Let's talk a little about troubleshooting existing systems. A major complaint is a lack of sufficient air flow into the hood. Look for plugged or dented ducts. Or crimped or damaged ducts. Or slipping fan belts or the fan turning in the wrong direction. Or worn out fan blades. Or misadjusted gates and dampers in the system. Or a clogged air cleaner. When constant plugging of ducts is the problem, check the transport velocity. Is it adequate to prevent settling? If employees complained about the hood or refused to use it, check to see if the hood interferes with work, or perhaps the hood just doesn't do the job of providing good emission control.
All ventilation systems require maintenance. A good maintenance program consists of: first, a written program; second, a good recordkeeping system to store drawings, plans, specifications, modifications, operating instructions, monitoring and testing results, and so forth; third, a good program provides for regular testing and inspection of the system. Checklists can help. One is provided in the handout materials included with this program.
All good ventilation systems are built to recognized standards. Some standards are mandatory, such as those found in the OSHA regulations and fire and building codes. Others are consensus or suggested standards. OSHA maintains a list of appropriate codes and standards. OSHA's permissible exposure limits (PELs) limit airborne concentrations of chemicals to which employees may be exposed and are found in 29 CFR 1910, subpart Z, of the OSHA regulations. OSHA's ventilation standard, 29 CFR 1910.94, also provides construction and operating guidelines for ventilation of open surface tanks, spray finishing operations, grinding, polishing, and buffing operations, and abrasive blasting. Other OSHA regulations provide ventilation requirements for welding, confined spaces, sawmills, and chemical storage facilities.
Remember, ventilation is only one way of protecting workers from exposure to air contaminants. However, it is one of the most important engineering control techniques for improving or maintaining the quality of the air in the occupational work environment.