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Code Question Exhausted Enclosure 2008-11-19
To All There has been confusion on this topic for a number of years. Ventilated enclosure has the same meaning as exhausted enclosure. The problem is definition, ventilation means air movement, one can have a fan inside an enclosure moving the air around and it is ventilated. What the codes really wanted was air be constantly drawn out of the enclosure to a abatement device or a vent stack. In recent years there has been a move to replace ventilated enclosure to exhausted enclosure. Larry Fluer has been championing this effort and he said he missed the following 2 in the 2006 IFC
2703.2.2.2 Additional regulations for supply piping for health-hazard materials. Supply piping and tubing for gases and liquids having a health-hazard ranking of 3 or 4 in accordance with NFPA704 shall be in accordance with ASME B31.3 and the following:
1. Piping and tubing utilized for the transmission of highly toxic, toxic or highly volatile corrosive liquids and gases shall have welded, threaded or flanged connections throughout except for connections located within a ventilated enclosure if the material is a gas, or an approved method of drainage or containment is provided for connections if the material is a liquid.
3704.2.2.7 Treatment systems. The exhaust ventilation from gas cabinets, exhausted enclosures, gas rooms and local exhaust systems required in Sections 3704.2.2.4 and 3704.2.2.5 shall be directed to a treatment system.
2.2. An approved automatic-closing fail-safe valve located immediately adjacent to cylinder or portable tank valves. The fail-safe valve shall close when gas is detected at the PEL by a gas detection system monitoring the exhaust system at the point of discharge from the gas cabinet, exhausted enclosure, ventilated enclosure or gas room. The gas detection system shall comply with Section 3704.2.2.10.
NFPA 55 defines an exhausted enclosure to be the following. It is the same definition as in the IFC. There are no instances where ventilated enclosure is used
3.3.36* Exhausted Enclosure. An appliance or piece of equipment that consists of a top, a back, and two sides that provides a means of local exhaust for capturing gases, fumes, vapors, and mists.
A.3.3.36 Exhausted Enclosure. Such enclosures include laboratory hoods, exhaust fume hoods, and similar appliances and equipment used to retain and exhaust locally the gases, fumes, vapors, and mists that could be released. Rooms or areas provided with general ventilation, in and of themselves, are not exhausted enclosures.
Hope this helps Eugene Ngai
Sent: Wednesday, November 19, 2008 4:55 PM To: SEMI EHS Grapevine Subject: Code Question SEMI Environmental Health & Safety Grapevine
What is the difference between an exhausted enclosure and a ventilated enclosure or are they the same according to building and fire codes? Thanks in advance for any insight you can provide. Bob
Leak detection - vacuum pumps/exhaust connections. 2008-07-07
Most of the fluorinated compounds have a thermal conductivity much less than air so it will be very sensitive. Just need to make sure that the air flow to the detector is not interrupted, otherwise you'll get a false positive
Eugene
Sent: Monday, July 07, 2008 1:13 PM To: SEMI EHS Grapevine Subject: Leak detection - vacuum pumps/exhaust connections. SEMI Environmental Health & Safety Grapevine
Does anybody have any experience with a simple hand-held device that is capable of detecting leaks from vacuum pumps and exhaust lines associated with CVD equipment running chamber cleans (NF3 remote plasma recipes generate various fluorinated species during the clean cycle). I realize one could use more sophisticated gas detection equipment commonly used for ERT purposes but often this equipment is not very portable or best suited for pinpointing an exhaust line leak downstream of a pump for example. In this application, there is really no need for quantification but rather just to determine if there is a leak at a fitting/connection or an O-ring misalignment, etc. I was wondering if a simple refrigerant leak detection device would be cross sensitive to the by-products and be suitable. Has anyone tackled this one before? Thanks in advance.
