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injection line should be capped, excep t when performing an injection test. 7.3.5 Perform several tests with differing d irections of release relative to any opening or penetration in the enclosure. The location an d dir…

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

10 Related Documents

29 CFR 1910.1000  Code of Federal Regulations,

Title 29, Superintendent of Documents, U.S.

Government Printing Office, Washington, D.C. 20402.

ACGIH  American Conference of Governmental

Industrial Hygienists, 6500 Glenway, Building D-7,

Cincinnati, OH 45211-4438, (513)661-7881. Industrial

Ventilation - A Manual for Recommended Practice,

20th ed. ISBN: 0-936712-65-1.

American Industrial Hygiene Association  345 White

Pond Drive, Akron, OH 44320, (216)873-2442.

Workplace Environmental Exposure Level Guides.

ASTM  American Society for Testing and Materials,

1916 Race Street, Philadelphia, PA 19103. ASTM

Standard E741-83 (Determining Air Leakage Rate by

Tracer Dilution).

BOCA  Building Officials and Code Administrators

International Inc., 4051 West Flossmoor Road, Country

Club Hills, IL 60478-5795, (708)799-2300. National

Fire Prevention Code.

Grot, R.A. and P.L. Lagus  “Applications of Tracer

Gas Analysis to Industrial Hygiene Investigations,”

Industrial Hygiene News, May 1991.

Orcutt, J.R.  “Characterization of Hazardous Gas

Releases by Tracer Gas Simulation,” Hazardous

Assessment and Control Technology in Semiconductor

Manufacturing, ACGIH, Cincinnati, OH, 1988.

SBCCI  Southern Building Code Congress

International, 900 Montclair Road, Birmingham, AL

35213-1206, (205)591-1853. Standard Fire Prevention

Code.

Tubby, R.L.  “Tracer Gas Testing of Secondary

Exhaust Systems on Hazardous Gas Enclosures,” SSA

Journal, Vol. 5, June 1991.

UFC  Uniform Fire Code. International Conference

of Building Officials and Western Fire Chiefs

Association, 5360 South Workman Mill Road, Whittier,

CA 90601. 1988 Edition, ISSN 0896-9736.