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SEMI S14-0704 © SEMI 2000, 2004 19 R4-7.1.3 with a failure of two protective features (Category 1 only). NOTE R4-1: The equipment Categories are based on the intended conditions of use: Category 1: explosive atmospheres …
SEMI S14-0704 © SEMI 2000, 2004 18
R4-4.2 In relation to the occurrence of hazardous
explosive atmospheres, the origin of the potentially
explosive atmosphere should be described. This should
include:
R4-4.2.1 The safety data of the chemicals or gases
involved (Physical properties, including where
available: combustion properties, ignition requirements,
explosion behavior),
R4-4.2.2 How and where the chemicals and gases are
stored, handled and controlled,
R4-4.2.3 The degree of dispersion of the flammable
substance (e.g., gases, vapors, mists, dusts),
R4-4.2.4 The concentration of the flammable substance
in air within the explosion range, and
R4-4.2.5 The amount of explosive atmosphere
sufficient to cause injury or damage by ignition, and
any factors which limit the quantity or the amount that
is available to be ignited.
R4-4.3 The scenarios or conditions that result in the
explosive atmosphere should be described, indicating
the nature of the sequence of events that lead to the
explosion. This may include quantification of the
explosive atmosphere and/or results of the explosion.
R4-5 Hazard Identification – Ignition Sources
R4-5.1 The ignition sources present within or close to
the potentially explosive atmosphere should be
classified according to the likelihood of their
occurrence in the following manner:
R4-5.1.1 Sources of ignition which are assumed to be
present at all times, because the likelihood of
occurrence of an effective ignition source cannot be
estimated,
R4-5.1.2 Sources of ignition which can occur
continuously or frequently,
R4-5.1.3 Sources of ignition which can occur in rare
situations, and
R4-5.1.4 Sources of ignition which can occur in very
rare situations.
R4-5.2 All potential ignition sources should be
considered including:
R4-5.2.1 Sparks, flames, electric arcs, high surface
temperatures, acoustic energy, optical radiation,
electromagnetic waves,
R4-5.2.2 Electrostatic charges capable of resulting in
dangerous discharges,
R4-5.2.3 Stray electric and leakage currents in
conductive equipment parts, which could result in, for
example, the occurrence of dangerous corrosion,
overheating of surfaces or sparks capable of provoking
an ignition may need to be considered,
R4-5.2.4 Overheating caused by friction or impacts
occurring, for example, between materials and parts in
contact with each other while rotating or through the
intrusion of foreign bodies may need to be reduced, as
far as possible, at the design stage, and
R4-5.2.5 Adiabatic Compression: Equipment and
protective systems may need to be designed or fitted
with integrated measuring, control and regulation
devices so that pressure compensations arising from
them do not generate shock waves or compressions
resulting in ignition.
R4-5.2.6 Impact Energy
R4-5.2.7 Chemical Reactions: e.g., combination of
highly reactive chemicals producing sufficient energy
to ignite these chemicals, by-products or other
chemicals/articles in the vicinity.
R4-6 Mitigation Measures Implemented &
Protection Systems Integrated
R4-6.1 This section should describe in detail the
measures taken to mitigate the explosion risks that have
been identified, including those:
• to prevent the creation of explosive or ignitable
atmospheres, e.g., through the use of ventilation,
purging or inerting and the prevention of releases
etc.,
• to prevent the ignition of the atmosphere, e.g.,
through the use of appropriately rated electrical
equipment or relocating ignition sources outside
the classified zone,
• to limit the development or propagation of the
explosion, e.g., through the use of an explosion
suppression system, and
• to limit the damage caused by the explosion, e.g.,
through venting or barriers.
R4-7 Residual Risk
R4-7.1 The documentation should include a statement
of the residual explosion risk describing the expected
explosion scenario and summarizing the Residual
Explosion Risk that exists:
R4-7.1.1 with all protective features operating
(Category 1, 2 and 3),
R4-7.1.2 with a failure of one protective feature
(Category 1 & 2 only), and
SEMI S14-0704 © SEMI 2000, 2004 19
R4-7.1.3 with a failure of two protective features
(Category 1 only).
NOTE R4-1: The equipment Categories are based on the
intended conditions of use:
Category 1: explosive atmospheres are highly likely to occur
and are present continuously frequently or for long periods
Category 2: explosive atmospheres are likely to occur
Category 3: explosive atmospheres are less likely to occur
and, if they occur, do so infrequently and briefly
NOTICE: Paragraphs entitled “NOTE” are not an
official part of this safety guideline and are not intended
to modify or supersede the official safety guideline.
