Makeup Air

Makeup air shall be provided to replenish air exhausted by the ventilation system. Makeup air intakes shall be located so as to avoid recirculation of contaminated air within enclosures (UMC 505.6). As a practical matter, the amount of makeup air required to replace the exhaust air sca pressurizeihQ cleanroom space may be significantly higher than the exhaust flow (t5q)ically 10% to 25% more than the exhaust flow rate, depending on the integrity of the construction). 

Emergency power is required to operate the exhaust ventilation and treatment systems in H-6 occupancies and H-2, H-3 or H-7 facilities where toxic or highly toxic gas is used. Emergency power must be on-line within ten seconds offailure of the primary power source. 

We believe that cleanroom pressurization should be maintained to control cleanliness. Therefore, it is recommended that each facility consider providing emergency power for outside makeup air handlers with capacity in excess of exhaust air quantities. Failure to do so could result in a cleanroom going negative with subsequent inadvertent contamination. 

It is prudent, if not mandatory, to provide emergency power, or preferably an uninterruptible power supply (UPS) for all controls which operate the life safety-related equipment and ventilation systems. 

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The unbalanced local exhausts take their makeup air through the building openings ... 

Heating makeup air to take care of the ventilation loss... 

To determine the heat requirements of makeup air, the following equations can be used. 

Depending on the application, the air-change rate may range from 0.5 to 100 air changes per hour. It must be remembered, however, that adequate provision must be made for the makeup air to enter the space without creating discomfort or other problems. 

Drafts from windows and doors can have speeds that exceed that through the face of the enclosure. This can be especially so where the makeup air does not balance the amount extracted by the endosure(s). Doors should be kept closed unless the room has been specifically designed to operate otherwise. 

A fume cupboard should not be positioned where the only escape route from the area would necessitate passing directly in front of the fume cupboard. Siting with respect to makeup air grills should be considered carefully (see above on drafts and cross-flows) and a minimum separation distance of 1500 mm is recommended. ... 

In all cases, it is necessary to supply adequate makeup air while still maintaining appropriate pressure differences. A study of five hospitals in... 

Chicago showed that lack of mechanical makeup air resulted in contaminated air reentering the hospital, and therefore these rooms were not isolated from adjacent spaces. 

Each hood intended for toxic work must have a face velocity of 100 linear feet per minute. When many hoods are employed, the volume of tempered air that must be supplied (summer and winter) is quite large. The required airhandling equipment is so massive that minor misadjustments may make it difficult to get out of a room because of air pressure on a door. One way to deal with this is to vent the doors and keep the hallways at a slightly higher pressure than the labs. When an airhandling (supply) unit falls short, the hallway provides needed makeup air. Computers can operate air handling systems more precisely than can traditional systems and an alarm system that pinpoints defective elements for early repair can help avoid gross imbalances. 

Safe havens may be rare on some sites however, many buildings can provide personnel with temporary protection until the incident has been analyzed and a decision made on the need for evacuation. To qualify as a designated temporary safe haven, a building must be reasonably well sealed against air infiltration, with adjustable ventilation systems that can reduce or close off exhaust vents and outside makeup air. Emergency procedures should state how long a building can be considered a safe haven under specified exposure conditions. 

Adequate makeup air to prevent indoor air-quality problems... 

Room temperature control and adequate venhlation are the most critical factors in designing the panel room. In order to maintain a comfortable temperature in the room, air-conditioning should be installed. A slight positive air pressure should be maintained in the booth area to prevent inhltration of external odors. Individual exhaust ventilation ducts should be located in each booth. Air turnover in the room should occur at least every 30 seconds (1). Recirculated and makeup air should pass through activated carbon filters to remove odors. 

Flue gas is supplied to the scrubbing system with a forced draft fan. Typically, the fan is designed for 20 inches of water pressure drop and is equipped with the typical draft control mechanism. A secondary damper is connected to the vacuum side of the fan. The secondary damper admits makeup air and thereby automatically maintains optimum gas flow in the scrubber during varying loads in the boiler operation. 

Low levels of an applied herbicide/pesticide mix were drawn into the air conditioning makeup air of a commercial building. Workers reported neurological symptoms that included nausea, dizziness, and headache immediately after the pesticide mix was applied. Chemicals contained in the mix included... 

It is now generally accepted that combustion is the almost exclusive source of the carcinogen and endocrine-disrupting chemical family of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/F or dioxins for short). Dioxins are part of a broader class of chlorinated organic air pollutants that are produced by most combustion sources. All that is necessary are a small source of chlorine (that may even be in the combustion makeup air), a catalytic metal, and a hydrocarbon. 

Various control schemes have been used in conveyor dryer systems. When a steam heater is used to heat up the makeup air, the temperature of the circulating air through the dryer is controlled by adjusting the steam-control valve [40]. 

It must be possible to open a door coming from the normal direction of egress without using a key. Draw bolts, hooks, bars, or similar devices cannot be used. An essential element of a door is that it cannot be too difficult to open. The opening force for most interior doors must not exceed a force of 5 pounds. To open a door that is normally power assisted must not require more than 50 pounds with the power off. Panic hardware must require no more than 15 pounds force to release, and a door not normally provided with power assistance cannot require more than 30 pounds force to initiate motion and swing to a full-open position with apphcation of a 15-pound force. These restrictions on the force required to operate a door can easily be exceeded should the ventilation system be modified without taking this concern into account. A very moderate atmospheric pressure differential of just over 0.3 inches (water gauge) would result in a force of more than 30 pounds force on a door of the minimum acceptable size. Addition of hoods to a laboratory, without provision of additional makeup air, could easily cause this limit to be exceeded on a more representative 3 foot by 7 foot door. 

Another possible problem in working with materials which are toxic is failure of the system and releasing toxic vapors into the facility. In one case, such a failure occurred in a system set up properly in a fume hood. Unfortunately, the exhaust of the fume hood was too close to a nearby open window, and a student working near the window was overcome by fumes drawn into the window. A major contributor to this incident was an overtaxed ventilation system with insufficient makeup air so that the building as a whole was at negative pressure. 

The makeup-air unit supplying Zone 2 receives its air from the building distribution system, the Zone 3 ventilation system (fan 3), boosted by fan 13 and recirculated by fan 11. The volume of makeup air is determined by the amount of air exhausted from the east and west Zone 2 sections, the amount of makeup air supplied to Zone 2A (which includes the Zone 1 supply air), less the amount of infiltration air into Zone 2. In addition to maintaining the correct pressure differential, the Zone 2 system provides at least four air changes per hour in Zone 2 and provides necessary environmental conditioning. The volume of recirculated air is regulated by a manual intake damper located in the intake duct of the Zone 2 filter and cooling coil. 

An injury where there is loss of time to the injured person and a medical expense. Makeup Air... 

Each operation shall be provided with continuous local exhaust ventilation so that air movement is always from ordinary work areas to the operation. Exhaust air shall not be discharged to regulated areas, non-regulated areas, or the external environment unless decontaminated. Clean makeup air shall be introduced in sufficient volume to maintain the correct operation of the local exhaust system. 

Except for outdoor systems, regulated areas shall be maintained under negative pressure with respect to nonregulated areas. Local exhaust ventilation may be used to satisfy this requirement. Clean makeup air in equal volume shall replace the air removed. 

The maximum rate of gas suppiy to the make-up air heater burners must not exceed that which wouid yieid in excess of 200 p.p.m. (parts per miiiion) of carbon monoxide or 2,000 p.p.m. of totai combustibie gases in the mixture if the unburned gas upon the occurrence of fiame faiiure were mixed with aii of the makeup air suppiied. 

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