**Silicon Detector Facility**

**ODH Analysis**

Dan Olis 6/1/2004

LAB A Control Room Addendum

Herman Cease 4/8/05

LAB A Control Room LN2 Auto Fill System Addendum

Herman Cease 11/29/05

# 

# SUMMARY

A component of the Silicon Detector Facility's utility infrastructure is
a gaseous nitrogen header. Nitrogen is used primarily to purge
enclosures to eliminate ambient moisture and, in some cases, the
presence of oxygen. The Silicon Detector Facility (SiDet) includes Labs
A, B, C, D, A-B Bridge, C-D Cross-connect, and adjoining hallways. This
analysis is inclusive of all lab spaces within the facility that have
any part of the nitrogen header running through them or that are fed by
nitrogen piping drops. Separate calculations are included for each
portion of the facility that can be isolated by closed doors. This
analysis shows that all regions within SiDet are class 0 ODH
environments.

# 

Note: This document supercedes the ODH analysis done for the Lab A/B
Bridge. The analysis for that single volume has been revised and
incorporated into this facility-wide document.

**INTRODUCTION**

Gaseous nitrogen is primarily used in the Silicon Detector Facility for
purging enclosures of sensitive items. Although the plumbing system is
extensive, the total nominal flow rate into the facility less than 5
SCFM. Compared to facilities holding cryogenic piping, the nitrogen
supply at SiDet is very low risk. The supply is a 5000-gallon liquid
nitrogen dewar located outdoors at the north end of Lab D. It has an
operating pressure of 34 PSIG and relief valves set to 45 PSIG. A
gaseous nitrogen header is fed from the dewar through two Pennwalt CVI
vaporizers and the header pressure is nominally the same as the dewar's.
The header is piped throughout the facility, interconnecting piping in
Lab A, Lab B, Lab C, Lab D, Lab A-B Bridge, and the C-D Cross Connect
into a single system. Smaller lines drop from the header as take off
points where nitrogen is used. A restricting orifice outdoors in the
main feed puts an upper limit on the total possible flow into the
facility at 25 SCFM. Additionally, orifices in the individual branches
inside the facility limit downstream spills to 2-4 SCFM.

Spreadsheets are attached which show the ODH analysis for each isolated
space within the facility that is currently using nitrogen purge or that
has the header running through it. The analysis is done as described in
Fermilab ES&H chapter 5064, Oxygen Deficiency Hazards. This document
shows that all regions within SiDet are class 0 ODH environments.

# Si-DET PIPING AND PURGE USAGE OVERVIEW

The piping schematic of the header and dewar is drawing
9214.000-ME-435001. It is attached. The nitrogen header (indoors) is
plumbed entirely with type-K copper tube with sweated joints. At points
of delivery, flexible poly lines are most frequently used to make the
connection to purge enclosures. In addition to serving as a continual
purge supply, the nitrogen gas is used in some work areas to
periodically spray contaminants from delicate work pieces.

![](media/image1.wmf)It is facility policy that all purge enclosures use
a rotometer style flow meter to set and monitor usage. A summary of all
purge usage at the time of this writing of this document is shown in the
table below.

The left column shows how low the facility's nitrogen consumption is.
The right column of the table shows the assumed purge rates used in
these analyses. The table illustrates a fairly conservative overestimate
of the nitrogen consumption is used. This allows the facility to add to
or move a significant number of purge volumes around the system without
requiring a revision to this document.

A restricting orifice in the supply line connecting the dewar to the
facility limits the maximum flow of nitrogen into the facility to 25
SCFM. This orifice is outdoors. The calculation assumes a catastrophic
failure of the downstream piping and uses the dewar's relief valve
pressure, not the current operating pressure, as the differential
pressure across the orifice. Within the facility, the presence of flow
limiting orifices in each drop places a strict upper limit on the
nitrogen that can be delivered to a room (typically 2 SCFM). The piping
component totals, number of purge enclosures, and ventilation and spill
rates are presented for each separate enclosed room within the facility
in the following sections.

A time-delayed shutoff valve is installed in the gas supply just at the
inlet to the system. The valve is a normally closed solenoid, held open
by an uninterruptible power supply (UPS). The valve is EV-3101 on the
piping schematic. During short power outages, nitrogen flow to the
facility is maintained. During longer outages, the continued flow of
nitrogen into some clean rooms could present an oxygen deficiency hazard
since forced ventilation is lost. Purge rates are low, so the time to an
ODH risk is typically 24 hours or greater. A relay with a timer is set
to shutoff gas flow after a 12-hour loss of commercial power. This
system is wired for fail-safe operation. The bypass valve shown in the
schematic is to be opened only during maintenance and safety tests. It
is locked out and labeled with a yellow caution tag. The lock's key is
on file with the facility's secretary. This safety system is tested once
a year. A copy of the test log is included in the appendix. The tests
are the responsibility of the facility's systems technician.

