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SEMI S18-1102 © SEMI 2002 22 R2-2.5 Provide explosion ventin g for gas cabinet s and enclosu res to limi t overpressure inside gas cabinets a n d enclosures to 0.25 psig (1.7 kPag). Explosion venting can be provided by d…
SEMI S18-1102 © SEMI 2002 21
Table R2-1 Silane Flow Rates Through Restricted Flow Orifices Based on the Predictionsfrom the Factory
Mutual Research Model
Silane Flow Rate [scfm]
(Source Temperature: 77°F; Downstream Pressure: 0 psig; Discharge Coefficient: 0.8)
RFO Dia.
in. (mm)
Source Pressure [psig]
1500 1200 1000 800 600 400 200 100 50
0.020
(0.51)
10.0 7.88 6.04 4.34 3.02 1.92 0.949 0.497 0.288
0.014
(0.36)
4.91 3.86 2.96 2.13 1.48 0.941 0.465 0.243 0.136
0.010
(0.25)
2.50 1.97 1.51 1.08 0.755 0.480 0.237 0.124 0.069
© 2001 Factory Mutual Insurance Company. Reprinted with permission from FM Global Property Loss Prevention Data Sheet 7-7
‘Semiconductor Fabrication Facilities’
R2-2 Explosion Potentials
R2-2.1 Silane Ventilated Enclosure Example
R2-2.1.1 Consider the case of a ventilated enclosure of 25.9 ft (0.73 m) volume, swept by a ventilation flow of 450
scfm (12,744 lpm). Silane is supplied to the enclosure by a 1/4-in. (6.3 mm) (OD) line at a regulated pressure of 50
psig (3.4 bar). This line is in turn fed from a source at 1450 psig (100 bar), through a 10-mil restricted flow orifice
(RFO), located at a distance of 80 ft (24.4 m) from the ventilated enclosure. Safe operation of the system is
determined by the evaluation of two conditions:
• the magnitude of the initial silane inventory in the 1/4-in. (6.3 mm) line relative to the size of the enclosure, and
• the magnitude of the RFO-controlled flow relative to the ventilation in the enclosure. The first condition
determines the severity of a potential ignition transient at flow start-up. The second provides a measure of the
pressure development at flow shut-off.
R2-2.2 The standard silane inventory in the line is calculated by first determining the volume of the line [assume
0.035 in. (0.9 mm) wall thickness]:
V
line
= π / 4 (0.25-2×0.035)
2
× 80 × 12 = 24.43 in
3
The silane volume, when expanded to standard conditions, is given by (cf. Eq. 1):
∆Vstd = 24.43 × 0.0708 × 50 (1 + 8.19 10
–7
×
50
2
) = 86.66 in
3
= 0.05 ft
3
The ratio of the volume of the enclosure to the standard volume of silane is:
Vencl / ∆Vstd = 25.9 / 0.05 = 518
R2-2.3 Since this value is greater than 100, the situation is acceptable from the point of view of potential pressure
transients caused by ignition of the release at flow startup.
R2-2.4 Verifying the second condition requires calculating the RFO-controlled flow. By interpolation of the data in
Table 2, the flow through a 10-mil orifice from a source at 1450 psig (100 bar) is estimated to be equal to 2.41 scfm
(68.25 lpm). Since the maximum silane flow rate that can be accepted for a ventilation of 450 scfm (12,744 lpm) is
1.8 scfm (51 lpm) (450/250, see recommendation 3 above), this situation is not acceptable. It would become
acceptable if the ventilation flow was increased to 600 scfm (16,992 lpm) (2.41 ´ 250) or if the explosion venting
conditions shown in Figures R2-2a and R2-2b were to be satisfied.
SEMI S18-1102 © SEMI 2002 22
R2-2.5 Provide explosion venting for gas cabinets and enclosures to limit overpressure inside gas cabinets and
enclosures to 0.25 psig (1.7 kPag). Explosion venting can be provided by door panels, windows, louvers or exhaust
duct openings. Size explosion venting to satisfy both the requirements for line inventory pressure (Figure R2-2a) and
for the volume of the enclosure (or cabinet) (Figure R2-2b).
© 2001 Factory Mutual Insurance Company. Reprinted with permission from FM Global Property Loss Prevention Data Sheet 7-7
‘Semiconductor Fabrication Facilities’
Figure R2-2a
Vent Area Requirement for Prompt Ignition of Silane Releases as a Function of Initial Line Pressure
© 2001 Factory Mutual Insurance Company. Reprinted with permission from FM Global Property Loss Prevention Data Sheet 7-7
‘Semiconductor Fabrication Facilities’
Figure R2-2b
Vent Area Requirements for Ignition of Silane Releases at Shut-Off as a Function of Enclosure Volume
SEMI S18-1102 © SEMI 2002 23
RELATED INFORMATION 3
EXAMPLES OF SIMPLIFIED VALVE AND PIPING DIAGRAM FOR GAS
SUPPLY
NOTICE: This Related Information is not an official balloted part of SEMI S18. It is included to assist the user of
the document in understanding effective control systems. Publication is authorized by vote of the responsible
committee.
P
r
o
c
e
s
s
G
a
s
C
y
l
i
n
d
e
r
Vacuum
Generator
Supply
Vacuum
Generator
Valve
Vacuum
Generator
To Vent
Low Pressure
Vent Valve
To Process
Low Pressure
Gas Valve
2 Stage
Regulator
High Pressure
Gas Valve
P
r
o
c
e
s
s
G
a
s
C
y
l
i
n
d
e
r
Purge
Gas
Purge Gas
Valve
Automatic
Cylinder Valve
High Pressure
Vent Valve
Figure R3-1
Gas Supply System
NOTICE: 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.
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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
f
the contents in whole or in part is forbidden without express written
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