aafsmall.gif (1978 bytes)Environmental Products Division
Biological, Chemical and Nuclear Hazards
MailShelter" v. Downdraft


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A Comparison Between the American Air Filter MailShelter" and a Typical Downdraft or Backdraft Table for Mailhandling and Mailsorting Applications

MailShelter

Downdraft or Backdraft Table
The MailShelter is a completely new product which has been specifically designed for the protection of mailhandlers using AAF Internationals knowledge and expertise in airflow dynamics and dust particle collection. The MailShelter is intended to reduce the risk of contamination from dangerous and toxic particulate contaminants.

    Downdraft and backdraft tables are existing products which are being newly applied to the mailroom.

    Downdraft and backdraft tables are intended to reduce nuisance dust in light to medium industrial environments. They are not intended for use in applications where the dust may be dangerously toxic or contagious

The user is isolated from the work environment. The work is performed in an isolated glove box environment and the operators hands and arms are protected from contamination

    The user is not isolated from the work environment. Dust particles will collect on the operators person and clothing
The workspace is maintained under negative pressure relative to the surrounding room environment

    The work environment is part of the surrounding room environment
The velocity pressure through the slots in the glove box isolates any contamination within the enclosure while the fan is operating

    As the distance from the table increases the airflow diminishes rapidly and results in reduced dust particle capture efficiency
The effectiveness of the MailShelter is not impacted by the position or movements of the operator

    The turbulence created by the air flowing around the operator and by the movement of the operator can result in low pressure zones that may cause dust particles generated in the mail handling operation to be drawn into the breathing zone of the operator
During operation, the effectiveness of the MailShelter is not impacted by the operation of the ventilation system in the surrounding environment or by the opening or closing of doors

    The operation of the ventilation system in the surrounding environment or the opening or closing of doors can disrupt airflow patterns into the downdraft or backdraft table causing dust to escape into the surrounding environment
If a contamination event occurs the contaminant is confined to the MailShelter

Because the MailShelter is both isolated from the surrounding environment and not connected to the ventilation system a contamination event will not result in contaminant spreading to the rest of the building

    Any contamination that spreads from the downdraft or backdraft table to the surrounding environment may be carried through the ventilation system and contaminate the entire building
The MailShelter is supplied with internal lighting specifically designed to illuminate the workspace

    Most backdraft and downdraft table designs rely on room lighting to illuminate the surface. Shadows cast by the operators body can result in fatigue and inefficiency
Particulate that becomes suspended in the air inside the MailShelter will be drawn into the filter system. Particles that are large enough to overcome the airflow velocity inside the glove box will fall to the work surface where they can be easily decontaminated during routine clean-up

    When using a downdraft table a significant portion of the work surface will be blocked with the mail that is being sorted and handled. The air space immediately above the blocked surface will be "dead air space." There is a high probability that contaminants trapped on the upper side of the materials in this space will not be sucked into the filter system
The MailShelter includes an internal bin for disposal of envelopes and packaging

    Backdraft and downdraft tables do not typically include any method for safe disposal of envelopes and packaging
The MailShelter glove box and glove box access has been sized to accommodate and allow manipulation of a standard USPS mail bin

    The open top of a standard USPS mail bin sits well away from the suction surface of a downdraft or backdraft table. The airflow velocity at this location may not be adequate to capture dust particles that are emitted by movement of the contents of the mailbin. Similarly, dust particles that are emitted by tipping or emptying the contents of the mailbin onto the work surface may also escape into the adjacent environment
The MailShelter offers an adjustable work surface height

    The work surface height on a downdraft or backdraft table is generally fixed
The MailShelter is portable. It is supplied with casters and can be easily moved. It also includes a standard power cord and plug for connection to any standard 15 amp, 120 volt wall outlet

    Downdraft or backdraft tables are generally not portable and may require 230 or 460 volt power supplies