Update on yesterday's lab evacuation

Dear Labmembers:

As many of you may be aware, there was an an evacuation of the lab
yesterday around 4:30 pm for a chlorine-like smell. Thankfully,
everyone got out in an orderly fashion and there were no injuries.
After about 30 minutes, the lab air had cleared sufficiently so that
everyone was let back in.

Incident Response Team members (John, Jim H, Maurice, Gary) determined
that the smell was coming from the wbgen2 bench, near the tylan
oxidation furnaces. Subsequent follow-up determined the following:

1. A labmember was decontaminating labware in the dump rinser.
2. The labmember was using 1:1 concentrated HCl to hydrogen peroxide
(no water).
3. The exhaust on the system was at 0.5" (spec is that the bench should
not be operated when 0.5" or below.)

Normally, decontamination is done using a 5:1:1 ratio of water:HCl:H2O2
or 1:1:1, depending on the need. However, heat of mixing 38% HCl
directly with H2O2 (without sufficient water) results a highly heated
solution -- high enough that there was visible smoke coming from the
dump rinser (remember: hydrogen chloride is a gas at room
temperature). Now, the dump rinser, like most in the lab, is located
slightly in front of the red line behind which exhaust is highest.
During normal operation, the location is not a problem, since cassettes
and wafers to be rinsed carry a limited amount of acid and there is
sufficient exhaust to handle this. However, the dump rinse is clearly
not exhausted well enough to accommodate a gas-generating reaction,
particularly when the exhaust at this station was a hair below spec.

We are determined that this type of incident should NOT happen again.
To ensure this, we will be doing the following:

1. Tightening up our procedures for decontamination of labware and
contaminated stations (to resolve any confusion over appropriate
procedures.)
2. Better establishing the exhaust requirements for each bench (the
current lower limit does not appear to have enough margin for
accidents.) Each station will be audited and there will be
procedural/equipment changes to prevent use with insufficient exhaust.
3. Ensuring that wet bench users are fully aware of these procedures.

If you are a wet bench user, please be prepared for changes in coming weeks.

Thanks for your attention.

Your SNF Staff

--
Mary X. Tang, Ph.D.
Stanford Nanofabrication Facility
CIS Room 136, Mail Code 4070
Stanford, CA 94305
(650)723-9980
mtang@stanford.edu
http://snf.stanford.edu