A year or so after completing my project, I followed up with some of the firefighters at Station 8 about how the dryers had fared. Their response: there had been no difficulties with dryer 2, while dryer 1 had managed to burn out two air blowers and was out of of commission when I visited.
Modifications made to dryer 2 by firefighters include drilling holes through the top 1.5-inch portions of piping to allow for better drying of jackets, as well as adding wooden extenders to the bottom 3-inch pipes to enable better drying of pants. This extension can be easily done with a dowel or other long skinny piece of lumber and a couple of screws. Simply predrill through the PVC and use 4 or 5 screw to attach the dowel to the pipe. Thanks to GFR for these cool upgrade ideas!
One firefighter I talked with hypothesized the reason for Dryer 1's issue with breaking air blowers: as dryer 1 has valves that allow for increased pressurization, it was a common occurrence for all but one valve to be closed (in order to dry a suit faster), and with such a small air release point, the pressure frequently built up to a level which eventually broke the air blower. This makes sense, as dryer 1 uses a weaker blower than dryer 2, though experiences greater pressurization.
Solutions include, but are not limited to:
Signage. Simply make a label that two or more valves should be left on when the dryer is running.
Removing the valves from the design. This can be done partially (2 hangers with valves and 2 without), or completely.
Installing an automatic pressure release valve.
A thermometer that signals overheating. The temperature of a container increases with pressure (Gay Lussac's Law), so a high temperature inside the dryer would correlate to strain on the blower.
Using 1.5-inch pipes for the hangers instead of 1-inch, and drilling bigger or a greater number of holes. This would decrease pressure somewhat.
The most efficient, successful solutions will result from knowledge about what pressures are damaging to the air blower you decide to use.
I hope this exploration of issues encountered later in the life of these dryers was useful . Best of luck to you!