This web site is intended for emergency personnel and for building operators. It contains our current
advice for dealing with a biological or chemical release in a building. It will be updated as our
The advice on this site is appropriate for small and medium-sized releases such as those that
would be expected from a terrorist attack, not for industrial-scale releases
such as those at Bhopal, India or Chernobyl, Ukraine.
This web site was prepared by the Airflow and Pollutant Transport Group at Lawrence Berkeley National Laboratory. We have substantial knowledge and experience (1.03MB PDF document, 2 pages) in protecting buildings and occupants from chemical or biological attack. Click on the title bar, above, for more information on our group, department, or laboratory.
Immediate Actions to Safeguard a Building Against a Chemical or Biological Attack
- Identify fresh air intakes and prevent unauthorized access.
A terrorist can quickly contaminate a building with a chemical or biological agent by introducing it into the building's ventilation system. This can be done even without access to the interior of the building through the building's air intakes.
Some buildings have air intakes that are inaccessible (e.g. on the roof), but others have intakes that are vulnerable.
Even keeping the public a short distance away from the air intake may not provide complete security. For instance, a plastic bag containing anthrax spores could be tossed into an air intake from some distance away.
Baffles over the air intake can make this type of attack less likely to succeed, but they might also affect the amount of outside air the building
can pull in, and the energy efficiency with which this can be done, so they should not be installed without careful evaluation.
Contrary to the expectations of building designers and operators, many buildings take in large amounts of air through the building exhausts;
this phenomenon occurs during warm weather, in buildings that don't have a return fan or that use volume-matching to control the return fan.
Since building designers assume there will be no inward flow through the exhausts, exhaust registers are often placed on loading docks or
adjacent to sidewalks, so they may be particularly vulnerable. Determine whether your building is subject to this phenomenon; if it is,
consider restricting access to the exhausts, or modifying the return fan controls. Ensuring that there is never significant inward flow
through the exhaust registers will prevent introduction of chemical or biological agents through this route.
- Secure mechanical (HVAC) room doors to prevent unauthorized access
A terrorist with access to a building's HVAC (heating, ventilation, and air conditioning) equipment can quickly contaminate
the entire building, or at least the entire ventilation zone, with a chemical or biological agent. The rooms that contain HVAC
equipment should be locked, and keyed so that they can be opened only by staff who need access.
- Secure building plans and HVAC plans from unauthorized access.
A terrorist who wants to maximize the casualties from an indoor chem/bio attack, or to target specific people, can use knowledge
of the building's ventilation system: how many ventilation zones does the building have, which air vents serve which rooms, etc.
The easiest way to determine these facts is from the building plans.
Building plans and ventilation system details should be available only to people who need them. If they are provided to contractors for
building work, they should be recovered after use if possible. Building managers and maintenance personnel should be wary of requests
for information about ventilation system details.
- Develop an emergency response team and establish operational details.
Any emergency requires rapid response in a number of areas: evacuation assistance, communication with authorities, etc.
A team of people with well-defined responsibilities should be created, with backups when the selected people are not available.
Among the responsibilities are: (1) main decision-making: should the building be evacuated, should the HVAC system be turned off, etc.;
(2) contacting authorities (fire department, police, etc.), (3) providing instructions to building occupants, (4) manipulating the
HVAC system as needed, (5) coordinating first aid.
- Plan and practice separate emergency response procedures for indoor and outdoor releases of chem/bio agents.
The first response to an outdoor chem/bio release should include shutting down the building's ventilation system and
closing all doors and windows. In contrast, the response to an indoor chem/bio release should include evacuation.
Building operators should understand the differences in the best responses to
indoor versus outdoor releases, and should practice the steps they will take in each case.
Long-Term Actions to Safeguard a Building Against a Chemical or Biological Attack
This is a list of some of the actions that can help make a building safer in the event of a chemical or biological release. Which of these should be performed for a particular building, if any, depends on the costs and the level of threat.
- Ensure that building operators can quickly manipulate the HVAC control systems to respond to different kinds of attack.
It should be possible to immediately shut off the HVAC system (including closing dampers that admit outdoor air and closing
exhaust dampers), or to put the system on 100% fresh (outdoor) air. Dampers should be checked for leakage, and replaced or repaired
Areas served by different air handling units should be surveyed and clearly shown on floor plans so that building operators know
which supply and exhaust systems serve which areas. Maintain an updated copy of the ventilation plans in the room(s) from which the
HVAC system can be controlled.
