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SEMI S5-0703 © SEMI 1993, 2003 1 SEMI S5-0703 SAFETY GUIDELINE FOR SIZING A ND IDENTIFYING FLOW LIMITING DEVICES FOR GAS CYLINDER VALVES This safety guideline was technical ly approved by the Global Gases Committee and i…

SEMI S4-0304 © SEMI 1992, 2004 7

RELATED INFORMATION 2

REGIONAL INFORMATION

NOTICE: This related information is not an official part of SEMI S4 and was derived from task force members'

knowledge and various references. This related information was approved for publication by letter ballot on

December 4, 2003.

R2-1 Purpose of this Related Information

R2-1.1 This Related Information was intended, at the

time of original publication, by the EHS Committee to

provide additional information and references on the

separation of chemicals, as practiced or regulated in

specific geographical regions.

R2-1.2 It is envisioned that the EHS Committee in

each Region of the SEMI Standards Program will

provide the appropriate text for its geographical region.

R2-2 North America

R2-2.1 Requirements for the separation of chemicals

can be found, for example, in both the International

Building Code (IBC) and the International Fire Code

(IFC). These requirements deal with the segregation of

incompatible chemicals in separate cabinets and

separation by barriers/distance in storage rooms. These

requirements can be found in the 2000 IBC section

415.9.5.9 and Table 415.9.5.9 and in the 2000 IFC

sections 2703.8.5 and 2703.9.8.

R2-3 Japan

R2-3.1 In Japan, requirements for the separation of

incompatible gases can be found in the High Pressure

Gas Safety law and related notifications from Ministry

of Economy and Industry, such as in section 11 of

“Notification regarding technical standards for

Location, Construction, and Facility of Manufacturing

Plant”.

NOTICE: SEMI makes no warranties or

representations as to the suitability of the safety

guidelines set forth herein for any particular

application. The determination of the suitability of the

safety guidelines 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 or

equipment mentioned herein. These safety guidelines

are subject to change without notice.

By publication of this safety guideline, Semiconductor

Equipment and Materials International (SEMI) takes no

position respecting the validity of any patent rights or

copyrights asserted in connection with any item

mentioned in this safety 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.

International), 3081 Zanker Road, San Jose, CA 95134. Reproduction o

the contents in whole or in part is forbidden without express written

consent of SEMI.

SEMI S5-0703 © SEMI 1993, 2003 1

SEMI S5-0703

SAFETY GUIDELINE FOR SIZING AND IDENTIFYING FLOW LIMITING

DEVICES FOR GAS CYLINDER VALVES

This safety guideline was technically approved 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 April 11, 2003. Initially available at www.semi.org June 2003; to be

published July 2003. Originally published in 1993.

NOTICE: This document was completely rewritten in

2003.

1 Purpose

1.1 The purpose of this safety guideline is to provide a

method to size and identify flow limiting devices that

limit the rate of release of hazardous gases from the gas

cylinder valve during transportation, storage, and use.

2 Scope

2.1 This safety guideline provides a method to identify

flow limiting devices by size, and to calculate

maximum and minimum flow rates so that the size

required can be determined. Specific SAFETY

WARNINGS are contained in Section 3.

2.2 This safety guideline pertains to flow limiting

devices for valves on cylinders containing hazardous

gases. These devices are intended to limit the flow rate

of uncontrolled releases of gases at or downstream of

the valve outlet. This guideline does not pertain to gas

releases caused by failure of the cylinder, the valve

connection to the cylinder, actuation of the cylinder

pressure relief device, or some failures of the valve.

2.3 This safety guideline pertains to flow limiting

devices operating at critical flow rates that result from

cylinder pressures greater than 103 kPa (15 psig).

Generally,

flow limiting devices are not used for

cylinders pressurized less than 103 kPa (15psig)

because the size required to provide adequate flow for

the process is so large that flow reduction resulting

from the flow limiting device would be minimal.

NOTICE: This safety guideline does not purport to

address all of the safety issues associated with its use.

It is the responsibility of the user of this guideline to

establish appropriate safety and health practices, and

determine the applicability of regulatory limitations

prior to use.

3 SAFETY WARNINGS

3.1 Installation  Only the gas supplier or cylinder

owner should install, remove, or otherwise service the

flow limiting device. Special equipment and

procedures may be required to perform any installation

or service operation safely. No other person should

install, remove, replace, clean, adjust, or otherwise alter

the flow limiting device unless authorized by the

cylinder owner.

3.2 Verification — When a flow limiting device is

required, the user should always verify that the size is

identified by tag, label or marking on the cylinder or

cylinder valve exterior, and that the device size

indicated matches the requirement. If a required flow

limiting device is missing, the cylinder should be

rejected prior to use.

3.3 Purging  The addition of a flow limiting device

in the cylinder valve may restrict gas flow during

purging. The user should assure that adequate purging

methods are used to prevent plugging the flow limiting

device. As a minimum, the operator should purge the

valve outlet after use with the same procedure used for

purging the valve outlet just after installation of the

cylinder. This is important to prevent contamination in

the valve outlet and reduce the probability of creating a

hazard at the cylinder supplier’s plant.

