Protecting Against Airborne Chemicals

Several months after Sept. 11, the chief engineer of a 40-story office building realized he had a problem. The building had been designed with the outside air supply on the ground floor at street level in front of the building. All it would take was a canister of poisonous gas to be opened on the sidewalk and thousands of his tenant’s key personnel could be dead or dying within minutes.

The engineer and his building’s owners believed they had three choices:

• Spend several million dollars to reroute the buildings fresh air supply;

• Spend hundreds of thousands of dollars upgrading their HVAC and filtration system to handle HEPA and Gas Phase Filtration and add $20,000 to $30,000 to the annual filter budget; or

• Do nothing and pray nothing happens.

However, upgrading a building’s defenses against the plague of modern terrorism does not need to be an all-or-nothing proposition. Here are some ideas to consider when upgrading a facility’s survivability.

• Survey the outside air supply. Where is the outside air supply located? If it’s on the ground floor can it be moved or secured?

• Beef up the facility’s outside air handler’s filter system. Experts say that positive air pressure or over-pressured filtered air is the best way to protect from infiltration of poisonous agents. The Israelis, the U.S. military and the Centers for Disease Control (CDC) use over-pressure to protect buildings and vehicles from biological, nuclear and chemical agents. There are now mini-pleated all-plastic filters (that can be gasketed) with minimum efficiency reporting value (MERV) ratings as high as MERV 15 with excellent pressure drops in 1-, 2- or 4-inch panels and 12-inch V-Cells. Filter life cycle and costs analysis show these filters can reduce overall filtration costs over less efficient filters. A set of gas phase filters also could be kept on hand, just in case.

• Take a look at air flow in the facility. If a chemical or biological agent were released in the lobby, would it spread throughout the entire building? Maybe there are some air handlers that are key to limiting the spread of agents that could be shut off in the event of an incident, or filtration could be upgraded in these air handlers.

• Get serious about air filter bypass. This may be the cheapest protection to add to a facility. If one is using MERV 8 pleated air filters, which will filter around 70 percent of particles in the 3-10 micron range and can place the width of a business card between the frames, there is a 100+ micron gap. Users should look for evidence of bypass dust trails on the air handler’s doors, behind gaps in filter frames and of a buildup of mold and dust on coils behind areas where bypass occurs. All filters should be gasketed or taped to all the air that passes through the filter bank. All spacers should be air tight, if not they should be replaced. Poly foam spacers that fit tight against the door are inexpensive and can be thrown away when they lose their spring. All the cracks should be sealed; all the gaps plugged, and no unfiltered air should pass.

• Get help. There are a number of good Web sites for information. A place to start for specific information is the CDC Web site Guidance for Protecting Build Environments from Airborne Chemical, Biological or Radiological Attacks at www.cdc.gov/niosh/docs/2003-136/2003-136d.html. The National Air Filtration Association’s Web site at www.nafahq.org also has good information and listings for a number of excellent contacts for Indoor Air Quality.

• Be creative. Dreaming up creative ways to protect a facility is better that waking up to a nightmare.

Dean Philpot works with Filtera.com as a certified air filtration specialist (National Air Filtration Association). He has worked extensively with facilities complying with the LEED Standards (green building) and facilities seeking gas phase filtration.