There should be at least one secure location (preferably more) from which the whole HVAC system can controlled, so it is not
necessary to move through a contaminated building to manipulate the system.
- Upgrade HVAC particle filters and seal gaps to prevent air bypass.
Most building HVAC systems have some type of particle filter. Substitution of a more effective filter (particularly for
small particle sizes) can reduce the risk of spreading a biological agent through the building via the HVAC system.
However, more effective filters can lead to a significant pressure drop, which can pull unfiltered air around the
filter or through leaks in ducts between the filter and the fan. To minimize or eliminate increases in pressure drop, deep
pleated filters or filter banks with larger inlet area can be used if space allows.
Improved filters can provide significant protection from a biological release,
but they should be installed correctly and ducts should be sealed to reduce air bypass.
Installing new filters may require changes in other equipment too, in order to maintain air quality and
comfort, and may increase energy use, so it should not be done without careful evaluation.
- Establish internal "safe zones" for sheltering-in-place, and exterior locations for evacuation.
For an outdoor release, people should remain indoors.
"Shelter-in-place" rooms can be created or identified, where people can stay in the event of an outdoor release. The goal is to create areas where outdoor air infiltration is very low. Usually such rooms will be in the inner part of the building (no windows to the outside). They should have doors that are fairly effective at preventing airflow from the hallways (e.g. they should have no gap or only a very small gap at the bottom of the door). Bathrooms are usually a bad choice, because they often have an exhaust duct that leads directly to the outside. If the exhaust fan is left on then air will be drawn into the bathroom from other parts of the building, which will become contaminated. If the exhaust fan is turned off, then the duct can allow outside air to directly enter the bathroom. Exhaust fans for bathrooms and utility rooms are often controlled separately from the HVAC system.
Opening and closing a conventional door can pump large amounts of air into the room; replacing the door with a sliding door, if practical, can reduce this effect.
Additionally, it may be possible to provide purified air to the safe area, depending on whether the pollutant can be removed by the building's air filtration system. Modifications to the HVAC system can add filters and an air supply that are dedicated to
the safe area.
For an indoor release, people should exit the building.
The chem/bio agent will be carried out of the building through windows, doors, and vents, so people should congregate upwind of the building.
At least two different evacuation zones should be identified in advance, and the appropriate one should be used depending on the wind direction.
- Do not mix air from mail rooms and other high-risk locations into the rest of the building.
to view an animation of how the ventilation system spreads contamination.
Mailrooms, delivery areas such as loading docks, and areas with public access are the most likely
locations for introducing toxic substances to a building.
If the HVAC systems for these areas do not mix air into the rest of the building,
the spread of the agent will be greatly reduced.
Mixing into the general building air can be prevented either by providing a separate air-handling unit for these areas, or by eliminating return air
for these areas and exhausting them directly. (Contamination may still spread along hallways, etc., but this will be much slower).
Consider adjusting the HVAC supply and exhaust so that the high-risk areas are slightly de-pressurized
with respect to the rest of the building, so that air will flow from other areas into the high-risk
areas rather than the other way around.
- Weatherize the Building to Reduce Outdoor Air Penetration
Cracks around windows and doors allow conditioned air to escape the building, and outdoor air to enter. Sealing these gaps can reduce the amount
of flow between the building and the outside, thus improving energy efficiency and slowing the rate at which contamination enters the building
from the outdoors.
Many large buildings have a small surface-to-volume ratio. In such buildings, weatherization is unlikely to have a large effect on reducing casualties
from an outdoor chem/bio release. On the other hand, this improvement might pay for itself in a few years, and improve occupant comfort (especially in
the offices on the perimeter of the building), in addition to potentially improving safety for a chem/bio attack, so this action is worth considering.
Chemical or Biological Attack, Indoor Release
Distinguishing between a biological release and a chemical release:
A biological agent will almost never cause immediate symptoms; a chemical agent almost always will. For a biological agent
the goals are to reduce the total number of people exposed and to be sure you can find everyone who was exposed. For a
chemical release, the goal is to minimize the concentrations to which people are exposed.
