If the tapping produces heavy, thudding sounds and no sheet metal vibration, liquids or settled dust may be in the duct.
Will the project meet OSHA requirements if it is built as proposed? Establish a preventive maintenance program. Prevention and Control A well-designed system and a continuing preventive maintenance program are key elements in the prevention and control of ventilation system problems.
Drawings are usually drawn to scale. The degree of hazard is related to toxicity, dose rate, and individual susceptibility ; Emission sources are primarily vapors or gases, or small, respirable-size aerosols those not likely to settle ; Emissions occur uniformly.
Time the smoke plume's travel over a two-foot distance. Equipment Operability Before taking velocity or pressure measurements, note and record the operating status of the equipment. Use steam for humidifying. The minimum velocity that can be read by an anemometer is 50 feet per minute fpm.
Do plans and specifications adhere to slot hood face velocity codes, standards, requirements,policies, and do they recommend good practice as established by the industry? Mark ambiguous phrases, "legalese," and repetition.
Check dimensions and lengths with a ruler or a scale to be sure that this is the case. Plant and Process Ventilation. Tobacco Smoke in Air OSHA has published a proposed rule for IAQ including tobacco smoke in the workplaceand this rulemaking is likely to be completed in the near future.
Avoid use of water sprays in HVAC systems. Documentation The characteristics of the ventilation system that must be documented during an investigation include equipment operability, physical measurements of the system, and use practices. Anemometers often cannot be used if the duct contains dust or mist because air must actually pass through the instrument for it to work.
For example, they need to know how to work safely and how best to utilize the ventilation system.
Maintain written documentation not only of original installations but also of all modifications as well as problems and their resolution. Combinations of controls are often employed for HVAC purposes. Measurements can be made with measuring tape.
For example, are filters loaded or clean? This table is best viewed on tablets, notebooks, and desktop computer screens. Look for conciseness and precision. Volatile Organic or Reactive Chemicals If an organic or reactive chemical e. Hot-wire anemometers should not be used in airstreams containing aerosols.
If the tapping produces a "clean" sheet metal sound, the duct is clear.
American Conference of Governmental Industrial Hygienists. What is to be slot hood face velocity and why? Guidance for Indoor Air Quality Investigations. Slot hood face velocity and discard microbe-damaged furnishings and equipment.
Maximum distance from the emission source should not exceed 1. Duct velocity measurements may be made directly with velometers and anemometers or indirectly with manometers and pitot tubes using duct velocity pressure. An isometric drawing is one that illustrates the system in three dimensions.
Industrial Ventilation, a Manual of Recommended Practice. Measurements Duct diameters are measured to calculate duct areas. Aneroid-type manometers use a calibrated bellows to measure pressures.
Good Practices Hood placement must be close to the emission source to be effective. Workers need to be trained in the purpose and functions of the ventilation system.
They are easy to read and portable but require regular calibration and maintenance. The drawings come in several views: Emission sources contain materials of relatively low hazard.
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. Visual inspection of hoods, ductwork, access and clean-out doors, blast gate positions, hood static pressure, pressure drop across air cleaner, and verbal contact with users.
Inside duct diameter is the most important measurement, but an outside measurement is often sufficient for a sheet slot hood face velocity duct.
Dedicated smoking areas should be configured so that migration of smoke into nonsmoking areas will not occur. Salt Lake City, UT: Air Movement and Control Association. Inclined manometers offer greater accuracy and greater sensitivity at low pressures than U-tube manometers.
Dealing With Micro-Organisms If you suspect microbial agents, check for stagnant water in the ventilation system. Exhaust hoods do little good if the welder does not know that the hood must be positioned close to the work.
Air cleaner and fan condition measurements can be made with a pitot tube and manometer. Hood static pressures SPH should be measured about duct diameters downstream in a straight section of slot hood face velocity hood take-off duct.
Do the specifications spell out exactly what is wanted? Air cleaner capacity, fan housing, pulley belts. The presence of mold or slime is a possible sign of trouble. Are system blueprints available? 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. Nothing convinces management and employees more quickly that the ventilation is not functioning properly than to show smoke drifting away from the hood, escaping the hood, or traveling into the worker's breathing zone.
The measurement can be made with a pitot tube or by a static pressure tap into the duct sheet metal see Figure III: Similarly, the minimum capture velocity should not be less than 50 fpm.
For example, if it takes two seconds for the smoke to travel two feet, the velocity is 60 fpm. Certain elements of any ventilation system should be checked on a regular schedule and replaced if found slot hood face velocity be defective.
The meter should always be read in the upright position, and only the tubing supplied with the equipment should be used. Measurements are made in the center of concentric circles of equal area. Plan sections include electrical, plumbing, structural, or mechanical drawings UCI, Section Selection Criteria for General and Local Exhaust Systems General exhaust ventilation dilution ventilation is appropriate when: Understand the scope of the project.
Air flow in industrial ventilation ducts is almost always turbulent, with a small, nonmoving boundary layer at the surface of the duct. Calculate the velocity in feet per minute.
The approximate relationship of capture velocity Vc to duct velocity Vd for a simple plain or narrow flanged hood is illustrated in Figure III: Ventilation and Control of the Work Environment. Hood-face velocities outside the hood or at the hood face can be estimated with velometers, smoke tubes, and swinging-vane anemometers, all of which are portable, reliable, and require no batteries.
American Industrial Hygiene Association. Remove stagnant water and slime from mechanical equipment. Hood-face velocity measurement involves the following steps: Good practices to follow when reviewing plans and specifications are listed in Table III: Because velocity varies with distance from the edge of the duct, a single measurement may not be sufficient.
If the duct diameter D is 6 inches, then the maximum distance of the emission source from the hood should not exceed 9 in.