3.4 Blockage  Under certain conditions, some

hydrides such as diborane can polymerize and cause

obstruction or total blockage of flow limiting devices.

Care should be taken with cylinders that seem to be

empty, but may contain product.

4 Referenced Standards

4.1 SEMI Standard

SEMI S2 — Environmental, Health, and Safety

Guideline for Semiconductor Manufacturing Equipment

4.2 NFPA Document

NFPA 704  Standard System for the Identification of

Fire Hazards of Materials

NOTICE: As listed or revised, all documents cited

shall be the latest publications of adopted standards.

Regional standards may be substituted provided they

are equivalent. Equivalent international standards if

adopted, will be referenced in the next revision of this

guideline.

1 National Fire Protection Association, Batterymarch Park, Quincy,

MA 02269 Website: www.nfpa.org

SEMI S5-0703 © SEMI 1993, 2003 2

5 Terminology

5.1 Definitions

5.1.1 equivalent orifice — a passage that will allow

fluid flow equivalent to a round hole at 80% efficiency.

The efficiency, known as the orifice coefficient, will

typically vary from 65% (.65) for a sharp entrance to

95% (.95) for a well-rounded entrance. A flow rate

tolerance of ± 20% is used in Table 1 to allow for

variations in the entrance geometry and passage size.

Figure 1 illustrates the flow rate variation resulting

from this tolerance for different equivalent orifice sizes.

5.1.2 flow limiting device  a device installed in a gas

cylinder valve that will reduce maximum flow from the

valve under full flow conditions.

5.1.3 flow rate  flow rates in this guideline are given

in standard liters per minute (slm) at the standard

conditions of 0°C (32°F) and 101 kPa absolute (14.7

psia). This corresponds to the standard conditions used

for calibration of mass flow controllers used in

semiconductor processing systems.

5.1.4 hazardous gases  gases that have a degree of

hazard rating in health, flammability, or reactivity of

class 3 or 4 in accordance with NFPA 704, or

equivalent rating by a regional standard.

5.1.5 mixing gas — an inert gas used to dilute another

gas.

6 Flow Limiting Device Criteria

6.1 Where Used  Flow limiting devices should be

installed or incorporated into cylinder valves that are

used for gas cylinders containing the hazardous gases

listed in Table 2. Table 2 lists hazardous gases for

which devices are known to be feasible by reason of

testing and experience. SEMI encourages testing by its

members of hazardous gases not listed in Table 2 so

that new information can be added.

6.2 Materials  The flow limiting device should be

made of materials that are compatible with the gas in

the cylinder.

6.3 Installation  The flow limiting device should be

installed by the gas supplier or cylinder owner. See

Safety Warnings.

6.4 Identification  The preferred method of

identifying flow limiting devices is by equivalent

orifice size as shown in Table 1. Other means of

identification, requiring identification by the supplier as

to the device installed, may be used if unambiguous.

6.5 Service Life  Removable flow limiting devices

may be reused, but should be tested by the gas supplier

or cylinder owner before each use to assure that the

flow rate is as listed in Table 1.

6.6 Sizing  A flow limiting device that will not allow

nitrogen flows out of the valve outlet to exceed the flow

rates listed for its equivalent orifice size in Table 1.

The flow limiting device should be the smallest size

that satisfies the process requirements. The user should

make the choice of flow rate based on safety

philosophy contained in SEMI S2.

NOTE 1: Flow rates determined by the calculations in this

safety guideline are based on critical flow where the cylinder

pressure is equal or greater than 2 atmospheres and pressure at

the outlet of the flow limiting device is 1 atmosphere.

Consult the flow limiting device supplier to determine the

minimum size that will provide the required process flow rate

when cylinder absolute pressure is less than 2 times outlet

absolute pressure.

7 Flow Rate Calculations

7.1 The flow rates in Table 1 are specified for critical

flow of nitrogen through the flow limiting device at

several cylinder pressure levels. Densities are given in

Table 2 for some hazardous gases. First determine the

critical flow of nitrogen through the flow limiting

device from Table 1, or calculate using the method

specified in Section 7.2. Then, using the method

specified in Section 7.3, calculate the gas and pressure-

corrected flow rates to determine the proper flow

limiting device size for the application. For gas

mixtures, the density can be calculated using the

method specified in Section 7.4.

7.2 Nitrogen Flow Rate— Nitrogen flow rate

correction for cylinder pressures not listed in Table 1

follows:

NOTE 2: This equation is only valid for ideal gases, and

critical flow that results for most gases when P

cyl

atm

≥ 2.

It is necessary to multiply the equation by a compressibility

factor (Z) for better accuracy, however for nitrogen at

temperatures between -54 to +60°C (-65 to +140°F) and at

cylinder pressures less than 21,000 kPa gauge (3045 psig), the

result will be accurate within a few percent.

= Q

atmNT

atmcyl

Equation 1.

is the critical flow rate in slm of nitrogen at

pressures not listed in Table 1.

is the critical flow rate in slm of nitrogen from

Table 1 that corresponds to a given equivalent orifice

size at pressure.

cyl is the gauge pressure kPa gauge (psig) in the gas

cylinder for which the flow rate is being calculated.