Re: H-3 Exit Signs

[jatalbq@ix.netcom.com (Joseph A Tompkins )]

Over the last two and half years I have been involved in a program to 
remove tritium powered radioluminescent airfield lighting units from 
the State of Alaska.  These units totaled over a quarter of a mega 
curie of activity and are very similar in design to exit signs. 

We had 12 - 15 units that had been broken, with releases ranging from 
50 - 350 curies of activity.  The gase from a broken tube dissipates 
very rapidly and unless you are in a small sealed room with few 
airchanges there is little risk.  This situation changes if the units 
casing has lost integrity.  The phosphor powder from these tubes is 
highly contaminated with tritium and provides a ready path for 
inhalation or ingestion.  Our total dose from handling these large 
broken units was less than ten mRem CEDE.

The condition of an exit sign with intact casing and broken tubes could 
potentially give an individual a few mRem of CEDE. The situation where 
the casing is totally destroyed and phosphor liberally distributed over 
a site and the individuals present, would typically give doses of a few 
hundred mRem for the largest tritium powered lighting units (990 Ci).  
The incident Bob Walker from AECB mentioned, involved about six units 
which originally contained 640 Ci each and which were dissassembled and 
systematically destroyed.  It would seem that an exit sign with only 20 
Ci of tritium at the outset would pose a much lower risk to any 
individual present.

The risk of using these devices in a facility is not so much whether 
you have one leaking tube in a device.  The much greater risk is 
associated with whether there is a potential for heavy equipment or 
aircraft to runover the unit and destroy the casing.  Unless your 
University library is much different from ours here in Albuquerque, I 
doubt these conditions exist.