Re: [Phys-l] operating room physics

[Brian Whatcott <betwys1@sbcglobal.net>]

Anthony Lapinski wrote:
> I'm teaching electricity soon. We often see doctors wearing blue plastic
> covers for their shoes, mainly to prevent dirt/dust from entering the room
> from the outside. These covers appear to be insulating. However, I read in
> a physics book years ago that medical shoes/covers should be conducting so
> that any static charge doctors may acquire will be discharged into the
> floor. This is important so that a spark is not created in the presence of
> oxygen gas used during an operation.
>
> I am a a bit confused with all of this. Do these shoe covers have metal
> screens in them or something? Or is the spark risk very low?
>
>   
People who work in potentially explosive environments (like you!)  
receive design attention
to avoid spark production. Gas can caps and fuel tank lids are selected 
from non-sparking
combinations.   Hammers are cast or wrought in bronze rather than steel, 
and live sparks
and flames are guarded under twin metal gauze shields to avoid flame 
propagation in mines.

Environments with bulk fine powders are an unexpected hazard. Bulk 
carriers have seen
exlposions when pumping powder cargoes. I recall that Mythbusters have 
demonstrated
the potential of wheat flour etc., in improvised cannons.

When trucks refuel aircraft, the first step is clipping on the grounding 
strap connecting
bowser and airframe.

   Technicians working with modern semiconductor devices like MOSFET
(metal oxide-silicon field effect transistor) chips are equipped with 
conductive
plastic bracelets with a flying lead to a work surface to  avoid 
destroying the very
thin insulating layers supporting electric effect gates even though 
these gates are
usually given back to back diodes to hold down volt spikes.

For the plastic floors in operating rooms, it is important to provide 
the right level of
conductivity too, which is typically in the tens of megohms up.

Static-protected plastic bags are in universal use to carry 
semi-conductor devices.
These are often tinted for ready recognition.  Too much conductivity is 
hazardous
too in that it can support lethal stray currents.

Brian W