WCommercial buildings have existing dampers that can easily be re-

configured to assist in mitigating the affects of a chemical, biologi-

cal, or radiological (CBR) attack.

When analyzing security proceduresfor an airborne chemical, biologi-cal, or radiological (CBR) attack,there are many tactics an engineer

can incorporate into a building’s existing dampersystem to help protect building occupants.

The simpler a system, the better an operatorwho is not an expert at it can understand, main-tain, test, and use it to the best of its capabilities.Commissioning, documentation, maintenancemanuals, instructions, and training are critical.

Almost every building's duct and damperarrangements are unique. In all cases there areprinciples taken from fire and smoke control thatguide any design approach regardless of the type ofsystem. Familiarity with smoke management prac-tices allows the mechanical designer to avoid rein-venting the needed tactics.1

The engineer must individually consider poten-tial attack points – external, air handling intake,

internal, multiple – and consider the options foraction. Before using the damper system, he or shemust thoroughly understand the entire building.Information from sensors and indicator lights,DDC system displays, and manual and automaticalarms must be readily available to operators. Thedesigner must consider all these factors in order tofacilitate the system’s use by staff, fire fighters, orpolice.

STRATEGYThe basic operation of the air handling units

and the fire and smoke system will dictate howthey might be used in an emergency situation.While more could be done in all of the followinginstances, here are some basics:

• Limit transmission of internal release. Isolateany contaminant by isolating the area or floor ofthe building with smoke or isolation dampers.

• Limit injection of externally released agents by

By LARRY FELKER • Belimo Aircontrols (USA) • Sparks, Nev.

CBRU s e o f D a m p e r s f o r

Isolation

2 Homeland Security In Buildings Month Year

shutting down air handlers andclosing economizer dampers inpotentially affected areas.

• Pressurize spaces adjoiningan area where contaminants areknown to be present. This helpsprevent movement from a con-taminated to an uncontami-nated area. The smoke controlzones provide an ideal map;sandwich pressurization systemsprovide a tool. Where smokecontrol systems are not installed,floor isolation is the minimumprudent requirement.

• Exhaust any possible con-taminants outside. Be aware ofdownwind intakes or the possi-bility of spreading to other localareas to avoid exposing other

people. Codes require carefulplacement of exhaust and intakelouvers, but older buildings maynot comply and as of this writ-ing, location of smoke exhaustfan outlets are not covered bycodes.

• Prevent intake of contami-nants if they are externally pres-ent. Shut down all fan systems asa default procedure.

The fire fighters’ control sta-tion should be in a protectedroom with its own air handlerand ideally, separate CBR filtra-tion. Remote modem control bythe DDC system is an option.

The general layouts shown inFigures 1 and 2 show the com-plexity of some situations. Note

that the Figure 2 distributionpretzel is no exaggeration andduct paths are typically hiddenin a structure and/or above ceil-ing tiles. Frequently, drawingsare either absent or inapplicable,making retrofits difficult to de-sign properly. Typically, tradeoffs will be needed to deal withcost versus benefits versus possi-bility of attack.

PRIORITIESThe following goals may be

incorporated into a smoke con-trol and HVAC design:

• Have a written list of priori-ties, action items, and optionsprepared for building operators.

• Sense, alarm, and notify as

Month Year Homeland Security In Buildings 3

necessary. Instructions over thePA system must be loud andclear; panic must be averted.

• Ensure that maintenancepersonnel, BAS or security sys-tem contractors, building secu-rity, police officers, or fire fight-ers can access the control systemsand that they have a copy of thewritten list of priorities.

• Reduce exposure of occu-pants in any area of a buildingwhere toxic agents have been in-troduced.

• Minimize exposure of otheroccupants by stopping spreadthrough building.

• Avoid exposure of emer-gency personnel.

• Avoid spread to other build-ings or outside areas where peo-ple are present.

• Minimize contamination ofthe overall building.

These goals will usually be im-possible to achieve simultane-ously. For example, reducing ex-posure in part of the buildingmay best be accomplished byventilating and exhausting thespace. If the exhaust spreadstoxic agents downwind, theagents may become entrained atthe intake louver of anotherbuilding. This conflict may beunavoidable. Notifying andcommunicating with buildingoperators is essential. Note thatthe most important factor is toprotect occupants. The buildingitself is of secondary importance.

