The (seems to be .. I didn't measure it) 16" pipe, approx 20 ft joints are set in place by a suction crane (I at first thought it was electro mag .. ) and the guy said it was a 30 lb "suction"
THAT should put some perspective on .. 30 lb.
No suction can be more than about 14.7 lbs/in2 unless you’re diving under pressure.
Ususally if you see a 30 when it comes to vacuum its a unit of measure with water in a glass tube, many of the air ducts I build have to withstand 30” of water in the vacuum tests before they collapse.