Regards, Peter
Nitrogen inerting to gas box & VMB? 2005-09-26
I agree with Steve's comments. In release testing that we did with a Trimethylaluminum cabinet this year, we could not easily seal the cabinet without putting on new door seals and foaming all of the cabinet penetrations.Even after all this, the door latch leaked a lot of air. Flooding the cabinet with N2 created a lot of noise and high N2 flow rates Eugene Ngai
Sent: Monday, September 26, 2005 4:03 PM To: SEHS Grapevine Subject: RE: Nitrogen inerting to gas box & VMB? SEMICONDUCTOR INDUSTRY ENVIRONMENTAL HEALTH & SAFETY (SEHS) GRAPEVINE
John I've never seen that done specifically for gas boxes or vmbs, nor would I recommend it. If you're inerting a gas box or vmb you'd obviously need some continuous flow of N2 to keep the box purged. If the box were fairly tightly sealed that could be a relatively low flow rate, but the gas boxes and vmbs I've seen all have a considerable amount of openings included in their design since they universally are exhausted. And if you tried to combine exhaust and inerting you'd have to supply an impractical amount of inert gas to accomplish anything.
Besides that, you still have the problem of what happens to any flammable gas that does leak. Unless you have an enclosure that is designed to contain the full, line pressure of the flammable gas in pressure (never seen such a thing), you'd have to have somewhere for the gas to go. And if you don't have exhaust, that somewhere is the room containing the enclosure. That's the benefit of continuous exhaust ventilation on flammable gas enclosures. If there is a leak, it is carried out of the area and as you indicated, done so with so much excess air flow that you keep the flammable gas / air mixture (hopefully) below LEL. Steve Van Tassell
Sent: Monday, September 26, 2005 12:48 PM To: SEHS Grapevine Subject: Nitrogen inerting to gas box & VMB? SEMICONDUCTOR INDUSTRY ENVIRONMENTAL HEALTH & SAFETY (SEHS) GRAPEVINE
I have a question regarding gas boxes and VMBs within which there could be a leak of flammable gas. I believe that the standard engineering control is to apply extract ventilation at a rate which prevents escape of the gas into the surrounding environment, and which will reduce gas concentrations to a fraction of the LEL. The latter is particularly important where ignition sources may be present in the box. As an alternative to these high rates of ventilation to mitigate against an explosive atmosphere has any one used a continuous nitrogen purge to exclude air?
If so are there any standards that apply and/or what advice would you give, for example what N2 flowrate is require? Would you allow positive pressure in the (inert) Gas Box or VMB so that air could not be drawn in under any circumstances, or ensure that it is still connected to an extract which maintains a slight negative pressure in the box? Would the box be completely sealed to prevent the ingress of air? Sorry to ask what may be fairly basic questions but this in not my specialist field.
Thanks for any suggestions or references that may be forthcoming.
Best regards John
Pyrophoric Foreline 2006-03-01
Since there is a major safety issue involving the removal of process tool forelines when these forelines are heavily contaminated with pyrophoric residue, the protection of the individual along with the protection of the surrounding area become an issue for emergency response personnel. Therefore, this discussion thread is being mirrored in the SERF Discussion Groups under the thread “Gas Systems: Silane Incident with Fatality, Nov 2005.”
Follow this link directly to the Forum: http://seshaonline.org/serf/bb.php3
Best Regards, Bob Barnes
Sent: Wednesday, March 01, 2006 6:57 AM To: SEHS Grapevine Subject: Pyrophoric Foreline SEMICONDUCTOR INDUSTRY ENVIRONMENTAL HEALTH & SAFETY (SEHS) GRAPEVINE
To All I am posting this for Chuck who is having a problem with this coming out garbled
I am looking for best practices for removing process tool forelines when these forelines are heavily contaminated with pyrophoric residue, such as that when the process utilizes Silane. We have used a couple of different methods which have been somewhat successful, but I am sure that the experience represented by those on this forum will be helpful.
