the application of performance- based design …/media/files/forms and premiums/101 handbook...1208...

Over the past several years, a more formalizedapproach to the equivalency concept has been devel-oped. This approach is often referred to as perfor-mance-based design. Both the Society of FireProtection Engineers (SFPE) and NFPA have devel-oped guidance documents in this regard.1,2 As notedin Chapters 4 and 5 of the Life Safety Code, perfor-mance-based design is now specifically addressedand permitted by NFPA 101 as well as NFPA 5000�,Building Construction and Safety Code�.3

The application of performance-based design forfire safety should include a risk analysis to identifythe types of fires to be considered. This is an im-portant step, as the threat to occupants by fire needsto be identified and quantified if an appropriate firesafety solution is to be developed. Traditional build-ing regulations do not identify the fire hazard against

S U P P L E M E N T 7

The Application of Performance-Based Design Concepts for Fireand Life SafetyMilosh Puchovsky, P.E.James Quiter, P.E.

Editor’s Note: This supplement provides a brief overview regarding the application ofperformance-based design approaches for fire and life safety. Specific examples regardingegress, occupant loading, structural fire protection, smoke management, and sprinklerprotection are addressed.

Milosh Puchovsky, P.E., is a principal fire protection engineer with NFPA, where heoversees NFPA’s projects on Performance-Based Codes and Fire Risk. He also serves asstaff liaison to a number of technical committee projects, including those responsible forNFPA’s Building Construction and Safety Code and Life Safety Code. Milosh also overseesNFPA’s High-Rise Building Safety Advisory Committee.

Jim Quiter, P.E., is a principal of Arup and the leader of Arup Consulting in the UnitedStates. He is also chair of the Safety to Life Technical Correlating Committee and a memberof the NFPA 5000� Technical Correlating Committee, as well as Chair of the NFPA High-Rise Building Safety Advisory Committee. Jim is a registered professional engineer inseveral states.

The application of performance-based design con-cepts has been permitted by various codes and stan-dards through equivalency or alternative means ofprotection provisions. Initially, the overall conceptwas to allow for the use of alternative approaches ortechnologies in meeting the intent of the code. Assuch, equivalency concepts were pursued where thecode did not specifically address a given situation, orwhere priority was given to a design concept thatcalled for a building arrangement or feature that wasnot in strict compliance with the prescriptive provi-sions of the code. While the equivalency approachhas been implemented for decades, no guidance orestablished approach existed that would aid the de-signer or the enforcing authority in making appro-priate decisions about the equivalent means ofprotection.

1207

1208 Supplement 7 • The Application of Performance-Based Design Concepts for Fire and Life Safety

which the standard protects. In most cases, buildingregulations prescribe a solution to some unidentifiedor vague fire situation.

Performance-based design provides a more flexi-ble approach, allowing greater design freedom whilespecifically addressing fire and life safety concerns ofa specific building project. When properly applied, itprovides a more informed approach so that life safetyrisks can be more carefully addressed. Performance-based design also typically involves the use of com-puter fire models or other fire engineering calculationmethodologies, such as timed egress studies, to helpassess if the proposed fire safety solutions meet thefire safety goals under the conditions specified.

Although performance-based design can be ap-plied to any building project, it is most effective forcomplex and unusual structures, particularly thosethat do not fit well within the guidelines of prescrip-tive building regulations. Examples include conven-tion centers, shopping malls, airport terminals,transportation centers, and buildings with unen-closed vertical openings, all of which pose challengeswith regard to egress, spread of fire and smoke, anddetection and suppression. Museums and historicstructures also benefit from performance-based de-sign because the designers of these buildings mustbalance aesthetics and historic preservation with firesafety concerns, and building regulations do not usu-ally address property protection or historic preserva-tion. For similar reasons, industrial facilities withhazardous or sensitive processes and contents alsobenefit from performance-based design.

EGRESS FROM AN OBSERVATION TOWER

In developing the fire and life safety program for abuilding such as an observation tower with a largepopulation and amusement rides, numerous issuesneed to be addressed. The tower rises over 900 ft (274m) above grade, with eight occupied levels and twoamusement rides in the ‘‘pod’’ or upper portion ofthe tower. At the base of the tower is a casino building.Occupied floors of the pod include two levels of ob-servation deck, a restaurant, a meeting room level,wedding chapels, and a bar level. The top level func-tions as an amusement level, containing a rollercoaster and ‘‘space shot’’ ride. Exhibit S7.1 illustrateslevel 6 of the pod, which functions primarily as arestaurant. Exhibit S7.2 illustrates level 8 of the pod,which functions as the lower observation level. Ex-hibit S7.3 illustrates level 1 of the pod, which servesas one of two refuge areas.

