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Matt:<br>
<br>
I think that this is a very good point of discussion and expect that
a number of folks will weigh in. I certainly expect to learn some
things from many of my esteemed colleagues, but will also share with
you what I believe to be an appropriate prioritization. Of course,
my disclaimer is that I am not a registered PE and certainly would
not claim to be an authority on fire and other relevant code ...
plus, what I do know about code is based almost exclusively on
California Fire Code and may not be applicable in other states or
countries.<br>
<br>
I certainly believe that there are likely to be locale-to-locale
code variations that have an impact plus probably an even greater
variation in how your AHJ (Authority Having Jurisdiction) interprets
a given set of code. Plus, most of the relevant code of which I am
aware tells you WHEN you need to have gas detection but often
doesn't tell you either where those detectors need to be located or
how many of them you need. Of course, this discussion is all
heavily influenced by the level of toxicity of the gas we are
describing. My assumption is that we are discussing either toxic or
highly toxic materials where California code, at least, requires gas
detection. Finally, at the end of the day, regardless of what code
requires, I believe that we all want/need to be comfortable that we
have an appropriate collection of detectors that are able to detect
leaks in an appropriate fashion so as to protect the people in and
around our laboratories.<br>
<br>
Even though we have a facility that is about 30 years old, we
completely replaced our aging gas monitoring system in January, 2012
so that is the relevant date to think of in terms of when we (and
the officials at Santa Clara County Fire) last considered these
issues.<br>
<br>
I believe that California code requires us to have gas detectors for
any toxic or highly toxic gas in the gas cabinet and in any location
where there are non-welded connections. That typically means that
we have to have a detector in the gas box/vented enclosure of the
tool and in the VMB if there is one. California code, at least,
only requires that those be set at 1/2 IDLH alarm points. We,
however, choose to set all of our detectors ... even in enclosed
spaces ... to alarm at PEL, rather than 1/2 IDLH levels. There are
a few reasons for this:<br>
<br>
1. Small leaks tend to become big leaks over time. I'd personally
rather deal with a small leak today than a bigger leak tomorrow.<br>
<br>
2. In gas cabinets in particular, where exhaust flow is very high,
even a good sized leak will be diluted by that air flow and may not
reach 1/2 IDLH.<br>
<br>
3. Since exhausted spaces will be at negative pressure relative to
their surroundings, the presence of gas outside the enclosure (which
is generally an occupied breathing space) will be drawn into the
enclosure and be detected there. If detectors are set to alarm at
PEL levels, you can often successfully argue that a detector
monitoring the exhausted tool enclosure is also doing "double duty"
and detecting that same gas close to, but outside of, the exhausted
enclosure.<br>
<br>
However, we do not rely entirely on detectors in exhausted
cabinets. In the clean room, we do have a reasonable number of
breathing air detectors.<br>
<br>
In general, we do not have detectors at the exhaust of pumps after
the tools. For the most part, we know that there will be nasty
stuff in there. We rely on our breathing air detectors to tell us
when something (such as a flex line ...) in the pump exhaust system
has failed.<br>
<br>
We do have one detector in the exhaust of an abatement system that
is actually monitoring ammonia abatement in a GaN system. Why
monitor the ammonia abatement when we don't monitor the other
abatement systems that often have more toxic gases? Vendor-specific
requirement ...<br>
<br>
To answer your question of prioritization I would include an
appropriate number of sensors in the exhaust of gas cabinets, the
exhaust of tools (and in a VMB, if any) plus the appropriate number
of sensors in breathing air all in the High Priority category.<br>
<br>
I would include detectors in exhaust after abatement systems as a
"Nice to Have" feature.<br>
<br>
I believe that having detectors in the pump exhaust of a tool is Low
Priority and only confirms what you already know: if toxic stuff is
going into the system, toxic stuff is coming out too.<br>
<br>
However, beyond that prioritization, the immediate follow up
question is: how many detectors do you need. Particularly for the
breathing air sensors, the number and spatial density of them is an
important consideration.<br>
<br>
Let me give you the number of sensors that we have for a 10,000 Sq
Ft (1000 SqM) clean room facility:<br>
<br>
We have a total of about 120 gas sensors that directly
support/monitor this facility and about 25-30 more that support
other private laboratories. Of those 120 sensors, approximately 30
monitor gas cabinets and the 4 empty cabinets that we use for
in-bunker storage. Approximately 75 sensors are in the clean room
itself with about 50 of them monitoring exhausted enclosures
associated with individual tools and the remaining 25 monitor
breathing air close to places where that gas might be found.
