The floor area of 5200 ft2 with a ceiling height of 20 feet was designed to simultaneously repair 6 trucks. The HVAC system was designed to ensure that the CO/NOx concentration in the space was not to exceed 25 ppm (CO) / 3 ppm (NOX) for Threshold Limit Values for a safe working environment as per ACGIH guidelines.
Calculations yielded that a 4000 cfm (0.75 cfm/ft2) make up air unit and exhaust fan with provisions for source capture of the contaminant directly from the exhaust tail pipe of the trucks would be sufficient to maintain the space at safe levels. Our calculations yielded that if there were a release of 5 ft^3 of CO into the space (30 seconds of tail pipe exhaust from 6 trucks released into the space without source capture) the space could be normalized to acceptable levels within 17 minutes of system run time.
We also designed the plumbing system with sediment, sand and grit, fats, oil and grease interception by means of two sloped linear trench drains feeding into a single compartment sump and two compartment sump respectively. The single compartment sump was connected to the two compartment sump with a 4 " PVC pipe. The two compartment sump was retrofitted with a dip pipe to ensure that the liquid discharged into the sanitary system was being pulled from the lower strata of the fluid bank, ensuring an effective level of oil and grease interception. Upon being challenged by the authority having jurisdiction that our retrofit wouldn’t be CSA approved, we proved to the authority having jurisdiction that there was no CSA standard for oil interceptors involving gasolines as found in a repair garage and our argument was approved.
References: ASHRAE 62.1, NFPA 55, NPC-2015