
6.5.3.3 The final fire risk assessment report should be
prepared or reviewed by a party qualified, as described
in SEMI S7, to do such work.
NOTE 19: This party may be an employee of the equipment
supplier or may be a third party.
6.5.3.4 When this guideline is being used as part of a
SEMI S2 equipment evaluation, the manufacturer
should make the final fire risk assessment report avail-
able to the party performing the SEMI S2 evaluation.
6.5.3.5 The equipment supplier may make the final fire
risk assessment report available to other parties.
6.5.4 Summary Report
6.5.4.1 The summary report should be prepared from
the final fire risk assessment report and contain:
• a list of the residual fire risks and their ratings, and
• brief descriptions of the fire risk mitigation
techniques included in the equipment.
6.5.4.2 The equipment supplier should provide the
summary report to users of the equipment and may
provide it to other parties.
7 Fire Risk Mitigation
7.1 Overview
7.1.1 This section describes several means of
mitigating the risks of fire. It describes ways in which
the equipment and its use can be designed to minimize
the risks.
NOTE 20: The description of a mitigation technique in this
section is not intended to imply that such technique should be
used for each system. Therefore, the decision to include a
particular mitigation technique should be based on the
assessed risk.
NOTE 21: Fire detection and suppression are also means of
mitigating fire risk. The criteria for fire detection and
suppression systems are in SEMI S2.
7.1.2 In mitigating risks, the general hierarchy of
elimination, engineering controls, administrative
controls, warning and work practices should be
followed. Following this hierarchy comprises using
techniques which are highest in it if several techniques
are equally applicable. Design and use constraints, as
well as relative cost, however, may justify using
techniques from generally less preferable categories. In
any case, the residual risk should be assessed and
reported.
7.2 Fuels
7.2.1 Materials of Construction
7.2.1.1 The lowest fire risk is posed by noncombustible
materials of construction. Available noncombustible
materials are not, however, suitable or desirable for all
applications within semiconductor manufacturing
equipment.
NOTE 22: The properties necessary to perform the intended
function of system components and the properties necessary
to satisfy component-level standards may also restrict the use
of noncombustible materials.
7.2.1.2 When materials which are combustible are
chosen, the fire risk may be mitigated by:
• selecting those materials with the least undesirable
properties as described above; and
• minimizing the total mass and distribution of such
materials.
7.2.2 Process Chemicals
7.2.2.1 It may be possible to reduce the fire risk by
changing the quantities and species of the chemicals
used in the intended processes.
7.2.3 The fire risks of combustible materials of
construction and flammable and combustible process
chemicals may also be reduced by limiting those factors
described in Section 6.
7.3 Sources of Ignition
7.3.1 Potential sources of ignition should be considered
in conjunction with the fuels and oxidizers they might
ignite.
7.3.2 Risks due to sources of ignition can be mitigated
by:
• limiting their number,