The most obvious concern is providing for emer-gency egress, considering that the lowest occupied

floor is 795 ft (242 m) above grade. In accordance withapplicable regulations, some floors of the structurecould include an occupant load in excess of 500 peo-ple. Strict adherence to the Life Safety Code requiresthree remote exit stairs leading from the top of thetower to the base of the building. The physical areaof the supporting structure is not large enough toprovide remotely located stairs in accordance withthe Code, and the height of the building makes theuse of stairs as a means of egress somewhat impracti-cal. An alternative approach based on performance-based design concepts was necessary to develop aworkable egress strategy.

Exit Program

The primary evacuation method for this building isthe use of typical exit stairs for the occupied floors,discharging to areas of refuge on the lowest two floorsof the pod. In other words, from floors 3 through 10of the pod, three sets of exit stairs are provided, eachenclosed in 2-hour fire-resistant construction, just aswould be found in most other buildings. However,these stairs discharge to an area of refuge at the low-est two levels of the pod, which is still 750 ft (230 m)above grade. These two areas of refuge are used forno other purpose, and consist entirely of non-combustible construction. Rather than rely on me-chanical systems to maintain the areas of refuge freeof smoke in the event of a fire, the two floors areopen to the surrounding exterior environment so thatnatural ventilation occurs. Since the two areas arebelow the occupied levels, it is unlikely that a fire inan occupied level would spread to the areas of refuge.Additionally, all the floors including the areas of ref-uge are provided with sprinkler, standpipe, andalarm systems, further reducing the likelihood ofdownward fire spread. (Detectors are located on allfloors other than the open refuge floors.)

From the area of refuge, a single stair leads downthrough the shaft of the tower to grade. The primaryevacuation route from the area of refuge involves theelevators. These elevators have two levels and travelat a speed of up to 1,800 ft/min. They can dischargeeither within the main casino or at two specially de-signed discharge levels at the roof of the base build-ing. These discharge levels are enclosed in 2-hourfire-resistant construction from the roof to grade andare separated from all other areas by 2-hour fire-resistant construction.

Special Elevator Shaft Protection

To increase the reliability of the elevators and thesafety of the elevator car occupants, special protection

2006 Life Safety Code Handbook

1209Egress from an Observation Tower

3. Elevator lobbies are on a separate smoke controlzone to maintain pressurization with relation toadjacent spaces. Therefore, smoke in an adjoiningarea will not spread into an elevator lobby.

4. Openings into the elevators are slightly raisedfrom the remainder of the floor, preventing waterflow on a floor level from spilling into the elevatorhoistway.

5. Because the areas of refuge are at the two lowestfloor levels of the pod, the elevators will not needto travel past a fire floor. Elevators will travel onlybetween the areas of refuge and the base building.Areas of refuge for disabled persons are providedwithin the enclosed pressurized stairwells at eachlevel.

6. Elevator shafts are vented to the outside at thetop, and the vents are separate from the machinerooms. In addition, the machine rooms form sepa-

has been provided. The tower design was undertakenduring the same time period in which the NationalInstitute of Standards and Technology (NIST) wasinitiating studies on the use of elevators for buildingevacuation. Many of the recommendations developedby NIST have been incorporated as design conceptsfor the tower. The concepts include the following:

1. Elevators open into 2-hour fire-resistance-rated el-evator lobbies on all floors, at both the top and thebottom of the building.

2. There are four elevators that travel through theshaft from the base to the top. Two independentelevator machine rooms serve these elevators. Theelevator machine rooms are separated by 2-hourfire-resistant construction and have a 4-in. curbinstalled between them so that water flow in onemachine room will not affect the other.

Life Safety Code Handbook 2006

Exhibit S7.1 Observation tower, pod level 6.


rate smoke control zones, and air-conditioning forthe machine rooms is on emergency power.

7. All four elevators are on emergency power. Theemergency power riser is in a separate dedicated2-hour shaft.

8. Only three of the elevators are assumed to be avail-able for evacuation purposes. The fourth elevatoris dedicated for use by the fire department.