This document assumes that each port on the gas line in an area has a
purge volume attached to it. The quantity of purge enclosures listed is
an upper limit estimate as to how many could be attached in a given
area. Since purges are 'intentional leaks' they are assigned a
probability of 1.0 in the calculations. The leak rate assigned to the
purge volumes is 0.1 SCFM (6 SCFH), a conservative estimate.

As stated previously, purge volumes are connected to the system through
a Dwyer style flow meter with integrated flow control valve. These flow
meters are counted as 'valves' in the analyses. In the spreadsheet
calculations, the total number of valves in an area includes all the
valves that are part of the hard copper piping plus additional flow
meter control 'valves' attached to ports in the piping to make use of
the nitrogen utility.

Some technicians make use of spray nozzles to periodically blow dust
from work pieces. This too represents an intentional 'leak' but the time
averaged usage is too small to consider. The spray nozzles are
commercial products and can also be accounted as 'valves' in the
analyses. There is not a separate line item in the calculations for the
spray nozzles since it is assumed that a spray nozzle would be used at a
port in place of a purge enclosure (with integrated flow control valve).
This is a conservative approach since these spray nozzles do not have a
continual purge rate associated with them.

# VENITILATION AND ODH ANALYSES FOR EACH LAB AREA

A description of the ventilation system and ODH analysis of each room
volume at\
SiDet is presented in the sections below. To simplify counting of joints
in the piping system, the number is estimated by conservatively assuming
one joint for every five feet of pipe length. A 5 SCFM spill rate is
assumed in leaky joints in the main header. Spill rates in leaky joints
in the branches of the system are smaller and assigned the maximum flow
rate allowed by the orifice controlling that branch. The leak rate for
catastrophic failure of a pipe or valve is assumed equal to the maximum
spill rate calculated for the controlling restricting orifice. For pipes
and valves in the main run of the header, 25 SCFM is used per the
discussion in the introduction. This calculation is in the appendix. In
side branches of the system, leak rates are assumed equal to the maximum
flow rate of the restricting orifice in that branch. These rates are
described in subsequent sections. The probability of failure of the
piping components is taken from the NEC tables included in FESHM 5064.
The probability of the 'leak rates' of the purge boxes is assigned to
1.0 since they are continually present.

Ventilation rates in the analyses for the building shells (*not* the
internal clean rooms) are generated by assuming each building's natural
leakiness, or infiltration, provides adequate fresh air for its
occupants and the operations taking place within it. The estimated
infiltration rate is a conservative estimate based on 1 building volume
change per day. The 1989 American Society of Heating and Refrigeration
Fundamentals Handbook shows this to be a conservative estimate. The
*Infiltration* section in Chapter 23 indicates that office buildings
constructed in mid-1980's have infiltration rates of 0.1 to 0.6 air
exchanges per hour. This is equivalent to 2.4 to 14.4 air exchanges per
day. The 1 volume change per day assumed in this analysis is
conservative for SiDet buildings.

Ventilation rates for clean rooms and smaller workspaces are measured
rates and described in more detail in the sections below.

Appended to the ODH Analysis spreadsheets are additional documents:
calculations, an explanation of the spreadsheet columns, sheets showing
the equations used in the spreadsheets, and a copy of the failure rate
tables taken from FESHM 5064.

#### Lab A

Lab A houses office space around the perimeter of the second floor and
technician workspace on the first floor. It also holds a large class
5000 clean room in the center of the building. Adjacent to the class
5000 clean room is a smaller class 1000 clean room. Nitrogen is used in
the first floor technician areas and in the clean rooms.

Six small HVAC units serve Lab A. Four of these units draw outside
makeup air (100 CFM each) but the units run only when heating and
cooling are called for. The estimated infiltration rate for the building
is 20 CFM and is simply a conservative estimate based on 1 building
volume change per day. The calculation is shown here:

$$\text{29000}\text{FT}^{3}x\frac{1\text{day}}{\text{24}\text{hrs}}x\frac{1\text{hr}}{\text{60}\text{min}\text{.}} = \text{20}\frac{\text{FT}^{3}}{\text{min}\text{.}}$$

There are many spaces within SiDet that have enclosures within larger
rooms (e.g. clean rooms within a larger building shell). In these cases,
the piping within these smaller rooms is included in the ODH analysis of
the larger room volume because a leak within the clean room may
eventually find its way into the larger volume. That is to say, the
smaller room is considered a part of the larger space it occupies. A
separate analysis is then done for the smaller interior spaces
(individual clean rooms) to prove that there is not a concentrated risk
as a result of the clean room enclosure.