For any indoor release, whether chemical or biological: if evacuation can be done safely, evacuate the building to a meeting
point upwind of the building.
Biological release (or unknown):
Shut off HVAC and close outdoor air dampers (or, if this is not possible, put them into full recirculation mode).
Local exhausts, such as those serving bathrooms and kitchens, must also be shut offthey are often controlled
separately from the HVAC system.
These actions will prevent the building from becoming a source of contamination
for people outside.
If possible, stairwells should be pressurized with 100% outdoor air to provide an evacuation route. Other HVAC, and
bathroom and utility room fans, should be shut off.
Segregate people known to be exposed, to avoid contaminating others via contact with clothes or skin, and tag or
mark these people for medical treatment and decontamination.
For a biological release, the goal is to minimize the total number of people exposed, even if this leads to higher
or longer exposure for some people.
It is best to leave the HVAC system operating without alteration, unless a knowledgable building operator is available to perform HVAC manipulation.
Under normal operation, the HVAC system will provide some outdoor air and will exhaust some indoor air, so it will help
dilute the chemical and exhaust it from the building.
Also, for most buildings the normal operation of the HVAC will tend to isolate areas that are served by different air handling units,
thus helping to slow the spread of contamination. The isolation is reduced if the HVAC system is not properly
balanced, or if the building's air recirculation system mixes air from different supply zones.
If the building operator has checked system operation and is sure that dampers and fans are working correctly, some
HVAC manipulations can be beneficial. The simplest such action is to put the building on 100% outside air (no recirculation), with supply and
exhaust fans on full power.
If more sophisticated actions are possible, then do the following:
- The operator should be aware of the possibility of a release into the building air intakes, and should shut
off the supply from any intake in which this is thought to have occurred.
- Pressurize stairwells with 100% outdoor airthis will help provide a safe evacuation route.
- Put the air handlers that serve heavily contaminated areas onto full exhaust and shut off supply to those
areasthis will force air to flow from safe areas to contaminated areas, rather than the other way around.
- Provide 100% outdoor air to uncontaminated areas and areas with people in themthis will help keep people
safe, as long as the chemical isn't being released into those areas' air intakes.
- Depending on the HVAC design, some of the items above may be performed by putting the building into a "smoke removal" mode.
Chemical or Biological Attack, Outdoor Release
For a release into a building air intake, shut off the supply from that intake, but otherwise
follow the advice for an indoor release; in particular, evacuate the building.
For an open-air outdoor release, do the following:
Shut off HVAC fans.
Close fresh air intake dampers.
Close exhaust dampers: with the HVAC off, they can act as intakes.
Turn off exhaust fans in bathrooms, utility rooms, kitchens, etc.; these are commonly controlled
separately from the HVAC system.
Close windows and doors.
People should stay indoors, unless authorities give an evacuation order.
People should retreat to a safe zone in the interior of
Chemical or Biological Attack, Unknown Release Location
It is imperative to determine whether the release is indoors or outdoors.
It would take a very large or very toxic outdoor release to cause severe effects on people indoors. If this
has occurred, there will probably be obvious signs: birds falling out of trees, people collapsing on
the street, etc. Also, an outdoor release will usually affect people throughout the building (because
all ventilation zones constantly get some outdoor air), whereas an indoor release will often affect some
areas of the building much more quickly and more severely than others.
If there are no visible signs of an outdoor release, and if some areas of the building appear to be more severely affected than
others, then assume the release is indoors.
A release into one or more of the building's air intakes is also possible. Shutting off the air supply for any area that
is known to be contaminated, and putting that area on full exhaust, is good advice whether the release is in the air intake
Animation Showing How HVAC Spreads Contamination
This animation shows how the HVAC system spreads contamination through
part of a building. The animation runs at faster than real-time, and
shows the spread of gas after a very rapid release of gas (not from a
continuous source). The times shown are for the building that is being
illustrated the rate of spread and exhaust depend on the details of
the building the ventilation system.
The exhaust damper and mixing box (air intake) at the top of the
building are schematic; the actual devices may look different, and may
be positioned elsewhere on a building.
First Responders Information
Training materials include:
Simple information about building ventilation, for emergency responders.
Print version, 2.0 MB PDF
Screen version, 165.6 KB PDF
Summary of advice on what actions to take during a chem/bio release, for building operators or emergency responders.