These have been supplied by the committee to enhance
the usage of the safety guideline.
SEMI makes no warranties or representations as to the
suitability of the guideline set forth herein for any
particular application. The determination of the
suitability of the guideline is solely the responsibility of
the user. Users are cautioned to refer to manufacturer’s
instructions, product labels, product data sheets, and
other relevant literature respecting any materials
mentioned herein. This guideline is subject to change
without notice.
The user’s attention is called to the possibility that
compliance with this guideline may require use of
copyrighted material or of an invention covered by
patent rights. By publication of this guideline, SEMI
takes no position respecting the validity of any patent
rights or copyrights asserted in connection with any
item mentioned in this guideline. Users of this guideline
are expressly advised that determination of any such
patent rights or copyrights, and the risk of infringement
of such rights, are entirely their own responsibility.
Copyright by SEMI® (Semiconductor Equipment and Materials
International), 3081 Zanker Road, San Jose, CA 95134. Reproduction o
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the contents in whole or in part is forbidden without express written
consent of SEMI.
SEMI S15-0200 © SEMI 20001
SEMI S15-0200
SAFETY GUIDELINE FOR THE EVALUATION OF TOXIC AND
FLAMMABLE GAS DETECTION SYSTEMS
This safety guideline was technically approved by the Global Environmental, Health, and Safety Committee
and is the direct responsibility of the North American Environmental, Health, and Safety Committee. Current
edition approved by the North American Regional Standards Committee on December 15, 1999. Initially
available on www.semi.org January 2000; to be published February 2000.
1 Purpose
1.1 This guideline provides consid erations for the
evaluation of fixed gas detection systems used to
monitor for safety of plant personnel, product and
materials, the local environment and community. It
provides an evaluation guide and reference sources
appropriate to facilities and equipment where toxic and
flammable gases are used and stored in gaseous or
liquid form.
2 Scope
2.1 This guideline applies to toxic and flammable gas
detection and addresses performance characteristics of
gas detection systems.
2.2 It also describes several techno logies available for
detection of such gases and their performance
characteristics.
2.3 This safety guideline does not purport to address
all of the safety issues associated with its use. It is the
responsibility of the users of this safety guideline to
establish appropriate safety and health practices and
determine the applicability of regulatory limitations
prior to use.
3 Limitations
3.1 This guideline does not include applicable fire and
safety code regulations.
3.2 The gases or liquids which should be monitored
are not listed.
3.3 This guideline does not suggest the appropriate
levels of detectability. Such levels may be determined
by reviewing accepted government and non-
governmental agency standards, such as those
promulgated by ACGIH, USEPA, and USOSHA.
3.4 Process related issues and corrective actions in the
case of gas leaks are not discussed in this guideline.
3.5 This guideline makes no recom mendation of any
specific technology or manufacturer, nor does it provide
installation and operation recommendations.
3.6 This guideline provides neither a comprehensive
list of all gases, nor recommended areas for monitoring
of toxic and flammable gases.
3.7 Not all known analytical methodologies for
monitoring of toxic and flammable gases are described
in this guideline.
4 Referenced Standards
4.1 SEMI Standard
SEMI E33 — Specification for Semiconductor
Manufacturing Facility Electromagnetic Compatibility
5 Terminology
5.1 Abbreviations and Acronyms
5.1.1 ACGIH — American Conference of Govern-
mental Industrial Hygienists
5.1.2 EMI — Electromagnetic interference
5.1.3 EU — European Union
5.1.4 RFI — Radio frequency interference
5.1.5 USEPA — United States Environmental
Protection Agency
5.1.6 USOSHA — United States Occupational Safety
and Health Administration
5.2 Definitions
5.2.1 challenge gas — a gas/chemical used to create a
response in the gas detection system.
5.2.2 conditioning — the necessity to expose a
gas/chemical sensor to the target gas/chemical to enable
more rapid detection of that gas/chemical.
5.2.3 fail-safe relay — an alarm relay that is “fail-
safe” returns to a safe operating condition when power
is lost.
5.2.4 filter lag — relative to gas/che mical sensors, the
time delay in the detection of a challenge gas/chemical
due to the incorporation of a chemical, mechanical or
electrical filter.