DESIGN CONSIDERATIONSBefore applying any strategy

for damper control, the mechan-ical engineer must thoroughlyexamine the building require-ments. This involves studyinginformation garnered from stan-dards, codes, the owner, and ar-chitect. Above all, the engineermust determine if his or her vi-sion is physically possible orwhat changes might be neededto achieve it.

Code officials must becomeknowledgeable about the ex-ceptions to existing codes thatmay be necessary to achieveoverall design goals. There willbe a transition time beforecodes are adapted to anychanged circumstances.

The engineer needs to studyinformation including the build-ing components, zones and air-flow paths, normal movement ofpeople and materials into andout of the structure, occupancylevels, lobbies, elevators, parkinggarages, windows, doors, and ex-iting routes.

Most smoke is hot and willrise, while most CBR agents arelikely to be particulate oraerosols that move with standardventilation air. Gas tracer testswill help determine what designtactics need to be employed.Smoke generators produce coldchemical smoke, which is appro-priate for simulating chemicalairflows.

Hazard analysis includeswind, make-up air, short-cir-cuiting of airflow from supplyto return diffusers within abuilding or from exhaust to in-take louvers outside the build-ing, VAV fan involvement withpressure differences and instairwells, mechanical exhaust,and the general complex air-flows of any building.

Figure 3 depicts the airflowsinvolved in a single-zone VAVsystem with a central return.Any strategy to contain trans-port of a contaminant in thespace served while the fanscontinue to run will fail withthe exception of areas immedi-ately pulled negative by ex-haust fans. Contamination ofthis space from others couldeasily occur due to pressure dif-ferences from other air han-dlers, piston action by the ele-vators, or stack effect.

TACTICSDepending on the specific air

handling systems, different tac-tics may be applied.

Small office building

Highrise

Interlockedmultibuilding

complex

FIGURE 1. Range of building size and complexity.

FIGURE 2. Interpenetrating air systems.

4 Homeland Security In Buildings Month Year

Tactic: Shelter in PlaceAll fans are shut down and

the smoke control dampers areclosed. This passive protectionmethod is the default tactic incases where it’s impossible tomake informed decisions andwhere the CBR release hastaken place outside of thebuilding.

Benefits:Existing switches on the fire

fighters’ control panel can beemployed. Cross training ofpolice and fire fighters is possi-ble; each can possess keys. Po-lice are on patrol and are gener-ally expected to be in abuilding sooner.

Tactic: Zone IsolationThe contaminated zone or

zones are shut down while theother zones are left running. Adefault zone is a single floor.One zone or floor should beevacuated while the others arepressurized.

Benefits:Not all fire-fighting stations

have individual Hand-Off-Auto switches for each air han-dler. Retrofits using networkedcontrols allow a relatively inex-pensive method to gain con-trol. Floor dampers are not re-quired in most existing codes.

Where DDC has been in-stalled, only slight modifica-tions should be necessary toachieve goals. NOTE: Oldpneumatically controlledbuildings may need extensivemodifications.

Tactic: Zone PressurizationA contaminated area can be

isolated by use of smoke controldampers. Air handlers may beshut down as necessary. Typi-cally, only the contaminatedzone is exhausted, and the adja-cent zones are placed in full sup-ply with exhausts closed.

Benefits:Where full smoke control

systems exist, this is the idealmethod. The control panellends itself to isolation withoutmodification. Hand-Off-Autoswitches already exist. Testswitches allow for good mainte-nance checks.

ENHANCED PASSIVE PROTECTION &OTHER APPROACHES

In situations where the sys-tem is well understood, the sys-tem may be used in special op-eration modes. For example, aunit known to be far from anysource of contaminant can beput into 100% outside air in-take as a source of clean air. In-termediate units may be shutdown or VAV box dampers inselected zones may be run fullclosed. Then, units near an ex-ternally released contaminantmay be put in return air or relieffan only. This puts a positivepressure on both the outside airintake and exhaust air dampersto keep contaminants from en-tering.