Stairs

In addition to the elevator evacuation, a single stairleads down through the tower and discharges tograde. The stair enclosure is pressurized and remainsindependent of the base building. Enlarged stairlandings at predetermined levels allow occupants tostop and rest as they descend through the building.In addition, the three stairs in the pod of the buildingare enclosed in 2-hour fire-resistant construction and

pressurized. Each of these stairs has areas of evacua-tion assistance, with communication capability to thecentral control room.

Occupant Load Determination

With a building of this type, it is important to under-stand and control the occupant load. Three methodswere used to determine occupant load. Once thethree calculations were performed, the lowest occu-pant load calculated was used as the limiting factorfor the building.

Areas of Refuge. Building codes and the Life SafetyCode typically allow holding areas or areas of refugefor horizontal exits. Where those holding areas areused, the codes require a minimum of 3 ft2 (0.28 m2)per person. Therefore, one of the limiting factors forthis building was the size of the areas of refuge. De-



1211Egress from an Observation Tower

of the entire building is limited by the size of thearea of refuge.

Code Calculations. The second means of determin-ing the occupant load of the building was based oncode calculations. The expected occupant load, basedon the applicable building code, was calculated foreach floor of the building. The load was then totaledfor the entire building, and this occupant load wasused as a limiting factor for the number of people inthe building.

Evacuation Capacity. The third determining factorwas the capacity of the elevators to evacuate occu-pants. The speed of evacuation was based on calcula-tion methods for elevator evacuation contained in

termining their maximum holding capacity providesa factor of safety for several reasons, as follows:

1. The area of stairs leading to the areas of refugewas not included in the holding area. These stairswould significantly increase the number of peoplethat could be safely accommodated within an areaseparated from the fire by 2-hour construction.

2. The calculations assume that no occupants areleaving the building via elevator or stair. Instead,they assume that all occupants are containedwithin the areas of refuge.

3. The evacuation scenario is to evacuate the floor oforigin, the floor above, and the floor below. There-fore, only a portion of the building would be simul-taneously evacuated. However, the occupant load




NIST studies. For this project, it was concluded thata 1-hour time frame was reasonable to fully evacuatethe areas of refuge. This 1-hour time frame was basedon three of the four elevators being used for evacua-tion, with the fourth dedicated solely to fire depart-ment use. The 1-hour calculation also ignores theavailability of the stair leading down through theshaft. Therefore, by this calculation, all occupants areexpected to leave via the three elevators. It shouldbe noted that operational considerations require theoccupant load to be further limited if one of the eleva-tors is out of service for repair.

Once these three methods of calculation werecompleted, an occupant load of approximately 2600people was developed as the expected load of thebuilding. This was the load factor around which theremainder of the building was designed. To ensurethat this load factor is not exceeded, the buildingowner has instituted an occupant counting systemthat keeps track of the number of people enteringand leaving the tower. Therefore, the load of thebuilding will not exceed the calculated occupant load.

A key aspect of the egress program is crowd man-agement during an incident. The tower staff have beentrained to direct people to the nearest stair and areasof refuge. Other staff have been trained to respond im-mediately to the area of refuge and to direct peopleto either the stair or the elevator queue. Railings areprovided to help establish queues at the elevators.Signage and floor path markings are also evident tohelp guide people arriving in the refuge area.

Other Features

The evacuation system was not designed as a stand-alone system. The fire protection features for the proj-ect were specifically designed to rapidly detect andcontrol a fire, to control smoke generated by likelyfires, and to ensure that a backup electric power sys-tem was available.

The building is completely protected with auto-matic sprinklers. Sprinkler densities exceed those re-quired by the codes. The sprinkler system wascalculated to provide a very high density for the firstfour sprinklers operating, plus ordinary hazard den-sity for the most remote 1500 ft2.

Water supply is from two pumps at street level,which pump up to the pod. There is on-site waterstorage within the pod and two additional pumpssized for sprinkler plus standpipe demand in the pod.With these pumps and on-site water storage, redun-dant water supply is available.

The building is fully protected with automaticsmoke detectors, except that kitchens contain heatdetection. The smoke detectors are on an addressable

system, with alarm verification to reduce the numberof unwanted alarms. Manual fire alarm boxes are alsoprovided in the facility. To reduce unwanted alarms,the boxes have been placed within the stairways.

The alarms report to the main central controlroom for the casino, as well as to two auxiliary controlrooms. One of the auxiliary control rooms is locatedat the base of the tower; the second is located withinthe area of refuge at elevation 750 ft (230 m). Thecontrol room within the area of refuge is accesseddirectly from the fire fighters’ elevator. Communica-tion and information flow from the three controlrooms is identical.