The main nitrogen header in this space is 1" type-K copper. There is
currently one purge enclosure in the technician area drawing 0.01 SCFM
of nitrogen. The analysis assumes three may exist at some point in the
future, each drawing 0.1 SCFM. Furthermore it this analysis, it is
assumed that any nitrogen spill in the clean rooms finds its way into
the larger tech area. Therefore, the attached spreadsheet calculation
includes the piping components found in both the technician area and in
the clean rooms. Those components are summarized below and in the
spreadsheets in the appendix.

The calculation shows that Lab A is an ODH class 0 environment.

#### Lab A Class 5000 Clean Room 

The class 5000 clean room occupies the center of the building and the
volume extends up into the bubble-shaped roof. The space is more
accurately described as a semi-clean room because it is not sealed very
well to the inside of Lab A or to the outdoors through the roof. The
large presence of bugs and an occasional bird attest to its leakiness.

The room volume is filtered by large HEPA filters, fed by a McQuay Model
LYP108C 14-9/16" airfoil powered by a 10 HP motor. The measured makeup
rate is 100 CFM. It draws from the Lab A shell. Like all clean rooms, a
mechanical failure of the air-handling unit would be quickly recognized
and addressed.

The class 1000 clean room is a smaller volume contained inside the class
5000 clean room so the piping components in both areas are included
here. The attached analysis summarizes the current piping sizes and
lengths and the number of valves inside the clean rooms. The piping feed
to the clean room is a single ½" drop from the header. A restricting
orifice, located in the larger Lab A volume, limits the maximum flow of
nitrogen to 3.8 SCFM. The orifice calculation is included in the
appendix.

There are currently six enclosures in the class 5000 room and four in
the class 1000 room receiving nitrogen purge. The current consumptions
are 0.32 and 0.25 SCFM of nitrogen respectively. To be conservative, a
purge rate of 1.7 SCFM is used in the ODH analysis. This is calculated
by assuming a purge enclosure is added to each of the existing (10)
ports in the class 5000 room and the (7) ports in the class 1000 room.
It's assumed each draws 0.1 SCFM of nitrogen.

The analysis shows that the class 5000 clean room has an ODH class 0
rating. The first calculation shows the normal ventilation condition.
The second calculation includes the probability of failure of the
ventilation system. The probability assigned to the mechanical failure
of the air-handling unit was taken from Table 2 in FESHM 5064 for the
failure of an electrical motor (1x10^-5^events/hr). A column is added to
the table to multiply the probability of the leak times the probability
of a ventilation failure due to motor failure. The 5 SCFM fresh air
makeup rate used in this calculation is quite reasonable considering the
leakiness of the volume previously described.

Ventilation loss as a result of a power outage occurs more frequently at
Fermilab. Power outages typically last a few hours at most. Table 1 in
FESHM 5064 provides a 1-hour duration for unplanned outages. It would
take more than 98 hours of a 1.7 SCFM purge and zero makeup air to lower
the oxygen concentration in the clean room to 18%. This calculation is
included in the appendix. The 12-hour time-delay shutoff in the
facility's main nitrogen feed line eliminates any ODH concern for
long-term outages.

#### Lab A Class 1000 Clean Room

The class 1000 clean room sits between the class 5000 clean room and an
exterior wall. The ventilation system for the room is shown in the
following sketch. A Train Company ventilation unit cools the space but
draws no makeup air. The supply side of the unit discharges into the
drop ceiling, in a volume called a plenum. There are (18) fan-powered
HEPA units installed in the drop ceiling. Each unit includes a filter
and its own fan. These ceiling units draw air from the plenum space
within the drop ceiling and discharge into the room below. Each ceiling
unit moves approximately 616 CFM of air for a total delivery to the room
of 18 x 616 = 11,090 CFM of air. The plenum pressure is negative to the
room volume, running at approximately -0.08" WC. An intake attached to
the plenum draws makeup air from the larger class 5000 clean room. The
makeup rate is 100 CFM.

The attached analysis summarizes the current piping sizes and lengths
and the size and number of valves inside the clean room. The piping is
fed from the larger class 5000 clean room through a single ½" line. The
same size restricting orifice that controls flow to the class 5000 clean
room limits the maximum flow of nitrogen to 3.8 SCFM.