Use of the DDC system re-quires knowledge of the opera-tions and access codes. Policeand fire fighters cannot make useof them without trained station-ary engineers or building secu-rity personnel present. Trainingand operation procedures for

Complexity of Airflows

5-15%Duct

leakage

5-15%Duct leakage

Mechanicalexhaust Exfiltration

Stack effect

Elevatordoors

Other airhandlers

Combustion airinfiltraion

REARAFRP

RAMA SAF SA

VAV

EA

OAWind

VAV VAV

EA = Exhaust airMA = Mixed airOA = Outside airRA = Return air

RP = Relief plenumREA = Return-exhaust airSA = Supply airRAF = Return air fan

SAF = Supply air fanVAV = Variable air volume box

SA RA

Opendamper

Closed damperPressurized zone

Opendamper

Closed damperPressurized zone

Closeddamper

Open damperSmoke zone

FIGURE 3. The airflows involved in a single-zone VAV system with acentral return.

FIGURE 4. Floor isolation or smoke dampers at shaft penetrations insandwich pressurization systems can be used for both smoke controland CBR isolation.

Month Year Homeland Security In Buildings 5

each building may be easily es-tablished. The will to performadequately must be important tomanagement.

VAV zone dampers may beemployed in zone isolation. Co-ordination between police ormaintenance people physicallyon floors with the DDC controloperator is possible. Given themissing drawings, deferredmaintenance, tight facility budg-ets, and lack of will by manage-ment in many buildings, build-ing codes will be necessary toenforce operational procedures.It may be more realistic to in-

crease occupant awareness,which would put pressure onmanagement to perform well.Prescriptive codes are not recom-mended; performance and flexi-bility are needed.

Police, firefighters, and build-ing operators must think strate-gically before taking action. Re-flexively shutting down all airhandling units might cause moreproblems than allowing pressur-ization and exhaust to continueto clean the air. Placing systemsin smoke mode may spread toxicagents if the improper mode is

selected. Elevator doors may beopen intentionally in smokemode. Some fire procedures areinappropriate – such as recall ofelevators to the ground floor.

An emergency official whohas just entered the building forthe first time would not knowhow to apply the the correct tac-tics.

DAMPER CONSIDERATIONSClass I AMCA licensed low

leakage dampers should be in-stalled on all change-outs inbuildings and in new construc-tion. The higher leakage Class II

and III presently allowed incodes and standards are not ap-propriate and save very littlemoney. Older class IV dampersleak excessively. (Leakage rateddampers are typically the fire andsmoke combination damperswith UL555 and UL555S list-ing.2)

Economizer and floor isola-tion dampers need not necessar-ily be listed, but leakage rateddampers should be considered.The higher quality dampers canbe used with standard modulat-ing actuators.

Where an air handling unit isto be used for exhausting smokeor CBR contaminated air, thepossibility of contamination ofoutside air via the recirculationair duct needs to be examined.

The relief fan system cannotcross contaminate the outsideair. The return air system couldcontaminate the supply air. Theoutside air and relief fan or ex-haust air dampers are of no con-cern.

Floor isolation or smokedampers at shaft penetrations insandwich pressurization systemscan be used for both smoke con-trol and CBR isolation (see Fig-ure 4). (NOTE: Smoke controlsystems may not be effective onheavy chemical agents, whichwill tend to sink, unlike smoke.)

CONTROL PANELSThe design and style of the

fire fighters’ control station willvary, but it must be clearlymarked and easy to use (see Fig-ure 5 for an example). Anythingmore complicated would requirestudy to achieve expert control.

A “kill switch” could be addedto any panel to allow singleswitch shut down of all systems.The flexibility of the individualswitches is preferred so that se-lective strategies could be ap-plied.

Again, operators should haveprepared plans for differenteventualities. The probable op-erators of the system are notpressure control experts.

Individual control of every fi-nal element can be expensive,particularly in large complexbuildings (and if there is toomuch information, no one willbe able to use it anyway). Atrade-off between cost and po-tential benefits must be consid-ered. Reasonable balance can beengineered into the system.

Most control systems have noindicator lights. In many, wherelights are included, an entirezone or floor is indicated on onelight. The proximity switches,auxiliary switches on the actua-

OnAutoOff

OnAuto

Off

OpenAutoClosed

Supply air fan Return air fan

SAdamperfloor 5

OpenAutoClosed

SAdamperfloor 4

OpenAutoClosed

SAdamperfloor 3

RAdamperfloor 5

RAdamperfloor 4

RAdamperfloor 3

OpenAuto

Closed

OpenAuto

Closed

OpenAuto

Closed

Light on Switch

Indicator lights with each switch would allow better knowledgeof actions.

FIGURE 5. The design and style of the fire fighters’ control stationmust be clearly marked and easy to use.

6 Homeland Security In Buildings Month Year

tors, or damper blade whiskerswitches are wired in series withthe light.

