The purpose of most ventilation systems is to prevent worker inhalation of contaminants. Specific points to consider during any investigation of a ventilation system include emission source, air behavior, and employee involvement. Slot Velocity The average velocity of air through a slot. Atmospheric pressure at standard conditions is 407 in. For example, are filters loaded or clean? Workers need to be trained in the purpose and functions of the ventilation system.
Generally, exhaust systems are interlocked with a dedicated make-up air system. Check dimensions and lengths with a ruler or a scale to be sure that this is the case. It sets standards for ducts and duct installation. Different types of air cleaners are made to remove particulates e. Volatile Organic or Reactive Chemicals If an organic or reactive chemical e. If the tapping produces heavy, thudding sounds and no sheet metal vibration, liquids or settled dust may be in the duct. Reducing the amount of contaminants generated or released from the process reduces ventilation requirements.
The correct amount of air should be supplied to the space. Users must request such authorization from the sponsor of the linked Web site. Local exhaust ventilation is designed to capture an emitted contaminant at or near its source, before the contaminant has a chance to disperse into the workplace air. Make-up Air Systems Exhaust ventilation systems require the replacement of exhausted air. In some cases the employer may wish to seek the services of an experienced professional ventilation engineer to assist in the data gathering. Measurements can be made with measuring tape.
Air Density The weight of air in lbs per cubic foot. Manometer A device that measures pressure difference; usually a U-shaped glass tube containing water or mercury. This section of the manual addresses ventilation in commercial buildings and industrial facilities. Please click the button below to continue. Historically, air-conditioning has been used in industry to improve or protect machinery, products, and processes.
At two duct diameters from the hood opening, capture velocity decreases by a factor of 10, to 30 fpm. These problems are caused by poor design, open access doors close to the fan, fan problems, or other problems. Smoking policies should include provisions for dedicated smoking areas. If a duct is constructed of 2½ or 4-foot sections, the sections can be counted elbows and tees should be included in the length. Are variable-flow devices like dampers, variable-frequency drives, or inlet vanes in use? Some systems are designed to provide individual control of rooms in a multiple-zone system.
To measure the duct, the tape should be thrown around the duct to obtain the duct circumference, and the number should be divided by 3. Where used, recirculation should incorporate air cleaners, a by-pass or auxiliary exhaust system, regular maintenance and inspection, and devices to monitor system performance. Regular maintenance of air cleaners increases their efficiency and minimizes worker exposure. . Industrial Ventilation, a Manual of Recommended Practice.
Hoods should never increase the likelihood of mechanical injury by interfering with a worker's freedom to move around machinery. What is to be included and why? Laminar Flow also Streamline Flow Air flow in which air molecules travel parallel to all other molecules; laminar flow is characterized by the absence of turbulence. In some instances the contaminant source may be the outside air. Equipment Operability Before taking velocity or pressure measurements, note and record the operating status of the equipment. Avoid designs that require that the velocities through some openings be very high in order to develop the minimum acceptable velocity through other openings or parts of the hood. The hood interferes with work The hood provides poor control of contaminants.
The presence of mold or slime is a possible sign of trouble. Air-conditioning has come to include any process that modifies the air for a work or living space: heating or cooling, humidity control, and air cleaning. However, manometers rarely can be used for velocities less than 800 fpm i. Employee training is not adequate. Although the initial costs of air conditioning are high, annual costs may account only for about 1% to 5% of total annual operating expenses.
The majority of the loss usually is associated with a vena contracta formed in the duct. If make-up air is not provided, a slight negative pressure will be created in the room and air flow through the exhaust system will be reduced. Dilution Ventilation General Exhaust Ventilation A form of exposure control that involves providing enough air in the workplace to dilute the concentration of airborne contaminants to acceptable levels. For example, a stack placed 30 ft away from an air intake should be at least 10 ft higher than the center of the intake. Troubleshooting an Exhaust System--Some Helpful Hints Most of the following checks can be made by visual observation and do not require extensive measurements.
The amount of reentrainment depends on exhaust volume, wind speed and direction, temperature, location of intakes and exhausts, etc. Introduction Industrial ventilation generally involves the use of supply and exhaust ventilation to control emissions, exposures, and chemical hazards in the workplace. They are easy to read and portable but require regular calibration and maintenance. Time the smoke plume's travel over a two-foot distance. For problems with accessibility in using figures and illustrations in this document, please contact the Office of Science and Technology Assessment at 202 693-2095. Pitot Tube A device used to measure total and static pressures in an airstream.