A manufacturer described large product heating and aging furnaces fired by natural gas at 700°F to 2,200°F, ranging from 8x8x8 feet up to 18x18x18 feet, with remotely actuated doors. The hearths sit 22 to 29 inches above the building floor, and parts are loaded and unloaded by forklift. The company asked whether these furnaces are confined spaces when entry only requires stepping up from the floor to the hearth.
OSHA said yes, the furnaces meet the confined space definition (29 CFR 1910.146). Hearth heights of 22-29 inches require more than one step — OSHA referenced the 9.5-inch riser figure tied to stair requirements (29 CFR 1910.25(c)(3)) — which constitutes restricted entry. On top of that, because the doors are remotely actuated, employees cannot exit without restriction, satisfying the definition's limited-means-of-entry-and-exit element.
Asked whether there is a threshold height (such as 30 inches) that determines when access is 'restricted,' OSHA didn't set a bright line. It explained that spaces requiring special means of access such as ladders, and temporary, movable, spiral, or articulated stairs have limited egress, and that entry requiring multiple steps exceeding 9.5 inches likely qualifies as restricted.
Finally, adding a small access stool doesn't cure the problem — OSHA said stool-assisted entry would likely mean the space has a limited or restricted means for entry or exit, the same conclusion as for multi-step entry.