As a monitoring system forzone smoke control, switches arecost effective and provide an ef-fective maintenance and com-missioning tool.

OTHER CONSIDERATIONSWhile there are many details

worth discussing that are beyondthe scope of this article, here aresome final thoughts.

The economizer sequence ofoperation and the damper con-trol may be under fire alarm-iso-lated hard-contact relay control.In that case, the alarm panelmust be able to operate dampers.The alarm company is rarelyqualified to interface directly.The consultant’s drawings mustindicate who is to provide whatwiring at which terminal strip toseparate trades or responsibili-ties.

If the economizer is under to-tal control of the temperaturecontrol DDC system, then aclear sequence must be achiev-able via interface switches. If wa-ter coils can freeze, then the se-quence in event ofpurge-evacuation must protectthe coil by opening valves. (Thedesign must consider every de-tail and provide 3-way valves andrunaround pumps if necessary.)

System maintenance is aproblem in most buildings.With budget constraints, opera-tional checks are deferred untilfailure. Building owners, station-ary engineers, and occupantsmust become knowledgeableabout safety within the buildingand take responsibility. Institut-ing a training program or ap-pointing a task force or reviewcommittee might be a goodstart.

While CBR threats exist, it islikely that fire is still a biggerthreat to a building’s occupants.The smoke control system’s pri-mary purpose is to allow peopleto escape in case of a fire. Thatgoal should not be compromised

by other security efforts.

CONCLUSIONUse of an existing smoke con-

trol system may allow for low-cost mitigation of the effects of aCBR attack. However, not everyattack can be prevented, nor cancontrol systems totally protectoccupants. Placing isolation,economizer, and smoke controldampers under control of thefire fighters’ station may helpprotect occupants.

To more of a degree than inthe past, the architect must de-sign the building from the insideout. Airflow becomes a more im-portant factor in building designand is not just the mechanicalengineer’s responsibility.

Given ASHRAE energy andIAQ standards for design, theneed for smoke and fire protec-tion, and additional security is-sues, the mechanical systems in abuilding must be given high pri-ority and a greater share of budg-ets.

At the same time we recognizethe purpose of commercialbuildings is to provide healthy,comfortable, productive envi-ronments, and engineers and ar-chitects must cooperate with oneanother to reach these goals.

FOOTNOTES1) Klote, J.H., D.Sc., and J.A.

Milke, Ph.D. 2002. Principles ofsmoke management. ASHRAESpecial Publications, W. StephenComstock, publisher.

2) See www.amca.org/crp/products/index.asp and selectdampers for certification infor-mation.

REFERENCESAMCA. Fire, ceiling and

smoke dampers application man-ual. Air Movement and ControlAssociation, Publication 503-93. www.amca.org/about.asp.

ASHRAE. January 2003.“Report of presidential ad hoccommittee for building healthand safety under extraordinaryincidents on risk management

guidance for health, safety andenvironmental security underextraordinary incidents.”http://xp20.ashrae.org.

Corley, W.G. September2002. “Fireproofing critical forpotential targets.” Building De-sign & Construction.

Cosiol, J., PE. September2002. “Interfacing buildingHVAC controls and life-safetysystems after 9/11.” HPAC Engi-neering.

Goldrosen, P.M., PE, andA.E. Everhart. February 2002.“From interface to integrate.”Consulting-Specifying Engineer.

Klote, J.H., D.Sc., and J.A.Milke, Ph.D. 2002. Principles ofsmoke management. ASHRAESpecial Publications, W. StephenComstock, publisher.

Licht, R. 2002. “Balancingactive and passive fire protectionsystems in the building codes.”www.afscc.org.

Horwitz-Bennett, B. April2003. “The model for smokecontrol.” Consulting –SpecifyingEngineer.

NIOSH. April 2003. “Guid-ance for filtration and air-clean-ing systems to protect buildingenvironments from airbornechemical, biological, or radiolog-ical attacks.” www.cdc gov/niosh/docs/2003-136/pdfs/2003-136.pdf.

ABOUT THE AUTHORLarry Felker is a mechanical

engineer and fire and smokeproduct manager for BelimoAircontrols (USA), Western Re-gion, Sparks, Nev. He was for-merly vice president of engineer-ing for a Chicago controlsdistributor and technical man-ager for the western U.S. for Be-limo. He also has experience insales and training management.

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