Fume hoods maintenance

Fume hood maintenance involves periodical (daily, quarterly, annual) cleaning, maintenance, calibration, qualification and inspections. In daily inspection the fume hood area is visually inspected by the operator. Hood function indicating devices (LEDs) are a part of the modem fume cupboard. Periodic inspection covers capture or face velocity measured with a velometer or anemometer. 

Exhaust air from primary containment devices (fume hoods, safety cabinets or other) shall be appropriately treated by filtration using a high efficiency particulate air filter (HEPA), or by adsorption, absorption, reaction, incineration, or dilution used individually or in an appropriate combination. If HEPA or charcoal filters are used, these must be installed and operated to permit decontamination, maintenance, and replacement without exposing personnel or causing contamination of the environment. 

Fig. 15.3. Short-barrelled rotary furnace undergoing maintenance. Note, fume hood and ductwork has been removed.

The major hazards associated with the AIMS were feed and product flammability, chemical exposure, and elevated process temperatures. The risk of hre in the system was reduced by the use of diluted feed streams that did not allow the formation of flammable mixtures in the system. In addition, system interlocks prevented the uncontrolled release of process gases in the event of an incident. These interlocks also minimized the risk of exposure of the system operators to process gases. In addition, the process was entirely contained in a fume hood, so following the system Standard Operating Procedures (SOPs) helped prevent such exposure. The risk of injury due to high temperatures in and around the system was also be minimized by closely following the system SOPs during operation and system maintenance. A detailed description of all process hazards is omitted here for brevity. 

One advantage of miniaturization is that the entire system could be easily moved to another location for maintenance. Figure 12.16 compares the AIMS to the flow manifold for a MARS Version VI. An oven that houses the MARS parallel reactor bank was removed from the hood to provide a clearer perspective view. The front area of the AIMS occupied about one-tenth of the area of the MARS flow manifold. Obviously, the AIMS offers a significant advantage by reducing the space requirements in a fume hood. In addition, an operator can easily access all of the parts of the AIMS without needing a footstool or stepping inside the hood. 

It is often possible to reduce air-input requirements- by removing the hazardous material at the point of discharge by loccd ventilation. This lowers the ta value in Eq. (8-5), which assumes possible disposal of hazardous material within the entire enclosed volume of the enclosure being ventilated. Hoods and exhaust ducts are placed over such equipment as open filter presses, pulverizers, open tanks, and over laboratory benches and equipment to catch the maximum amount of vapor or dust without interfering with normal operation and maintenance. Local air velocities in the region of pickup will depend on density of the hazardous material or its particle size if a dust or fume. Air velocities greater than 200 fpm are usually employed for industrial operations, while chemical laboratory fume hoods range from 70 to 125 fpm when fully opened. 

No safety feature or interlock of any equipment in the facility shall be disabled without written approval ofthe laboratory supervisor. Any operations which depend upon the continuing function of a critical piece of safety equipment, such as a fume hood, shall be discontinued should the equipment need to be temporarily removed from service for maintenance. Any such item of equipment out of service shall be clearly indicated with a signed Out of Service tag. Oiily the person originally signing the tag, or a specific, designated alternate, shall be authorized to remove... 

The CHO should conduct, or have done under their supervision, laboratory inspections of equipment, specifically including fume hoods and other fixed safety equipment, maintenance and housekeeping, chmical storage, and compliance with the organization and laboratory-specific safety plans. 

Systems involving toxic gases should be adequately ventilated. If possible, the systems should be set up totally within a fume hood. Large walk-in hoods often are used for this purpose. All systems should be carefiiUy leak-tested prior to introduction of toxic materials into the system, periodically thereafter, and after any maintenance or modifications to the system which could affect its integrity. 

Both methods require minimal if any sample preparation, and extensively automated systems are available. The highly corrosive chemicals and the harsh conditions used in the Kjeldahl digestion call for appropriate fume hoods and exhaust systems, and standardization of the digestion itself may sometimes be difficult. The relatively low sensitivity and the fairly large amount of sample required are usually no problem in the food industry. As for chromatographic methods, controlled oxidative pyrolysis of food releases a number of volatile compounds that may foul the separation columns. This requires careful maintenance of the equipment, and in particular of the precolumn that guards the separation apparatus. 

Acid and solvent fume hoods bulkhead mounted in the BNC cleanroom. Bulkhead mounting equipment allows the separation of the operational side of the equipment (shown) from the maintenance side of the equipment, accessible through the cleanroom chase. 

The auxiliary air chemical fume hood includes an additional blower that injects air into or at the face of the hood, providing additional flow inside the enclosed cabinet. These types of hoods are rarely installed in renovations or new construction, but may be encountered in older laboratories. They are less desirable than the standard/conventional, bypass or variable volume types because they require a great deal of energy to operate (although the early designs featured the addition of an auxiliary air stream that was not air conditioned). These devices are mechanically more complex than other types, and consequently more prone to maintenance problems. 

The motor of the chemical fume hood should be running at all times, except for maintenance. If a switch is located inside the laboratory, it should be equipped with a lockout to protect maintenance staff. 

Fume hoods and other associated protective equipment should be maintained in satisfactory operating condition at all times. Monitoring of performance and any scheduled preventive maintenance should be done in accordance with the manufacturers suggested guidance. The OSHA Laboratory Standard states that fume hoods need to have a hood velocity of 60 to 100 linear feet per minute to be considered as adequate. In order to ensure that lab fume hoods continue to meet this standard, the Safety Division performs quarterly fume hood inspections. Moreover, during each inspection fume hood velocity checked. For each hood inspected an individual inspection sheet is used and all entries resulting from the inspection must be made there. 

According to the ambiguous instructions written in the log for the operator, he should have pressured up the ammonia condenser to compressed air system pressure. Next, ho should block off the air supply and discharge ammonia fumes into the atmosphere. The operator pressurized the ammonia-laden condenser to full air system pressure, but unfortunately did not block it off. Therefore at the beginning of the day when the arriving maintenance mechanics and operators put a high demand on the air system, the condenser acted as a surge tank. As the system pressure dropped, undesirable ammonia fumes traveled to the sandblaster s hood. 

It is recommended that if it is desired to manifold more than one hood into a common duct, prior to the entry into a common plenum at negative pressure to the individual ducts, that this practice be limited to hoods within the same room. Otherwise, it is less hkely that individuals using different hoods would be aware of each other s activities, and one might make changes which would affect the performance of hoods in the other room.. For example, a pressure dififerential might be established between one laboratory and another, so that fumes could be exchanged between the two areas. In addition, maintenance of the air balance in the individual rooms may be made more difficult, and there may be problems in complying with fire codes, if fire walls are penetrated. 

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