The fire alarm system is a Class A system, withseparate risers running up through the shaft. Therisers are separated by 2-hour fire-resistant construc-tion.

Emergency power is sized to accommodate allportions of the fire protection system, including thefire pumps, fire alarm system, all elevators, smokecontrol, and necessary lighting. The emergency powerriser is routed through a separate 2-hour shaft upthrough the tower, in order to prevent a single eventfrom impacting the primary and emergency power.

The building is provided with an automaticsmoke control system. Upon actuation of an alarm,the floor of origin and any floors open to it go tofull exhaust while adjoining floors are pressurized.In addition, the elevator lobbies for all floors are pres-surized, as is the stair leading down through the shaftof the tower. Exhaust from the smoke control systemis ducted to discharge above the ride level at the topof the tower, in order to eliminate reintroduction ofsmoke into the building.

The observation tower required a fire protectionapproach that departs from the typical building codeapproach to a building. Use of stairs as the sole evacu-ation method was not feasible or reasonable. Requir-ing all of the occupants to utilize stairs would resultin an unsafe condition for many of the expected occu-pants of this building. A more reasonable methodwas to provide an area where people could be stageduntil evacuated and a reliable means to perform thatevacuation. In this example, the performance-baseddesign approach was shown to provide protection inaccordance with the overall intent of the buildingcodes, while departing significantly from the detailedprescribed code requirements.

SPRINKLER PLACEMENT IN AN ARTGALLERY

The design concept for the upper floor of an art gal-lery called for a unique roof/ceiling structure con-


1213Sprinkler Placement in an Art Gallery

Locating sprinklers in the supporting grid at thebase of the pockets appeared to offer the best option.However, because of the depth of the pockets, thesprinklers would be positioned more than the dis-tance permitted by NFPA 13 from the top of the sky-light pocket. In this case, proper sprinkler spacingneeded to be determined.

Fire engineering employing computer fire mod-els offered an effective means of analyzing how sprin-klers would perform under the skylights. During afire, the skylight pockets, because of their depth andnumber, would serve as heat reservoirs and have animpact on sprinkler activation. How much of an im-pact would be a function of numerous factors includ-ing the design fire, fire dynamics, ceiling and roomgeometry, and sprinkler type, spacing, and position-ing. It is important to note that NFPA 13 only providesinformation on how to install sprinklers; it providesno information or criteria for how soon after the start

sisting of a grid of approximately 800 skylight pockets.NFPA 13, Standard for the Installation of Sprinkler Sys-tems,4 does not address the ceiling arrangement, anda fire engineering analysis was necessary to addressthe relevant fire safety concerns and develop appro-priate sprinkler positioning and spacing criteria.

The ceiling/roof structure consisted of a grid ofcircular skylight pockets extending approximately 60in. (1500 mm) from their base to their peak. The open-ing to the skylight pocket was approximately 42 in.(1070 mm) in diameter. The separation between adja-cent skylight pockets was approximately 14 in. (360mm), with the supporting members approximately48 in. (1200 mm) apart. The ceiling height (to the baseof the skylight pockets) was approximately 216 in.(5490 mm) from the floor below. A rendering of asection of the ceiling/roof arrangement is shown inExhibits S7.4 and S7.5.

Because of the depth, area, and arrangement ofthe skylight pockets, the specific rules of NFPA 13concerning sprinkler positioning were not directlyapplicable and did not adequately address the rele-vant fire and life safety concerns.

Locating sprinklers in each pocket was undesir-able in terms of both functionality and aesthetics.Locating sprinklers in the pockets would place themfarther away from the floor where a potential fire wasexpected to occur, prolonging the time to sprinkleractivation. Once activated, the sprinklers would notbe able to develop their proper spray pattern if posi-tioned in the skylight pocket; the result would be acolumn of water discharged from each skylightpocket. Also, locating sprinklers in alternating pock-ets would result in an unacceptable delay in sprinkleractivation unless the fire was located directly belowa skylight with a sprinkler.


Exhibit S7.4 Plan view of ceilingarrangement.

Section 1–1 Section 2–2

Section A–A

4 ft–0 in.

15 ft–6 in.

3 ft–10 in.

38 ft–1¹⁄₂ in.

Section A-A

3 ft –10 in.

17 ft9¹⁄₂ in.

38 ft – 1 ¹⁄₂ in.

