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SEMI S14-0704 © SEMI 2000, 2004 18 R4-4.2 In relation to th e occurrence of hazardous explosive atmo spheres, the origin of the po tentially explosive atmos phere should be described. This shoul d include: R4-4.2.1 The s…

SEMI S14-0704 © SEMI 2000, 2004 17

RELATED INFORMATION 4

DOCUMENTING EXPLOSION SAFETY FOR SEMICONDUCTOR

MANUFACTURING EQUIPMENT

NOTICE: This related information is not an official part of SEMI S14 and was derived from the work of a member

of the Fire Protection Task Force of the North American Environmental, Health, and Safety Committee. This

related information was approved for publication by 2/3 committee vote on July 17, 2003.

R4-1 Introduction

R4-1.1 The design of many semiconductor

manufacturing machines has to take account of the

hazard created by the presence of flammable liquids

and gases and as a result the designer will usually have

identified the hazards and put in place the necessary

mitigation and protection measures to provide a

satisfactory level of safety.

R4-1.2 This document is intended to assist equipment

designers and third party evaluators in documenting the

presence of explosion hazards and detailing how they

have integrated explosion safety into the design.

R4-1.3 There are specific requirements with regard to

the prevention and mitigation of explosion risks within

many jurisdictions. However the theory of explosion

prevention and mitigation transcends jurisdictional

boundaries. While this document arises out of the need

for some equipment to satisfy the European Union

ATEX Directive (94/9/EC), it has been developed in

such as way that it will not only meet the requirement

to document the principles of integrated explosion

safety (Essential Health and Safety Requirement 1.0),

but will provide information to authorities having

jurisdiction (AHJs) in many other parts of the world.

R4-2 Documentation

R4-2.1 For all equipment using flammable liquids or

gases an Explosion Risk Document (ERD) should be

developed and issued as an appendix to the SEMI S14

Fire Risk Assessment Internal Report. (The main

explosion hazards, risks and mitigation features should

already be documented in the S14 Final and Summary

Reports.)

R4-2.2 The ERD should demonstrate that the

equipment designer and manufacturer have adopted an

integrated approach to explosion safety adequately

mitigating the risk of an explosion.

R4-2.3 The structure of the document is flexible,

however a logical structure should be adopted such as

that suggested by the headings and sections of this

document, e.g.,

• Design Philosophy and Equipment Operation

Overview,

• Hazard Identification,

• Mitigation Measures Implemented & Protection

Systems Integrated, and

• Residual Explosion Risk.

R4-3 Design Philosophy and Equipment

Operation Overview

R4-3.1 The intended purpose of the equipment should

be stated, along with its operating environment.

R4-3.2 A functional and technical overview of the

process should be provided, where it relates to the

flammable and explosive chemicals and gases. This

should include significant process parameters including

temperature, pressure, and quantities of relevant

chemicals and gases. The operating conditions and

control system faults that influence explosion safety

should be described.

R4-3.3 The explosion protection design philosophy

should be thoroughly documented listing the design

standards applied, and any significant deviations.

R4-3.4 The classification of hazardous areas or zoning

outside and inside equipment should be described

indicating the classification system used (e.g., EN1127-

1, NFPA 497).

R4-3.5 Where components and equipment are within

or are related to areas classified as hazardous, they

should be documented including manufacturers’ details,

listings and approvals and confirmation that they have

been used within the scope of the approvals and

listings.

R4-4 Hazard Identification

R4-4.1 It is good practice to adopt a comprehensive

approach to hazard identification when designing for

explosive atmospheres, especially for complicated

equipment, protective systems and components. If a

structured approach to hazard identification and risk

assessment has been taken, for example, if during the

design process a HAZOP has been undertaken, the

HAZOP itself should form part of the documentation

supporting this section.

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

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.

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