Finally, we have 17 detectors in the sub-fab. Four of those monitor
VMBs or the one BCl3 cabinet that lives outside the bunker, 9
monitor breathing air, and four monitor for low oxygen (we don't
have LN2 down there, but we do have 2" distribution lines that could
deplete a lot of air if they ever ruptured.)<br>
<br>
Please let me know if you have any questions and I will looking
forward to reading the responses from a number of other facilities.<br>
<br>
Note: we probably have more gases that need detection than some
facilities. Our list of detected gases includes the hydrides
(silane, germane, diborane, arsine, and phosphine), DCS, chlorine,
hydrogen bromide, boron trichloride, anhydrous hydrogen chloride,
anhydrous hydogen fluoride, and ozone. Also, I should add that our
120 gas sensors probably includes 15-20 hydrogen detectors (we use
0-1000 ppm rather than LEL hydrogen sensors).<br>
<br>
Thanks,<br>
<br>
John<br>
<br>
<div class="moz-cite-prefix">On 2/11/2015 9:39 AM, Matthieu Nannini,
Dr. wrote:<br>
</div>
<blockquote
cite="mid:84DF1F10-9D58-4A5B-963E-FF5E755B2C35@mcgill.ca"
type="cite">
<meta http-equiv="Content-Type" content="text/html;
charset=windows-1252">
Colleagues, first thanks Vito for initiating this discussion. Very
important points where made which led me to explore the labnetwork
archives about sub-atmospheric setup and TGMS. Fore those
interested I will save you the search:
<div><a moz-do-not-send="true"
href="https://www-mtl.mit.edu/pipermail/labnetwork/2012-August/000541.html">https://www-mtl.mit.edu/pipermail/labnetwork/2012-August/000541.html</a></div>
<div><a moz-do-not-send="true"
href="https://www-mtl.mit.edu/pipermail/labnetwork/2013-August/001004.html">https://www-mtl.mit.edu/pipermail/labnetwork/2013-August/001004.html</a></div>
<div><a moz-do-not-send="true"
href="https://www-mtl.mit.edu/pipermail/labnetwork/2014-July/001346.html">https://www-mtl.mit.edu/pipermail/labnetwork/2014-July/001346.html</a></div>
<div><a moz-do-not-send="true"
href="https://www-mtl.mit.edu/pipermail/labnetwork/2013-August/000998.html">https://www-mtl.mit.edu/pipermail/labnetwork/2013-August/000998.html</a></div>
<div><br>
</div>
<div>Since we are in a gas discussion timing,</div>
<div>
<div><br>
</div>
<div>If you had to prioritize the following position of the
sensors, what would you recommend ?</div>
<div><br>
</div>
<div>- exhaust of gas cabinet</div>
<div>- gas cabinet at the tool</div>
<div>- VMB if any</div>
<div>- exhaust of pump after the tool ?</div>
<div>- exhaust after abatement system ?</div>
<div>- free space sensors scattered around most sensitive areas:
where human presence is usually high</div>
<div><br>
</div>
<div>Thanks</div>
<div><br>
</div>
<div>
<div apple-content-edited="true"><span
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-----------------------------------
<div>Matthieu Nannini<br>
McGill Nanotools Microfab<br>
Manager<br>
t: 514 398 3310<br>
c: 514 758 3311<br>
f: 514 398 8434<br>
<a moz-do-not-send="true"
href="http://mnm.physics.mcgill.ca/">http://mnm.physics.mcgill.ca/</a><br>
------------------------------------</div>
</div>
</span></div>
</span></span></div>
<br>
<div>
<div>Le 2015-02-11 à 10:53, Vito Logiudice <<a
moz-do-not-send="true"