Regards, Chuck
Eugene Ngai
Trace heating to coaxial gas lines - industry practice to minimize heat loss? 2005-11-02
Both, depends on the Fab None of the below are pyrophoric. There are many others that are (TMAl, SiH4, Disilane, DCS, B2H6) Eugene
Sent: Wednesday, November 02, 2005 4:03 PM To: SEHS Grapevine Subject: RE: Trace heating to coaxial gas lines - industry practice to minimize heat loss? SEMICONDUCTOR INDUSTRY ENVIRONMENTAL HEALTH & SAFETY (SEHS) GRAPEVINE
Thanks Eugene: is this chemical handling generally done in Clean Room areas or outside of them? Also are any of these chemicals pyrophoric, and if so are there special protective garments in use to protect from both chemical and flame hazard at once?
Randall D. Templeton
Ngai,Eugene Y11/02/05 01:51 PM Subject RE: Trace heating to coaxial gas lines - industry practice to minimize heat loss? SEMICONDUCTOR INDUSTRY ENVIRONMENTAL HEALTH & SAFETY (SEHS) GRAPEVINE
Yes, as corrosive materials, the minimum PPE will be faceshields and chemical resistant coveralls when changing these containers. Some Fabs require SCBA also Eugene
From: Randy D Templeton [mailto:Randy.D.Templeton@can.dupont.com] Sent: Wednesday, November 02, 2005 12:19 PM To: SEHS Grapevine Subject: RE: Trace heating to coaxial gas lines - industry practice to minimize heat loss? SEMICONDUCTOR INDUSTRY ENVIRONMENTAL HEALTH & SAFETY (SEHS) GRAPEVINE
Ngai, John: these chemicals seem to be fairly hazardous. I'm curious to know the personal protection that is used in handling these materials. Is it typical to wear protective coveralls, face shields etc. when handling them? Thank you. Randall D. Templeton
"Ngai,Eugene Y11/01/05 09:16 PM Subject RE: Trace heating to coaxial gas lines - industry practice to minimize heat loss? SEMICONDUCTOR INDUSTRY ENVIRONMENTAL HEALTH & SAFETY (SEHS) GRAPEVINE
John Please be aware that BCl3 is a low pressure liquefied gas with a boiling point of 55F and a vapor pressure of 19.9 psia while the SiCl4 is a liquid with a boiling point of 136 F and a vapor pressure of 3.9 psia so they will be dispensed differently.
BCl3 will be in a compressed gas cylinder and 100% of the gas will exit the cylinder at the low vapor pressure as a fully saturated gas. If there is high usage the pressure of the cylinder will decay rapidly due to the latent heat of vaporization. Many users heat the cylinder to compensate for this. If the tubing sees a temperature even 1 degree less, the BCl3 will liquefy in the lines, causing numerous problems. I know of at least 2 companies in the last year who have liquefied ClF3 in their lines due to this. In one case they filled 120 feet of tubing with liquid ClF3 and had an interesting experience when they tried to vent this.
SiCl4 will be in a container which will have a vapor and liquid line. Pure SiCl4 will not flow out of the container since it has a vapor pressure well below an atmosphere. Many sites bubble Nitrogen, Argon or Hydrogen through the diptube to saturate the vapor. To provide a steady concentration, the container must be temperature controlled to maintain a constant vapor pressure. In the tubing slight changes in temperature will also condense it out.
In both cases the container and tubing temperature must be controlled to prevent condensation.
Eugene Ngai
Sent: Tuesday, November 01, 2005 11:26 AM To: SEHS Grapevine Subject: Trace heating to coaxial gas lines - industry practice to minimise heat loss? SEMICONDUCTOR INDUSTRY ENVIRONMENTAL HEALTH & SAFETY (SEHS) GRAPEVINE
We plan to locate cylinders of BCl3 & SiCl4 in external gas cabinets and understand that we will need to trace-heat both the cylinder and the distribution lines. However, we also want the supply lines to be co-axial with a nitrogen purge for the annulus. We can see that the trace-heating of the co-axial lines will be extremely inefficient as the nitrogen flow will take the heat away.
What is the industry practice for this situation?
Thanks for all feedback given.
Best regards John
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