The target cells themselves represent the most likely failure point
in the hydrogen system. The outer walls and downstream window
of the cells are made of
0.03 to 0.045 
thick 3004 aluminum (Coors beer cans in a former
incarnation) (all the final ones are above 0.035 ).
There are two cells soldered to each cell block, one 15 
long
and one 4 long. Both cells have an outer diameter of
approximately 2.5 inches.
The upstream windows of the cells are made from 0.0028 thick 5052
aluminum.
These windows are soldered to 1.75 diameter (0.065 wall)
upstream window tubes which are in turn soldered to the cell block.
Since all the components are made of aluminum it is necessary to plate them before soldering. The final components were copper plated before assembly.
The cell block components have been pressure tested hydrostatically at Jefferson Lab. We chose the thinnest beer cans for the pressure burst test. Results are listed in the summary table. Upstream windows have been tested to similar pressures. Finally, the entire completed cell block assemblies were pressurized to 85 PSID with helium gas. A summary of the testing program to date is presented in Table 3.1.