Exhibit S7.5 Section view of ceiling/roof arrangement.


of a fire the sprinklers are to activate. It is understood,however, that sprinklers need to activate during theearly stages of fire development to be effective incontrolling the fire.

Computational fluid dynamics (CFD) was ap-plied to help understand the performance expectedfrom an NFPA 13–specified system, to quantify theassociated delay caused by the skylight pockets, andto help determine appropriate sprinkler spacing andpositioning to achieve the intent of NFPA 13. In thisregard, design fires representative of the fuel load inthe gallery were quantified, and acceptable sprinkleractivation performance criteria were determined.Sprinkler positioning and spacing appropriate tomeet the activation criteria for the design fires wereidentified. Exhibit S7.6 illustrates one scenario mod-eled and analyzed using Fire Dynamics Simulator, aCFD computer fire model developed and maintainedby NIST.

The overall approach was to establish design firesrepresentative of the types of fires expected in thegallery space. Various ceiling/roof arrangements per-mitted by NFPA 13 were then evaluated, using CFDcomputer models for the specified design fires, todetermine sprinkler activation times. These activa-tion times were established as acceptance criteria.Various sprinkler spacing configurations under theroof structure proposed for the upper gallery were

evaluated to determine those that would result in atime to sprinkler activation that was less than thatestablished as the acceptance criteria.

The analysis established sprinkler activation timecriteria for ceiling arrangements addressed by NFPA13. Three cases (smooth, flat ceiling; ceiling channels;and ceiling grid) were evaluated for the types of firesexpected in the gallery. The maximum sprinkler spac-ing and maximum distance between the sprinklerdeflector and ceiling were evaluated to determineacceptance criteria.

The engineering analysis included several factorsthat allowed a degree of conservatism to account foruncertainties in both the analysis and the forthcom-ing installation process and allowed some flexibilityin potential future modification of the design concept.These factors included the following:

1. Using ceiling heights less than that proposed forthe upper gallery in the determination of accept-able criteria as allowed by NFPA 13. This createdshorter sprinkler activation times.

2. Spacing ceiling members closer than the maxi-mum permitted by NFPA 13 in the determinationof acceptable criteria. This created shorter sprin-kler activation time.

3. Establishing a design fire with higher rates of heatrelease than those for the types of combustibles


Exhibit S7.6 CFD analysis ofsprinkler activation.

1215Life Safety for a Botanical Garden Project

and the methods of fastening. The analysis indicatedthat the structural elements could withstand the re-spective fire loads represented by the design fires forthe time period associated with the code-prescribedfire resistance rating.

To account for a degree of uncertainty and toprovide for a factor of safety, it was proposed thatthe spacing of the structural members supporting thewalkways and roof structure be decreased from whatwas initially specified, resulting in some redundancyof the structural support system. The effect of thisarrangement was that, should a given structuralmember prematurely fail, there was a reduced likeli-hood that the entire structure would fail. Thus, it wasdemonstrated that the conventional fire resistancerating of the structural elements could be achievedthrough other means, and that an equivalent meansof protection could be provided for the anticipateddesign fires. A timed egress study was also under-taken to verify that occupants could evacuate fromthis space before the building structure suffered anynegative effects from the fire.

An approach based entirely on prescribed coderequirements does not specifically consider buildingperformance or occupant response under expectedfire conditions. Building codes consider classes ofbuildings generically and do not address specific firehazards, unique building features, and occupantcharacteristics. As a result, code-prescribed solutionscan provide for excessive fire protection in some in-stances and inadequate protection in others. With aperformance-based approach, the architects in theuniversity student center project were able to imple-ment their design vision while adequately addressingapplicable fire safety concerns.

LIFE SAFETY FOR A BOTANICAL GARDENPROJECT

The design of a botanical garden project consistingof multiple floor levels carved into the surroundinghillside presented unusual challenges for fire and lifesafety. The project entailed a freestanding structurereaching 180 ft (55 m) at its highest points and coveredan overall area of 5.4 acres (21,853 m2). From the out-set, it was clear that a prescriptive code approachwould be of limited value for the project.

The applicable building regulations classified thestructure as an assembly occupancy, but if the projecthad been designed to fit the requirements of the pre-scriptive code, the design team would have beenfaced with trying to make the building conform torequirements derived from safety measures intendedfor theaters, arenas, and other more conventional

typically expected in the gallery. This flexibilityallowed for contents that might be present in thegallery for special exhibits and functions.

