Negative Pressure Rooms (NPR's)

Typical postal room installation in bank postal processing centerNegative Pressure Rooms are low cost, leak-tight rooms used to house dangerous human-intensive inspection processes. Many of these rooms are currently being used for front-end postal operations in governmental departments and large high-profile private businesses. Other application areas include customs inspection; border crossings; and the handling, processing and packaging of known toxic materials.

Incoming postal articles can be a weak link in private or public infrastructure. If hazardous substances are allowed entry through the postal system, key personnel may be injured and day-to-day operations severely hampered. Losses may accrue at the rate of millions of dollars per day or more, and buildings may become unusable. Research International and its partner, American Safe Air, provide both standard and custom examination rooms and monitoring equipment to prevent such incidents from happening.

These rooms provide a controlled environment for inspection operations and generally include one or more D1000 downdraft table and various CBRNE monitoring devices such as the ASAP II or ASAP V, depending on the customer’s threat profile. In this way many types of dangerous substances that may come in with postal or other items are identified and contained before being released into a governmental or business work area where many lives might be lost and/or costly infrastructure damaged.

These rooms are typically constructed of light-weight aluminum extrusions and transparent high-strength polycarbonate plastic (Figure 1). Use of a transparent wall material minimizes claustrophobia of workers inside the room, and allows visual surveillance of room operations from outside the room. The rooms operate slightly below ambient atmospheric pressure. Incoming and exhaust air for the rooms are both filtered through high-efficiency HEPA filters and access is often through air lock-style doors, making the environment within the rooms similar to that in an electronic or pharmaceutical clean room. Workers with allergies find that working in the rooms greatly relieves breathing problems.

These rooms provide a controlled environment for postal operations and generally include one or more D1000 downdraft table and various CBRNE monitoring devices such as the ASAP II or ASAP V, depending on the customer’s threat profile. In this way many types of dangerous substances that may come in with postal items are identified and contained before being released into a governmental or business work area where many lives might be lost and/or costly infrastructure damaged.

Figure 2. Downdraft air flow strategy  used in the Negative Pressure Postal Rooms

The NPR's environmental control system utilizes proven HEPA filtration technology for particulate control and carbon/zeolite filtration technology for chemical gas control. The HEPA filters employed have an efficiency of 99.97% or better for any particle greater than 0.3 microns in size. By way of comparison, a single anthrax spore is from 1.0 to 1.5 microns in diameter.

Ambient air or filtered, cooled and recycled NPR air is injected into the room from roof-mounted fixtures, creating downdraft conditions within the room. Depending on the size of the NPR, it is fitted with a number of these filtered downdraft air injection vents. Air handlers with HEPA discharge filters are used to remove air from the room. A typical system completely changes the air once every minute. In comparison, United States OSHA standards for smoking lounges require only 60 CFM per person- a rate nearly ten times less than an NPR (see Figure 2).

It is generally possible to couple the exterior air handlers discharging air from the NPR with the D1000 downdraft tables so that each exhaust filter ensemble contains a foam large-debris prefilter, two HEPA elements in series, and an activated carbon/zeolite filter as in Figure 3.

Filtration Arrows in Negative Pressure Room

As discussed, the NPR’s conditioned air system provides a flood of clean air from the ceiling while removing potentially contaminated air by evacuating it through blower-powered air handlers. Air is filtered as it enters the room from the ceiling and then filtered twice more as it leaves the room. The system is deliberately redundant to provide maximum safety to employees both in the room and outside the room. Filtered air discharged from the room is so clean that it has been reported by representatives at a major oil company that since installing and using their NPPR, the company has found a significant reduction in particulate count for the entire floor of their Houston, Texas headquarters.

For further information on a negative pressure room for your application, contact us at info@resrchintl.com or 1-800-927-7831.

 
 
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