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6 Summary of Method 6.1 A test is performed by releasing tracer g as at a constant flow rate within an enclosure to simulate a worst case lea k and then measuri ng on the periphe ry of the enclosure for the presence or a…

SEMI F15-93 (Reapproved 1104)

TEST METHOD FOR ENCLOSURES USING SULFUR HEXAFLUORIDE

TRACER GAS AND GAS CHROMATOGRAPHY

This Test Method was technically reapproved by the Global Gases Committee and is the direct responsibility

of the North American Gases Committee. Current edition approved by the North American Regional

Standards Committee on July 11, 2004. Initially available on www.semi.org September 2004; to be

published November 2004. Originally published in 1993; last published June 1999.

1 Purpose

1.1 The purpose of this test method is to provide a

standardized method to test the ability of enclosures to

contain gases and vapors and a standardized format to

record and document test results.

2 Scope

2.1 This test method applies to any enclosure that

possesses a local exhaust (secondary ventilation)

system.

2.2 In this test method, the tracer gas of choice is sulfur

hexafluoride (SF

). It is recognized that other gases

have been used as tracers, but for the purposes of this

test method, tracer gas means SF

NOTICE: This standard does not purport to address

safety issues, if any, associated with its use. It is the

responsibility of the users of this standard to establish

appropriate safety and health practices and determine

the applicability of regulatory or other limitations prior

to use.

3 Limitations

3.1 This test method is intended to test the containment

ability of a local exhaust system within an enclosure

under the manufacturer’s specified operating

conditions. Thus, test data obtained by means of this

test method apply only to the local exhaust conditions

that existed within the enclosure during the testing.

Extrapolation of the test data to other exhaust operating

conditions is not usually possible.

3.2 Use of this test method requires knowledge of the

principles of gas analysis as well as flow and pressure

measurement, gas chromatographic instrumentation,

and gas sampling techniques.

3.3 An acceptable enclosure, as determined in Section

7.1, does not imply a safe condition for routine

equipment operation with a leak and/or a tubing/fitting

failure. An acceptable enclosure is one that will contain

potential worst case leaks in an emergency, non-routine

situation. The fact that an enclosure is acceptable does

not imply that the enclosure is safe to operate when a

hazardous gas leak has been detected.

4 Referenced Standards

4.1 SEMI Standard

SEMI S2  Environmental, Health, and Safety

Guidelines for Semiconductor Manufacturing

Equipment

4.2 ASTM Standards

ASTM E 260  Practice for Packed Column Gas

Chromatography

ASTM E 697  Practice for Use of Electron Capture

Detectors in Gas Chromatography

4.3 NFPA Standard

NFPA 704  Standard System for the Identification of

the Fire Hazards of Materials for Emergency Response

NOTICE: Unless otherwise indicated, all documents

cited shall be the latest published versions.

5 Terminology

5.1 Definitions

5.1.1 equivalent release concentration (ERC)  the

theoretical concentration of a process gas that would be

measured outside an enclosure in the event of a process

line failure. The ERC can be expressed as a percentage

of the TLV or PEL of the process gas.

5.1.2 hazardous production material (HPM)  for the

purposes of this test method, a gas or vapor that has a

degree-of-hazard rating in health, flammability, or

reactivity of 3 or 4, as ranked by NFPA 704, that is

used directly in a research, laboratory, or production

process that has as its end product materials which are

not hazardous.

1 American Society for Testing and Materials, 100 Barr Harbor

Drive, West Conshohoken, PA 19428-2959, Phone: (610) 832-9585,

Fax: (610) 832-9555, http://www.astm.org/

2 National Fire Protection Association, 1 Batterymarch Park, Quincy,

MA 02169, Phone: 1 617 770-3000, Fax: 1 617 770-0700,

http://www.nfpa.org/

SEMI F15-93 © SEMI 1993, 2004 1

6 Summary of Method

6.1 A test is performed by releasing tracer gas at a

constant flow rate within an enclosure to simulate a

worst case leak and then measuring on the periphery of

the enclosure for the presence or absence of tracer. The

lack of measurable tracer indicates that the release of

potentially hazardous gases or vapors within the

enclosure at the tracer injection point(s) will not result

in their migration to the outside of the enclosure. Gas

samples are taken by means of disposable syringes,

sample bags, or sample vials. Gas samples are

analyzed by means of electron capture gas

chromatography.

7 Procedure

7.1 Test Design

7.1.1 Determine the type of enclosure to be tested, such

as: non-access, access, vacuum pump, equipment

cabinet, or other.

7.1.2 Determine the volume of the enclosure.

7.1.3 Measure the exhaust flow rate from the

enclosure.

7.1.4 Calculate the air changes per minute of the

enclosure by dividing the exhaust flow rate (Section

7.1.3) by the enclosure volume (Section 7.1.2).

7.1.5 Calculate the time at which the tracer

concentration in the enclosure will achieve approximate

equilibrium. Concentration equilibrium occurs when

the tracer concentration in the enclosure stops changing

as a function of time for a constant tracer release rate.

Divide 3 by the air changes per minute to establish this

time. Use this as the time to take the first sample after

initiating a test. Appendix 1 provides a derivation of

the equilibrium time.

NOTE 1: This test method is intended to test the containment

ability of the local exhaust system within an enclosure when

operated according to the manufacturer’s specifications. Thus,

testing should be performed with the local exhaust operating

under its manufacturer's recommended conditions.

7.1.6 If an excess flow control system is used,

determine the trip point for each hazardous gas used. If

different gases are used in the enclosure, the largest trip

point should be used to calculate the tracer release flow

rate.

7.1.7 If no excess flow system or flow-restricting

orifice is used, the maximum accidental release rate

must be calculated from the known maximum system

pressure and either valve coefficients or tubing ID. An

equation for flow through straight tubing is provided in

Appendix 2.