There are currently four enclosures receiving nitrogen purge. The
current consumption is 0.25 SCFM. To be conservative, a purge rate of
0.7 SCFM is used in the ODH analysis.

The analysis shows that the class 1000 clean room has an ODH class 0
rating. The first calculation shows the normal ventilation condition.
The second calculation includes the probability of a single point
failure of the ventilation system. The class 1000 clean room has a very
robust ventilation system since it is assembled from (18) parallel fans
on the HEPA units. With a failure of a single unit, seventeen are still
operational and the ventilation makeup is essentially unchanged.

It would take more than 36 hours of a 0.7 SCFM purge and zero makeup air
to lower the oxygen concentration in the clean room to 18%. This
calculation is included in the appendix. The 12-hour time-delay shutoff
in the facility's main nitrogen feed line eliminates any ODH concern for
long-term outages.

#### Lab A Control Room Addendum H. Cease 4/8/05

Attached to the Lab A area is an enclosed room known as the Lab A
Control Room. Utilities to the room include building nitrogen gas. A
restricting orifice (0.052" diam.) in the nitrogen gas line feeding the
room limits the maximum flow to 1.8 SCFM. The total room volume is
approximately 5500 FT^3^. The room is partitioned for a gowning area
reducing the room volume to approximately 3800 FT^3^. Infiltration to
the room is assumed to be one volume exchange per day --or about 2.6 cfm
makeup air. At no time does the nitrogen gas purge rate exceed the
natural infiltration rate of fresh air.

Three fan powered HEPA units in the ceiling circulate air throughout the
room. A baffle is used to take air from the LAB A general area and mix
it with the Control Room air at a rate greater than 20 FT^3^/min. The
Control Room has a positive pressure with respect to the surrounding Lab
A area. If a single fan fails, the mixing of air with Lab A remains
about the same. The fuse panel for the fans are locked out and labeled
with a yellow caution tag. The lock's key is on file with the facility's
secretary

LN2 will be used in the control room. The total room volume is
approximately 5500 FT^3^. The room is partitioned for a gowning area
reducing the room volume to approximately 3800 FT^3^. A 21 liter LN2
spill is allowed and maintains an ODH Class 0; the Oxygen partial
pressure does not dip below 18%. Using a fresh air makeup of 20
FT^3^/min, approximately 25 minutes are needed to return the partial
pressure of oxygen to 21.9%. Signs are posted to limit the amount of
liquid nitrogen in the room to 21 liters. A Job Hazard Analysis is
written to ensure workers understand proper personal protection when
handling liquid nitrogen, the limitation on the amount of liquid
nitrogen that can be stored in the control room, and no additional
liquid nitrogen to be brought into the room during a power failure.

#### Lab A Control Room with LN2 Auto Fill System Addendum H. Cease 11/29/05

An automatic LN2 fill system is replacing the need to hand fill small
dewars inside the Control Room. The automatic fill system has a 1000
liter dewar outside the building, a single plumbing line enters the
building and runs through the Lab A space, then into the Lab A control
room. The supply line of the 1000 liter dewar has a solenoid valve such
that in the event of a power failure, LN2 supply is stopped from
entering the building. The ODH in Lab A remains Class 0 since the
probability of a plumbing line failure is low independent of flow rate.
Oxygen monitors on the wall in the Lab A Control Room are used in a fail
safe mode where in the event of a power failure or a drop in the partial
pressure of Oxygen, the LN2 supply solenoid valve is closed. The Oxygen
monitor power is tied to the powered ventilation in the room. If power
fails to the ventilation, the Oxygen monitor power also fails, closing
the LN2 supply solenoid. The ODH in the Lab A Control Room is Class 0
since in the event of a failure, the LN2 supply is shut off.

The total room volume is approximately 5500 FT^3^. The room is
partitioned for a gowning area reducing the room volume to approximately
3800 FT^3^. A 21 liter LN2 spill is allowed and maintains an ODH Class
0; the Oxygen partial pressure does not dip below 18%. Using a fresh air
makeup of 20 FT^3^/min, approximately 25 minutes are needed to return
the partial pressure of oxygen to 21.9%. Signs are posted to limit the
amount of liquid nitrogen in the room to 21 liters. Although carrying in
hand flasks with LN2 is no longer needed, the amount of LN2 stored in
internal dewars remains limited to 21 liters.

A Job Hazard Analysis is revised to ensure workers understand proper
personal protection when handling liquid nitrogen, the limitation on the
amount of liquid nitrogen that can be stored in the control room, no
additional liquid nitrogen to be brought into the room during a power
failure, and to leave the room in the event the Oxygen monitor is
tripped.