href="mailto:vito.logiudice@uwaterloo.ca">vito.logiudice@uwaterloo.ca</a>>
a écrit :</div>
<br class="Apple-interchange-newline">
<blockquote type="cite">
<div style="word-wrap: break-word; -webkit-nbsp-mode:
space; -webkit-line-break: after-white-space; font-size:
15px; font-family: Calibri, sans-serif;">
<div>
<div>Hi Dennis,</div>
<div><br>
</div>
<div>Great insights – thanks very much for sharing.</div>
<div><br>
</div>
<div>Our aim is to avoid cold spots and keep the
entire system at 19C to 20C, especially since the
DCS line traverses a loading dock between the gas
bunker and the fab. The two roll-up dock doors are
equipped with heated air curtains but we wanted the
added insurance of a heated/insulated line. </div>
<div><br>
</div>
<div>In our particular case, we've got a single 120
foot line between the gas cabinet and the point of
use (no VMB's) and we did our best to stay true to
the use of large radius bends all along the run. The
DCS panel design was kept as simple as possible (no
regulator) and the entire cabinet is located in a
heated bunker in which temperature trends are
monitored.</div>
<div><br>
</div>
<div>Good point about the possible risk of fire. While
the heat trace controller is capable of outputting a
limited amount of power, we did see some odd "burn"
marks at some locations which lead us to conclude
that the Armaflex insulation's upper use limit of
105C may have been exceeded at some of the void
locations. In light of these findings we've decided
to use fiberglass insulation instead of Armaflex for
the repair.</div>
<div><br>
</div>
<div>Best,</div>
<div>Vito</div>
<div>
<div><br>
</div>
</div>
</div>
<span id="OLK_SRC_BODY_SECTION">
<div style="font-family: Calibri; font-size: 11pt;
text-align: left; border-width: 1pt medium medium;
border-style: solid none none; padding: 3pt 0in 0in;
border-top-color: rgb(181, 196, 223);">
<span style="font-weight:bold">From: </span>Dennis
Grimard <<a moz-do-not-send="true"
href="mailto:dgrimard@umich.edu">dgrimard@umich.edu</a>><br>
<span style="font-weight:bold">Date: </span>Tuesday,
10 February, 2015 10:32 PM<br>
<span style="font-weight:bold">To: </span>Vito
Logiudice <<a moz-do-not-send="true"
href="mailto:vito.logiudice@uwaterloo.ca">vito.logiudice@uwaterloo.ca</a>><br>
<span style="font-weight:bold">Cc: </span>Labnetwork
<<a moz-do-not-send="true"
href="mailto:labnetwork@mtl.mit.edu">labnetwork@mtl.mit.edu</a>><br>
<span style="font-weight:bold">Subject: </span>Re:
[labnetwork] Conclusion: Heat trace issues on DCS
gas lines<br>
</div>
<div><br>
</div>
<div>
<div dir="auto">
<div>Vito:</div>
<div><br>
</div>
<div>I have watched with great pleasure the
discussion on this topic. I too agree that much
good info has been discussed ... Great feedback
from some very knowledgable people indeed.</div>
<div><br>
</div>
<div>I need to throw a wrench in the discussion
(or prove my ignorance). I have always resisted
heat taping for the following reasons: 1) when
the tube enters a VMB or any ventilated
enclosure there is a significant temperature
drop due to the large purging flow rate within
the enclosure ... Tending to cool the line at
the worst possible point, 2) the VMB type
enclosures tend to have many right angle welds
and valves which promote condensation ....
