Workers need to enter a below-ground, concrete-lined vault to repair a leaking valve that controls the flow of wastewater from several buildings at your plant. The opening for the pit is outdoors and secured with a 36-inch diameter manhole cover. The pit is 12 feet deep, and the walls are 6 feet x 6 feet wide. The valve is at the bottom of the vault. You opened the cover, tested the atmosphere, and found oxygen levels to be at 16%. No toxic substances were detected. After ventilating the space for 15 minutes, the oxygen reading reached 18% and remained at that level.

Workers need to enter a below-ground, concrete-lined vault to repair a leaking valve that controls the flow of wastewater from several buildings at your plant. The opening for the pit is outdoors and secured with a 36-inch diameter manhole cover. The pit is 12 feet deep, and the walls are 6 feet x 6 feet wide. The valve is at the bottom of the vault. You opened the cover, tested the atmosphere, and found oxygen levels to be at 16%. No toxic substances were detected. After ventilating the space for 15 minutes, the oxygen reading reached 18% and remained at that level.

Address the following items:

Using the flow chart in Appendix A of 29 CFR 1910.146, determine the classification of the space. Explain how you reached the decision.
Based on your determination, develop an OSHA-compliant standard operating procedure (SOP) for workers to follow when entering the space to repair the valve. Include the citation(s) from 29 CFR 1910.146 for each step of the procedure.