#### Lab B Shop and Basement

Lab B houses a small machine shop and technician work area. It also held
the old Bubble Chamber and for that reason is the only building at SiDet
with a basement. The shop area and basement around the bubble chamber
are considered a single building volume since they are interconnected
through large openings.

Lab B has corrugated steel walls and a large rollup door to the outside.
The infiltration rate into the building due to the leaky nature of the
structure is estimated to be 35 CFM based on one building volume change
per day.

Lab B is the terminal branch of the nitrogen header. The pipe lengths,
number of valves, purge enclosures, and potential spill rates are
summarized in the appended analysis.

Freezers in the basement are purged with nitrogen to reduce the
accumulation of ice inside them. Currently, 0.03 SCFM of purge gas is
used. The analysis conservatively assumes 0.3 SCFM or purge may
eventually be drawn in the shop. A restricting orifice in the line
feeding this drop limits the maximum flow to 1.8 SCFM. The calculation
shows that the Lab B shop is an ODH class 0 environment.

#### Lab B Lotema Room

Three smaller rooms are attached to the larger Lab B shop. They are each
analyzed separately. The construction of these rooms is the same as the
rest of Lab B. The estimated infiltration rate into the Lotema Room due
to the leaky construction is 33 CFM.

The Lotema Room is usually used to setup tests and experiments. There
are currently no purge volumes in the room but nitrogen is sometimes
used as a purge when running cold tests to prevent the formation of
condensation on test pieces. A half-inch nitrogen header runs the
perimeter of the room. A restricting orifice in the line limits the
maximum flow into the room to 1.8 SCFM. For this analysis, it is assumed
that a second valve is attached to each of the five drops and each is
drawing 0.1 SCFM of nitrogen gas.

The attached analysis shows that the Lotema room is a class 0 ODH
environment.

#### Lab B Mycom and Norwalk Rooms

These rooms are fairly small (6300 ft^3^ for Mycom and 5000 ft^3^ for
Norwalk) so the estimated infiltrated rates do not provide enough
confidence that natural infiltration is an adequate source of fresh air.
Forced ventilation of 550 CFM is provided to each room with fans
(Comair-Rotron brand, Caravel model). The switches on the fans are
locked out and labeled with a yellow caution tag. The lock's key is on
file with the facility's secretary. The facility's systems technician
verifies operation regularly. A copy of the verification log is included
in the appendix.

The Mycom room is currently used as an assembly area. There are
currently two volumes in the room drawing 0.03 SCFM of nitrogen. A
half-inch nitrogen header runs the room's perimeter and includes three
drops. A restricting orifice in the line limits the maximum flow into
the room to 1.8 SCFM. For this analysis, it is assumed that a second
valve is attached to each of the three drops and each is drawing 0.1
SCFM of nitrogen gas.

The attached analysis shows that the Mycom room is a class 0 ODH
environment for both 'normal ventilation' and 'ventilation failure'
cases. A 1 CFM of infiltration was assumed for the ventilation failure
analysis. It is equivalent to a room air change every 4.3 days. A
calculation in the appendix shows that a leak of 0.3 SCFM of nitrogen
gas into the room will result in an oxygen level of 18% after 54 hours.
This calculation is included in the appendix. The 12-hour time-delay
shutoff in the facility's main nitrogen feed line eliminates any ODH
concern for outages of 12 hours or more.

The Norwalk room is currently used as an assembly area. Currently there
are no users attached to the nitrogen lines in the room. A restricting
orifice limits the maximum flow into the room to 1.8 SCFM. For this
analysis, it is assumed that a second valve is attached to each of the
three drops and each is drawing 0.1 SCFM of nitrogen gas.

The attached analysis shows that the Norwalk room is a class 0 ODH
environment for both 'normal ventilation' and 'ventilation failure'
cases. A 1 CFM of infiltration was assumed for the ventilation failure
analysis. It is equivalent to a room air change every 3.5 days. A
calculation in the appendix shows that a leak of 0.3 SCFM of nitrogen
gas into the room will result in an oxygen level of 18% after 43 hours.
This calculation is included in the appendix. The 12-hour time-delay
shutoff in the facility's main nitrogen feed line eliminates any ODH
concern for outages of 12 hours or more.

#### 

#### A-B Bridge

The A-B Bridge is a steel shell industrial building on a concrete pad.
It houses both offices and lab space. The building is ventilated by
AC-1, a Trane model YCH330 unit rated to deliver 11,000 CFM. The minimum
fresh air intake on the unit is 646 CFM but is delivered only when the
thermostat calls for operation. Like other industrial buildings, fresh
air is maintained by infiltration leakage. This number is estimated as
64 CFM.