Rather than long graceful bends typically used
external to the enclosure, 3) SS is a horrible
heat conductor ... As is n2 gas ... So if I heat
trace a double wall tube how much heat actually
gets to the inner tube? how consistent is that
heat? What is the temperature gradient?, and 4)
the actual cold to hot temperature gradient
(desired) is difficult to institute along the
length of line ... A good feedback loop is
required. Also, heat tape gives me the district
impression that it can contribute to an out of
control heating failure with a possible fire as
a result.</div>
<div><br>
</div>
<div>So, not that it solves your problem but here
is what I have tried to always implement: 1)
short runs (home runs not a distribution), 2)
minimum short radius right angles, 3) minimize
VMB's ... Mini gas cabinets with multiple
outputs in the cabinet, 4) chilled bottles, 5)
vacuum delivery, and 6) large radius bends.</div>
<div><br>
</div>
<div>Just food for thought ...<br>
<br>
Dennis S Grimard, Ph.D.
<div>Associate Director of Operations, MIT.nano</div>
<div><br>
</div>
<div>Massachusetts Institute of Technology</div>
<div>60 Vassor Street, Bldg 39-556</div>
<div>Cambridge, MA 02149</div>
<div><br>
</div>
<div>C: (734) 368-7172</div>
<div>EM: <a moz-do-not-send="true"
href="mailto:dgrimard@mit.edu">dgrimard@mit.edu</a></div>
</div>
<div><br>
On Feb 10, 2015, at 1:30 PM, Vito Logiudice <<a
moz-do-not-send="true"
href="mailto:vito.logiudice@uwaterloo.ca">vito.logiudice@uwaterloo.ca</a>>
wrote:<br>
<br>
</div>
<blockquote type="cite">
<div>
<div>
<div>Dear Colleagues,</div>
<div><br>
</div>
<div>Thank you very much to everyone whom
took the time to write in with their
insights on this issue. Special thanks to
John Shott and Tom Britton for the photos
and reference documents provided.</div>
<div><br>
</div>
<div>So that others may perhaps benefit from
our experience, we've concluded that the
cause of the premature failure appears to
have been the presence of several "voids"
where the heat trace was not in intimate
contact with the SS tubing. This occurred
even though the trace had been taped every
12 inches per the manufacturer's
recommendations. We also noted voids at
some elbows where maintaining contact
was/is difficult. </div>
<div><br>
</div>
<div>To keep the issue from repeating itself
in the future, our plan is to reinstall
two new heat traces along the length of
the tubing, one on the bottom and one on
the top. One of these will remain active
while the backup trace will be kept off
and act as an insurance policy should the
primary unit fail in the future. If anyone
sees a problem with this particular
approach, I would be glad to hear from
you.</div>
<div><br>
</div>
<div>In the new installation, conductive
putty will be used to fill any voids
before aluminum tape is applied along the
entire length of the line much like John
showed in his attached photo. The entire
assembly will then be re-insulated per the
original design specification.