Print version, 962.8 KB PDF
Screen version, 81.2 KB PDF
A presentation about using building-specific information to protect a building against chem/bio attack.
Presentation, 2.3 MB PDF
A presentation on assessing vulnerability of buildings.
Presentation, 991KB PDF
A detailed report discusses all of our advice on this website, and gives the assumptions and reasoning behind each item. It is posted below. This report also includes the four-page "advice for first responders" document and the two-page "actions to take" document, in an appendix. The report presents our thinking at the time of writing (July 2002).
Report, 3.11MB PDF
Brochure, 1.03MB PDF
A pdf reader is needed in order to print these files. If you don't have Adobe Acrobat, get it here.
Web Sites with Related Information
Buildings and Building Operation
- The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE), is a good source of information about buildings and building technology. They have issued a statement with guidance on keeping buildings safe from chem/bio-terrorism and other "extraordinary incidents." Some of this advice differs from ours, but the document is still an excellent source of information.
- The U.S. Army Edgewood Chemical Biological Center and the Army Corps of Engineers Protective Design Center [ http://buildingprotection.sbccom.army.mil/basic/airborne_hazards_report_download.htm] have produced a document on how to prepare for a chem-bio attack. The report emphasizes pre-event planning, but also gives advice on action to take during an event. Some of this advice differs from ours, but the document is still an excellent source of information.
- The National Institute for Occupational Safety and Health (NIOSH), part of the Centers for Disease Control (CDC), has issued guidance for protecting buildings from an airborne chemical, biological, or radiological attack .
- Protecting Building Occupants from Biological Threats: Website from the Center for Biosecurity of UPMC that includes useful information about biological threats to building occupants, practical steps for reducing risk, and costs and benefits of risk reduction measures, along with a wealth of related materials and additional resources.
- The National Academies of Science [ http://search.nap.edu/firstresponders/ ] has a comprehensive set of links to sites that give advice for "first responders" (police and firefighters).
- The U.S. Army Edgewood Chemical Biological Center and the Army Corps of The US Department of Justice (DoJ) Office of Domestic Preparedness offers training and technical assistance to state and local jurisdictions to help them respond to, and mitigate the consequences of, incidents of domestic terrorism. The Department of Justice also funds the LSU Academy of Counter-Terrorist Education (ACE) to plan and administer assistance in training emergency response personnel. The DoJ is also funding Sandia National Laboratories (SNL) to establish a Center for Civil Force Protection (CCFP). The Center will provide physical security counterterrorism assistance to state and local law enforcement agencies, other organizations within State and local governments and private industry.
- The U.S. Department of Energy provides information on disaster preparedness, emergency response, etc., at the Energy and National Security web site.
- When a hazardous material is released into the atmosphere, the Atmospheric Release Advisory Capability (ARAC) can map the probable spread of contamination; the National Atmospheric Release Advisory Center (NARAC) provides information at their web site.
- The National Institute for Occupational Safety and Health (NIOSH), part of the Centers for Disease Control (CDC), has a collection of useful information and links related to emergency response to a chemical or biological attack. The Center for Infectious Disease Research and Policy (CIDRAP) at the University of Minnesota, provides a wealth of bioterrorism information, including descriptions of likely agents and their characteristics, and is updated daily.
- The California Peace Officer Standards and Training Commission teaches courses for police officers, including courses on handling a chemical or biological attack.
- interFIRE.org is a complete resource for fire services, fire insurers, law enforcement and others whose duties involve fire investigation.
- A new supplement to the Federal Emergency Management Agency's (FEMA) Guide for All-Hazard Emergency Operations Planning: State and Local Guide has been produced to help state and local emergency planners develop and maintain terrorism annexes to their emergency plans. FEMA also has some information at their Hazardous Materials Guide for First Responders web site.
This work was supported by the Office of Nonproliferation Research and Engineering, Chemical and Biological National Security Program (CBNP), of the
National Nuclear Security Administration (NNSA) under
U.S. Department of Energy
Contract No. DE-AC03-76SF00098.
More information on DOE-sponsored security research can be found at http://www.energy.gov/security.
Additional research that contributed to the web site was performed at the
University of California, Berkeley,
Department of Civil and Environmental Engineering.