The attached analysis summarizes the current piping sizes and lengths
and the size and number of valves inside the A-B Bridge. There are three
possible modes of nitrogen delivery to the bridge considered: full
rupture of the piping or valves, leakage from a joint failure on the
piping, and intentional purging of nitrogen gas into dry boxes. For
conservativeness, it is assumed that one purge box is used at each of
the eight nitrogen drops. There is currently only one enclosure in the
bridge that is fed a nitrogen purge. The total current purge consumption
is 0.01 SCFM of nitrogen. To be conservative, a purge rate of 0.8 SCFM
is used in the ODH analysis. This is calculated by assuming a purge
enclosure is added to each of the existing (8) drops from the nitrogen
header and each draws 0.1 SCFM. Since purging is intentional and
continual, the probability of this mode of delivery assigned in the
spreadsheet is 1.

The probabilities assigned to a pipe rupture, valve rupture, and leaky
joint (weld) are taken from Table 2 in FESHM chapter 5064. The spill
rate out of a leaking joint in the header is conservatively assigned 5
SCFM. The spill rate from a ruptured valve or pipe is 25 SCFM, the
maximum flow that can be delivered to the system. Orifices in each drop
limit the maximum flow rate to 0.9 SCFM. This calculation is in the
appendix.

The attached analysis shows that the Lab A-B Bridge is a class 0 ODH
environment.

#### Lab C

Lab C is an industrial building shell constructed on a concrete pad with
corrugated steel walls and an asphalt roof. The building is heated and
cooled by a unit that runs only when called for by a thermostat. The
building's natural leakiness, or infiltration, provides adequate fresh
air for its occupants and the operations taking place within it. The
estimated infiltration rate for the building is 69 CFM. The building
volume is 100,000 FT^3^.

The gaseous nitrogen supply header enters from the C-D Cross Connection
and exits towards Lab A. There is additional piping inside the Lab C
clean room, which resides in the volume of the Lab C shell. The nitrogen
is fed to the clean room through a single ½-inch line dropped through
the ceiling. Since the clean room is contained within the larger shell,
any nitrogen leak in the clean room eventually finds its way into the
larger high bay volume. The attached Lab C analysis summarizes the
piping found in the high bay and the clean rooms. The pipe lengths and
valve count are included. A spill rate of 25 SCFM for catastrophic
failure of components is used for piping in the high bay. The
flow-limiting orifice in the feed to SiDet sets this limit. The spill
rate from components inside the clean room is controlled by a
flow-limiting orifice in the ½-inch pipe feeding the clean room. The
maximum spill is 3.8 SCFM.

The calculation shows that the Lab C high bay is an ODH class 0
environment. Since the ventilation of the building is supplied by
natural infiltration, no analysis is required for the case of a
'ventilation failure'.

#### Lab C Clean Rooms

A glass wall separates the clean rooms into 'north' and 'south'. The two
sides are connected with a walk-through door and a large rollup door
(normally closed). The ventilation system is described in FESS drawing
number 8-2-125. The two sides have identical ventilation systems. Each
includes two parallel cooling units that feed a larger ventilation
blower with associated HEPA filtration. The cooling units each have a 5
HP direct-drive blower. They supply the suction side of an airfoil
scroll unit driven by a 10 HP motor. The makeup rate on each cooling
unit specified on the drawing is 500 CFM, or 1000 CFM of fresh air to
each clean room. Measurements indicate the makeup rate is currently 1240
CFM to the north and 1232 to the south. The analysis uses 1000 CFM per
the design specification. Ventilation makeup is drawn from the Lab C
shell.

The attached analysis summarizes the current piping sizes and lengths
and the size and number of valves inside the clean room. Since the
piping, ventilation, and sizes of the two halves are very similar a
single analysis is valid for both sides. The piping system is fed by a
single ½" drop from the header through the clean room roof. A
restricting orifice in the drop, located above the clean room roof,
limits the maximum nitrogen flow to 3.8 SCFM. The orifice calculation is
included in the appendix.

There is currently one enclosure in the north side and seven in the
south that are receiving nitrogen purge. The current consumptions are
0.14 and 0.25 SCFM of nitrogen respectively. To be conservative, a purge
rate of 1.0 SCFM per side is used in the ODH analysis. This is
calculated by assuming a purge enclosure is added to each of the
existing (10) ports on the nitrogen header and each draws 0.1 SCFM of
nitrogen. The valve total in the tables also shows that a valve is
assumed to be included on each purge enclosure.

