Can Oxygen tanks work as a backup for not having an air filtration system in a bomb shelter? ume 2 days.?

Will be a cheap "work around" shelter dug in the dirt about 8 feet deep, polls on corners, netting covered by poly to keep from cave in. floor w/ 3 inches of rocks. The roof will be boards covered w/ 1.5 feet of dirt. Size 6 x 4 x 8. Basically, just want something to work for 48 to 72 hours of nuclear fallout.