Yesterday's toxic gas alarm ....

John Shott shott at stanford.edu
Fri Aug 6 11:29:59 PDT 2010


> 1.  Shouldn't we be filling out an SU-17B incident report in response 
> to my (and Gaurav's) exposure on Sunday?  I would classify the 
> incident as a "near-miss."
Yes, if you smelled anything you should file a report.  I never smelled 
anything so don't intend to.
>
> 2.  What is the specific exposure level for these gases on the MDA 
> that triggers a notification (either to work control, standby phone, 
> and the lab/building-wide alarm)?

There are two levels on the MDA system .... one that only shows up on 
the front panel and the other that talks to the main gas monitoring 
system, I believe.  The levels are different depending on whether it is 
a breathing air system.  If I am not mistaken the sensor that tripped 
the alarm yesterday was sensor D1 in the breathing air and is set to 
trigger the building alarm, shut down ALL toxic gases at the bottles, 
and calls the fire department.  That happens at 100 ppb concentration of 
either B2H2 or PH3.  I think that these detectors are equally sensitive 
to either of the dopants, but I need to confirm that.  I also don't know 
whether the MDA "phones home" if it sees that level once or whether it 
waits for a second confirming number.
>
>  According to the MSDS on the SNF website for the phosphine/silane gas 
> mixture (I do not know which particular mixture we were exposed too), 
> "detection of concentrations above 50% of the PEL of phosphine 
> (PEL=0.3ppm) should trigger immediate response and corrective action.  
> Detection of higher levels should initiate an alarm calling for 
> evacuation of all personnel with the potential to be exposed".
>
> While we did not reach above 0.3ppm (thank goodness) in the 
> maintenance hallway air (but we did in the exhaust lines), I think we 
> came close to the 50% level.  In this case, if a building-wide 
> evacuation is not called for, certainly some other notification should 
> have happened.  What is that notification chain, and did it fail?

I have not found that anything failed ... the fact that the process on 
Sunday was aborted likely caused the levels to fall before an alarm was 
triggered.
>
> 3.  It would seem prudent that we notify the lab community reminding 
> them of specific lessons learned during this incident.  I would be 
> happy to draft an e-mail about this.  I would point out the continued 
> vigilance that's necessary in the lab environment, encourage 
> labmembers to always be sensitive to any odd smells (and not be shy to 
> ask if others around them sense the same thing), and remind them the 
> type of odors associated with our toxic gas (for example, this 
> particular mixture came across as a garlic smell, and not the "fishy 
> smell" that's reported). On a side note if this was a phosphine/silane 
> mixture, perhaps the "fishy smell of phosphine"  + "sweet smell of 
> silane" = a garlic-like odor.
Has anyone ever smelled silane?  Being pyrophoric, it's not around for long.
>
> 4.  I was concerned when I came back in the lab Monday morning and saw 
> the "offending" furnace operational again, and released to lab users.  
> I went to coral in hopes of finding an explanation of what caused the 
> toxic gas release, but there was little detail.  I have to admit, that 
> did little to assure me that the problem was actually fixed.  Can you 
> explain what the theory behind that Monday morning fix was?  And 
> shouldn't it be on Coral?
Yes, documentation should have been better.  I had thought that it had 
been thoroughly investigated .... but clearly didn't resolve the problem.
>
> Thanks,
> Tom 

Short answers, I know, but I'm heading to the airport ... back Monday 
afternoon.

Thanks,

John




More information about the safety mailing list