The analysis shows that Lab C clean rooms have ODH class 0 rating. The
analysis in the appendix is for the normal ventilation condition. The
second condition to consider includes the probability of failure of the
ventilation system. This is discussed in the following paragraph.

From the perspective of controlling oxygen deficiency hazards, the
ventilation system is very robust. The system for each half of the clean
room includes three fans. Although a mechanical failure of the main HEPA
blower would reduce the nominal makeup, the smaller 5 HP units will very
easily draw the minimum makeup required to control the hazard. As stated
above, each half of the clean room normally is fed 1200 CFM of makeup
air. When considering the probability of mechanical failure of the
primary blower, it is calculated that only 2 CFM of makeup air is needed
to control the oxygen deficiency hazard. The parallel Liebert blowers
feeding the larger unit will continue to push 450 CFM of makeup air
through the system when the main unit is inoperable. This was determined
by a test. Therefore the hazard is controlled in the event of a
mechanical failure of the main blower. The probability of failure of two
of the three blowers is P~event~ = P^n^, where P = 1e-5 motor
failures/hr and n = 2 motors. Therefore the probability of a complete
loss of ventilation on either half of the clean room from mechanical
failure is 1e-10/hr and further calculation is not required.

Because each clean room has its own separate ventilation system, there
is an additional level of ventilation redundancy. Each clean room is
pressurized to 0.04"WC. A total failure of one unit, and subsequent
depressurization of the clean space, would cause leakage of air from the
other half of the clean room (whose ventilation system is still
operational) around the cracks in the window seals and around the
walk-through and rollup doors separating the two sides. A 1.4 in^2^ leak
area between the north and south clean rooms provides 5 CFM of air into
the depressurized room.

During a power outage, it would take more than 50 hours of a 1.0 SCFM
purge and zero makeup air to lower the oxygen concentration in the
either half of the clean room to 18%. This calculation is included in
the appendix. The 12-hour time-delay shutoff in the facility's main
nitrogen feed line eliminates any ODH concern for outages of 12 hours or
more.

#### C-D Cross Connect

The C-D Cross Connect holds both office and testing space. It is
constructed in the same style as other industrial buildings in the
complex. The building temperature is controlled by an HVAC unit that
runs only when the thermostat calls for heating or cooling. The
estimated infiltration rate for the building is 53 CFM, based on one air
exchange per day for the building's 75,600 FT^3^ volume.

The gaseous nitrogen supply header enters from Lab D and exits to Lab C.
Nitrogen gas is available in the testing area for purge volumes. The
attached analysis summarizes the piping found in the C-D cross connect.
The pipe lengths and valve count are included. A spill rate of 25 SCFM
for catastrophic failure of components is used for the overhead piping
while the flow-limiting orifice in the drops controls the maximum spill
in the testing area to 1.8 SCFM.

There are currently eight enclosures in the cross-connect receiving
nitrogen purge. The current consumption is 0.2 SCFM. To be conservative,
a purge rate of 1.1 SCFM is used in the ODH analysis. This is calculated
by assuming a purge enclosure is added to each of the existing (11)
ports on the nitrogen header and each draws 0.1 SCFM of nitrogen.

The calculation shows that the C-D cross connect is an ODH class 0
environment. Since the ventilation of the building is supplied by
natural infiltration, no analysis is required for the case of a
'ventilation failure'.

#### Lab D

Lab D is an industrial building shell constructed on a concrete pad with
corrugated steel walls and an asphalt roof. The building is heated and
cooled by AHU-1. The unit runs only when heating and cooling are
required. The building's natural infiltration provides adequate fresh
air for its occupants and the operations taking place within it. The
estimated infiltration rate for the building is 72 CFM, assuming one
volume change per day. The building volume is 103,800 FT^3^.

The gaseous nitrogen supply line enters the Silicon Facility through the
northeast corner of Lab D. Additionally, there is piping inside the Lab
D clean room and Bonding Area, which reside inside the shell of Lab D.
Since the clean room and bonding area are contained within the larger
shell, any nitrogen leaked in theses spaces will eventually find its way
into the larger high bay volume. The attached analysis summarizes the
piping found in the high bay, clean room, and bonding area. The pipe
lengths and valve count are included. A spill rate of 25 SCFM for
catastrophic failure of components is used for piping in the high bay.
The orifice outside the building that controls the total flow to the
facility sets this limit. The spill rate from components inside the
clean room and bonding area is controlled by flow limiting orifices in
the individual pipe drops to these spaces. This number is 1.8 SCFM.

