"The Seattle Police Athletic Association had to place a 55 gallon drum filled with sand outside the range office so guns would no longer be discharged in the office. The sign read: "Decock guns here"."
This doesn't sound right on a couple of points, I've never had a decocker fire a round on my Sigs P226, P229. That being said...
Seattle PD's Primary Duty Firearms are:
Glock Model 17or 19, 9mm
Glock Model 22 or 23, .40 S&W
Glock Model 21SF or 30SF, .45ACP
Special Duty (Plain Clothes) are:
Glock Model 26, 9mm
Glock Model 27, .40 S&W
Glock Model 30SF, .45ACP
Glock Model 43, 9mm
Department-approved 2-inch revolver
There are other allowed (approved) firearms, but the majority I see are Glocks, and certainly not enough to create a decocker malfunction epidemic.
https://www.seattle.gov/Documents/Departments/Police/manual/09_030_ERC_Feb2016.pdf
For the OP, the P320 has had a manual safety version available (in catalog), for some time, but they just started hitting the street this last Fall.