7.1.8 In the absence of guidance in the above two

sections, a standard test is the release of tracer gas

through 6.35 mm (0.25 inch) OD by 0.89 mm (0.035

inch) wall tubing at a rate of 28 standard liters per

minute (slpm) (1 scfm). Appendix 3 derives a general

equation, A3-7, that can be used when this is not the

case.

7.2 Reagents and Materials  Use SF

diluted in an

inert gas, such as nitrogen or argon, as the tracer source,

to minimize measurement difficulties associated with

small leaks of pure SF

from the supply cylinder and its

associated piping.

7.3 Sampling

7.3.1 In selecting the location of samples collected

outside the enclosure, consider 1) potential leak points,

2) the direction of the release, and 3) laminar flow

characteristics in the area surrounding the enclosure.

Samples should be collected from all sides of the

enclosure, downstream in the prevailing room air flow,

and in the operating personnel occupancy areas.

7.3.2 The time required for the enclosure to reach

equilibrium should be considered when establishing the

time to begin sampling. The first sample after initiating

tracer flow should be taken at the enclosure equilibrium

time. Collect additional samples at 1 to 2 minute

intervals until the tracer source is shut off. One sample

should be taken 1 minute after the tracer source is shut

off. The test duration can be changed to accommodate

a particular test.

7.3.3 Collect background (baseline) samples from the

area surrounding the enclosure at predetermined

locations. When logistics permit, analyze the

background samples before releasing the tracer gas. If

background levels above approximately 1 ppb are

detected, evaluate the integrity of the SF

tracer

delivery system, and postpone the test until the

concentration is less than 1 ppb. Other sources of SF

in the immediate test area may also cause this

background.

NOTE 2: If testing is performed with an SF

background, the

background concentration must be measured and subtracted

from any subsequently measured tracer concentration value.

7.3.4 Release tracer gas within the enclosure being

tested by means of an injection manifold, shown

schematically in Figure 1. The tracer injection

manifold must be capable of measuring flow rates to an

accuracy of ± 5%. The tracer gas delivery line must be

routed into the enclosure and attached to a potential

leak point without violating the integrity of the

enclosure.

NOTE 3: To minimize tracer gas contamination of the area

surrounding an enclosure during a test, the end of the tracer

SEMI F15-93 © SEMI 1993, 2004 2

injection line should be capped, except when performing an

injection test.

7.3.5 Perform several tests with differing directions of

release relative to any opening or penetration in the

enclosure. The location and direction of the release

shall effectively simulate an actual gas release or

tubing/fitting failure within the enclosure. A worst case

failure can be simulated by locating the tracer injection

point at the potential leak location closest to a

penetration or opening within the enclosure with the

direction of tracer injection pointed directly at the

opening or penetration.

7.3.6 After initiation of tracer injection, collect grab air

samples from the area surrounding the enclosure at

predetermined times and locations. These samples

should be analyzed immediately after collection. If this

is not possible, they should be sealed. Label the

samples as to time and location. Samples may be taken

with: a) Containers that are non-absorbent, inert, and

that have low permeability (such as polyvinyl fluoride

film or polyester film sample bags or polyethylene,

polypropylene, nylon, or glass bottles) or b) disposable

syringes. Disposable syringes can be used to inject

samples into the gas chromatograph directly.

7.3.7 Record: a) the actual (measured) tracer gas

release rate, b) the actual SF

concentration in the tracer

gas being used, and c) the actual release time during a

test.

7.3.8 Collect air samples as described in Section 7.3.6,

and analyze them for the presence or absence of tracer

gas using a gas chromatograph. The measurement of a

non-zero tracer concentration in the area surrounding an

enclosure indicates incomplete containment of

contaminants within the enclosure.

7.3.9 Analyze samples according to ASTM E 260 and

ASTM E 697 in conjunction with the chromatograph

manufacturer's operating procedures. Samples may be

analyzed immediately after a test, or they may be stored

for future analysis. Experience has shown no

degradation of concentration in polypropylene syringes

when stored for several months as long as the needle or

syringe is plugged. Polypropylene syringes should be

discarded after one use to eliminate the possibility of

cross contamination of samples.

8 Calculations and Interpretation of Results

8.1 The maximum concentration of SF

measured in a

sample collected outside the enclosure is used to

calculate the Equivalent Release Concentration (ERC)

by the following formula:

ERC =

Conc. o

process gas



Measure

Conc.

Tracer Injection gas conc.

8.1.1 The above formula assumes the process gas

tubing that fails is the same diameter as the tracer gas

injection tubing. Appendix 3 contains a general

equation that can be used when this is not the case.

8.2 Compare the Equivalent Release Concentration to

the hazardous process gas TLV or PEL, whichever is

lower. If the ERC is above the prescribed limits, the

enclosure is not considered to be acceptable; if the ERC

is less than or equal to the prescribed limit, the

enclosure is considered acceptable. SEMI S2

recommends appropriate control limits for an enclosure.

9 Reporting Results

9.1 Present all results in tabular form in a manner

which unambiguously notes those enclosure(s) that do

not satisfy the criteria of SEMI S2. The exhaust

operating conditions during each test must be provided

along with each measured ERC value.

9.2 Describe tracer gas injection points within

individual enclosures to detail location and proximity to

openings, penetrations, exhaust grillwork, access

panels, and other potential leakage sites, such that worst

case leak conditions have been simulated.

9.3 Describe the unit being tested by manufacturer,

model number, and serial number to provide

identification of the unit being tested.

9.4 Tabulate and record the name, supply

concentration, maximum flow rate, and TLV or PEL for

each hazardous gas or vapor used within each enclosure

being tested.

Figure 2

Schematic Drawing of Injection Manifold