The calculation shows that the Lab D high bay is an ODH class 0
environment. Since the ventilation of the building is supplied by
natural infiltration, no analysis is required for the case of a
'ventilation failure'.

#### Lab D Clean Room

The Lab D clean room resides inside the Lab D high bay. The clean room
has a separate air-handling unit (ACU-2) on the roof of Lab D. It draws
fresh air from outdoors. The makeup on the unit is 1100 CFM. The unit
runs continuously.

The attached analysis summarizes the current piping sizes and lengths
and the size and number of valves inside the clean room. The system is
fed by four ½" drops from the above header in the Lab D high bay. A
restricting orifice in each drop limits the maximum flow to 1.8 SCFM in
each line. The orifices are located in the drops above the clean room
roof. Therefore a catastrophic failure of any piping component results
in a maximum spill of 1.8 SCFM. The orifice calculation is included in
the appendix.

There are currently eleven enclosures in the clean room that are fed a
nitrogen purge. The total current consumption is 0.5 SCFM of nitrogen.
To be conservative, a purge rate of 2.4 SCFM is used in the ODH
analysis. This is calculated by assuming a purge enclosure is added to
each of the existing (24) ports on the nitrogen header and each draws
0.1 SCFM of nitrogen.

The attached analysis shows that with a ventilation rate of 1100 CFM
provided by the air-handling unit, the risk of death by asphyxiation
from the nitrogen system is very low and the space has an ODH class 0
rating.

In the event that forced ventilation to the clean room is lost due to a
mechanical failure of the air handling unit, the second table shows that
the simultaneous probability of a leak event and the mechanical
breakdown of the AHU is so unlikely that the clean room remains an ODH
class 0 environment. For this case, a minimum infiltration rate of 5 CFM
of fresh air is assumed due to leakage from the attached annex called
the Bonding Area. The Bonding Area has its own ventilation system and is
connected to the Lab D clean room by a walkthrough door and a large
rollup door. Both doors are usually closed but present enough of a leak
path around cracks to easily provide the 5 CFM used in the analysis.
Additional sources of leakage include stack effects to the outdoors
through the clean room's ventilation system as well as normal opening
and closing of doors.

The probability assigned to the mechanical failure of the air-handling
unit was taken from Table 2 in FESHM 5064 for the failure of an
electrical motor (1x10^-5^events/hr). A column is added to the table to
multiply the probability of the leak times the probability of a
ventilation failure due to motor failure.

Ventilation loss as a result of a power outage is a more frequent event
at Fermilab. Power outages typically last a few hours at most. Table 1
in FESHM 5064 provides a 1-hour duration for unplanned outages. It takes
30 hours of a 2.4 SCFM purge to lower the oxygen concentration in the
clean room to 18%. This calculation is included in the appendix. The
12-hour time-delay shutoff in the facility's main nitrogen feed line
eliminates any ODH concern for outages of 12 hours or more.

#### Lab D Bonding Area

The Bonding Area is adjacent to the clean room. It is a semi-clean space
heated and cooled by a small air-handling unit in the hallway. The AHU
delivers approximately 1400 CFM to the suction side of three HEPA units
installed in the ceiling. A makeup rate of 25 CFM is drawn from the high
bay.

The nitrogen header does not run through this area but some nitrogen is
fed to the room through plastic lines to feed dry boxes and as a utility
at some of the bonding stations. An orifice in the copper line that
feeds this space limits the maximum spill rate to 1.8 SCFM. The purge
volumes currently consume 0.2 SCFM but 1.0 SCFM is used in the analysis.
The analysis assumes one valve for each of the six bonding stations and
one on each of ten possible dry boxes.

From an ODH standpoint, the ventilation system is robust since it
includes the main blower on the AHU as well as individual fans on the
three ceiling-mounted HEPA units. Forced ventilation will still exist
with a single failure on the main blower or one of the HEPA units.
Furthermore, the adjacent Lab D clean room normally operates at 0.01"WC
of positive pressure. This provides a constant rate of leakage into the
bonding area through the large rollup door, walkthrough door, and pass
through window. A small 5 CFM of makeup air is assumed in the analysis
for the case of a mechanical breakdown of one of the HEPA units or the
main blower.

For both normal operation of the ventilation system and a possible
single mechanical failure in the system, the attached analyses show the
space has an ODH class 0. In the event of a power outage, it would take
23 hours of a 1.0 SCFM purge to lower the oxygen concentration in the
clean room to 18%. This calculation is included in the appendix. The
12-hour time-delay shutoff in the facility's main nitrogen feed line
eliminates any ODH concern for outages of 12 hours or more.

####