Fortunately, the problem occurred under
warranty so our only out-of-pocket cost
will be limited to the cost of the backup
heat trace (a few hundred dollars).</div>
<div><br>
</div>
<div>Regards,</div>
<div>Vito</div>
</div>
<div><br>
</div>
<span id="OLK_SRC_BODY_SECTION">
<div style="font-family: Calibri; font-size:
11pt; text-align: left; border-width: 1pt
medium medium; border-style: solid none
none; padding: 3pt 0in 0in;
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<span style="font-weight:bold">From: </span>Vito
Logiudice <<a moz-do-not-send="true"
href="mailto:vito.logiudice@uwaterloo.ca">vito.logiudice@uwaterloo.ca</a>><br>
<span style="font-weight:bold">Date: </span>Wednesday,
21 January, 2015 12:23 PM<br>
<span style="font-weight:bold">To: </span>Labnetwork
<<a moz-do-not-send="true"
href="mailto:labnetwork@mtl.mit.edu">labnetwork@mtl.mit.edu</a>><br>
<span style="font-weight:bold">Subject: </span>[labnetwork]
Heat trace issues on DCS gas lines<br>
</div>
<div><br>
</div>
<div>
<div style="word-wrap: break-word;
-webkit-nbsp-mode: space;
-webkit-line-break: after-white-space;
font-size: 15px; font-family: Calibri,
sans-serif;">
<div>Dear Colleagues,</div>
<div><br>
</div>
<div>We are experiencing an issue with
the heat trace on our Dichlorosilane
gas line. The all-welded 1/4" SS line
is encapsulated with a 1/2" SS outer
containment line which is itself heat
traced with a single strand of heat
trace that runs the entire length of
the coax assembly. The 120 foot line
is insulated as shown in the attached
photo. A portion of the heat-trace
appears to have failed prematurely (it
was installed less than one year ago)
and we are wondering if the method of
installation may be the cause.</div>
<div><br>
</div>
<div>The heat trace was not installed in
a spiral fashion around the outer 1/2"
tube. Rather it was installed in a
straight fashion along its entire
length with "heat trace fastening
tape" located every four feet or so. A
member of my team has suggested that
such a straight rather than spiral
installation may have caused hot spots
(at the fastening locations) which may
have in turn caused the failure.</div>
<div><br>
</div>
<div>I would appreciate hearing from the
community on this point: Are the heat
traces around your low pressure gas
lines spiral-wound around the lines or
are they installed in a straight
fashion and somehow fastened along the
entire length?</div>
<div><br>
</div>
<div>Other insights/suggestions on the
proper heat tracing of gas lines by
experts in the field as well as
comments on possible causes of
premature heat trace failure are very
much welcome and appreciated. Thank
you.</div>
<div><br>
</div>
<div>Regards,</div>
<div>Vito</div>
<div>
<div><font class="Apple-style-span"><font
class="Apple-style-span"
style="font-size: 14px; "
face="Calibri"><font
face="Calibri,sans-serif">--</font></font></font></div>
<div><font class="Apple-style-span"><font
class="Apple-style-span"
style="font-size: 14px; "
face="Calibri"><font
face="Calibri,sans-serif">Vito
Logiudice </font>P.<font
face="Calibri,sans-serif">Eng.</font></font></font></div>
<div><font class="Apple-style-span"><font
class="Apple-style-span"
face="Calibri"><font
style="font-size: 14px; "
face="Calibri,sans-serif">Director
of Operations, Quantum NanoFab</font></font></font></div>
<div><font class="Apple-style-span"><font
class="Apple-style-span"
face="Calibri"><font
style="font-size: 14px; "
face="Calibri,sans-serif">University
of Waterloo</font></font></font></div>
<div><font class="Apple-style-span"><font
class="Apple-style-span"
face="Calibri"><font
style="font-size: 14px; "
face="Calibri,sans-serif">Lazaridis
QNC 1207</font></font></font></div>
<div><font class="Apple-style-span"><font
class="Apple-style-span"
face="Calibri"><font
style="font-size: 14px; "
face="Calibri,sans-serif">200
University Avenue West</font></font></font></div>
<div><font class="Apple-style-span"><font
class="Apple-style-span"
face="Calibri"><font
style="font-size: 14px; "
face="Calibri,sans-serif">Waterloo,
ON Canada N2L 3G1</font></font></font></div>
<div><font class="Apple-style-span"><font
class="Apple-style-span"
face="Calibri"><font
style="font-size: 14px; "
face="Calibri,sans-serif">Tel.:
(519) 888-4567 ext. 38703</font></font></font></div>
<div><span style="font-size: 14px; ">Email: <a
moz-do-not-send="true"
href="mailto:vito.logiudice@uwaterloo.ca">vito.logiudice@uwaterloo.ca</a></span></div>
<div><span style="font-size: 14px; ">Website: </span><a
moz-do-not-send="true"
href="https://fab.qnc.uwaterloo.ca/">https://fab.qnc.uwaterloo.ca</a></div>
<div><br>
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