remember to provide protection for those handling materials collected from the air cleaner most users install monitors on the air cleaner to warn when the air cleaner is not functioning properly when choosing a fan be sure to select one which will provide the necessary steady pressure and volume flow rate
remember though the volume flow rate is always determined by a mission control requirement
at the hood the fan is to serve the hood need not vice versa fans are divided into two main classifications
centrifugal in which the airflow is at right angles to the axis of rotation of the rotor and axial in which the airflow is parallel to the axis of rotation the rotor centrifugal fans are mostly used in local exhaust systems the two important types are the radio blade can and the backward inclined to blade fan the radio blade fan is the work or so the dust control industry because it is self-cleaning rugged in simple unfortunately it is any patient and noisy the backward inclined blade blade fan is quieter more efficient and less likely to overload the motor at high volume flow rate unfortunately it tends to clog or abraded when the exhaust air is laden with particulate material the axial fan is used to move large volumes of their against small static pressures it is often used in dilution ventilation systems and is usually no easier than equivalent centrifugal fans stack should be tall enough to ensure that contaminants are adequately dispersed into the atmosphere stack exit velocity should be about 3000 feet per minute
one ruler from is that the top of the stack should be at least 10 feet above the adjacent roof line or air intake if either are with 50 feet of the stack this will help avoid reentry mentally exhausted contaminants into the building rain protection is often used this illustration shows a slightly larger diameter docked mounted on the exhaust back rain never falls exactly straight down so when it this inside of the larger docked it drips down outside the stack to avoid the entrainment don’t use the slanted rain cap if the stack is close to the air intake for the building let,s talk a little about troubleshooting existing systems a major complaint is a lack of sufficient airflow into the hoot look for plugged or dented ducts or crimped or damage ducks or slipping fan belts or the fan turning in the wrong in the wrong direction or worn-out fan blades or miss adjusted gates and dampers in the system
or a clogged air cleaner when constant plugging a ducts is the problem check to transport velocity is it adequate to prevent settling if employees complain a about the hood or refuse 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 so first
a written program second a good record keeping system to store drawings plans specification modifications operating instructions monitoring and testing results and so forth third a good program provides for regular testing an inspection at 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 in fire and building codes others are consensus or suggested standards the handout materials a list appropriate codes and standards we have already mentioned ocean permissible exposure limits the PL,s limit airborne concentrations of chemicals to which employees may be exposed and are found in 29 CFR 1910 subpart Z up the OSHA regulations
Oj,s Ventilation standard 29 CFR 1910 point 94 also provides construction and operating guidelines for ventilation open surplus tanks spray finishing operations grinding polishing and pumping operations
and abrasive blasting other osha regulations provide Ventilation requirements for welding confined spaces sawmills and chemical storage facilities if you would like more information about Osho or about how to comply with osha ventilation regulations contact your nearest osha area of us home
this program has presented a practical overview up industrial revelation the handout materials provided with this program summarize and expand on the presentation 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.