good info! thanksI'm glad to hear you are doing it right. The cost is high but this is the right way to do it. That 80fpm spec is backed by the NRA in their indoor range design publication, which itself comes from the US military specification for ranges.
This is almost the exact same system that we did with the RCMP training academy ranges in Regina.
Occasionally some users do gripe about the unwanted breeze coming up behind them (I personally like it) but people need to remember that these ventilation systems are not installed for the comfort of the shooters. First and foremost they were designed for OH&S reasons. While a recreation shooter is only in the range occasionally and voluntarily and risk very little lead exposure, the people who actually work at the range are there many hours a day, day in day out. Their safety is more important than the shooter's comfort.
For those curious where the 80fpm number comes from, it is sort of interesting and it definitely wasn't pulled out of a hat.
The ideal minimum is 75fpm across the firing line (typically supplied by a pressurized perforated plenum wall behind the shooters). The air velocity must be maintained at around 30fpm for at least half way down the range before it reaches the bullet trap and the air must remain turbulence free. If the air velocity is too low or if there is too much turbulence the lead dust will begin to quickly accumulate on the floor. This is another hazard if there is no motorized target retrieval system and users track the dust back to the shooting line. Even with adequate ventilation you still need frequent wet mopping of the floor and a respirator should be worn by staff when cleaning up around the bullet traps.
Long story short, lead is no joke. I am glad to hear you are doing the right thing for you and your staff.
No one wants to see a repeat of the incident at Wade's Eastside Guns back in 2012 (46 people severely poisoned, including families of people who worked there).