The analysis of the gallery roof structure indicatedthat a sprinkler spacing arrangement could be devel-oped that would result in a sprinkler activation timeshorter than that derived from NFPA 13. A perfor-mance-based approach was used to develop a meansof protection equivalent to that prescribed by NFPA13.

STRUCTURAL FIRE PROTECTION FOR ASTUDENT CENTER

One of the design objectives for a university studentcenter project was to create an open and unclutteredfeel for the atrium. The intent was to use exposedslender structural steel elements to support theglazed facade, the circulation ramps, and the roof.

According to the applicable building regulations,the structural elements in the atrium needed to havea certain fire resistance rating. Conventional methodsof achieving such a rating — such as cladding orcoating the structural members with a cementitiousmaterial or intumescent paint — would have beeneffective but would have diminished the desired ar-chitectural effect and negatively affected overall proj-ect functionality.

A performance-based design approach wasdeveloped as an equivalent means of meeting thebuilding code requirements. A code analysis was con-ducted, and a fire strategy outlining the approach toresolve the relevant issues was prepared. The con-cerns of the associated stakeholders, including thelocal enforcing authorities, were identified and artic-ulated, as were the design fires and criteria for de-termining acceptance of the alternative design.

Risk analysis principles were used to determinethe likely fire hazards expected in the atrium space.Design fires were developed to quantify the relativesize, duration, and characteristics of the fires antici-pated. At the same time, the failure criteria — in termsof fire resistance — of the structural steel membersproposed were also determined. It was agreed thatthe alternative design would need to withstand theimpact of the design fires for a minimum time periodof hourly fire resistance rating specified by the build-ing code.

The performance of the structural steel memberswhen exposed to the specified design fires was evalu-ated through the use of modeling and with the collab-oration of structural engineers. The analysis includedthe effect of the structural member composition, aswell as the means and spacing of structural supports



public buildings. The relevance of the prescriptiverequirements was clearly limited for the project —there was no ‘‘rule book’’ to follow.

Early on in the design project, it was proposedthat fire and life safety provisions be developedthrough performance-based design. This was dis-cussed and agreed upon with the client and the localbuilding and fire authorities.

The fire hazards in a building like this are verydifferent from those typically encountered in conven-tional buildings. The vegetation clearly constituted afire load, potentially an extremely large one, so thepotential for a forest fire-type scenario was discussed.The team carried out a qualitative hazard analysis ofthe risk — in terms of frequency and consequences— of a vegetation fire in the structure, but this showedsuch a fire to be of sufficiently low probability thatit was an impractical design parameter.

The examination of fire loading, therefore, turnedto items other than the vegetation. Throughout thestructure, huts are provided as information points forvisitors. The huts are built of timber, with thatchedroofs, and also have electrical power. Scenarios in-volving a fire in a hut were therefore developed asthe basis for the fire safety design.

Because large visitor populations were antici-pated, safe and efficient evacuation was a key concernin developing the fire strategy. The circulation (and,hence, evacuation) routes are far from conventional,as visitors walk around the botanical gardens onwinding pathways linked to exits around the perime-ter. Also, because the structure cuts into the hillside,pathway elevations vary considerably. A major chal-lenge was to address the scale of the building, re-flected in the length of the travel routes. If traveldistance requirements of the building regulationswere to be met, escape from the upper parts of thestructure would require tunnels cut through the sideof the hill. Such tunnels would probably need to havebeen pressurized, as they would have been at theupper levels of the project near potential smoke lay-ers. Other options were needed.

The fire engineers proposed that evacuation bebased on the time period necessary to egress thebuilding rather than strictly on the distance to betraveled. The approach was to demonstrate that occu-pants could egress the facility prior to the onset ofuntenable conditions. The majority of the exits werelocated on the lower grades of the project, so, in theevent of a fire, the occupants would travel to lower-level exits rather than use exits at the top of the botan-ical garden. Lower-level exits were also preferred asthey encouraged the population to move away from

the upper levels, where smoke would accumulate.While this route would result in evacuation distancesof up to 450 ft (137 m), these distances were demon-strated to be acceptable due to the overall low levelof hazard and large size of the space.

To verify the proposed strategy, combined smokeand evacuation calculations using computer modelswere undertaken. Based on the design fires, this al-lowed for a dynamic fire and smoke spread analysisof the actual geometry of the space. The timed egressstudy also considered various scenarios, such as theeffect of blocked exits.

Due to the structure’s unique geometry, conven-tional smoke modeling software packages — whichassume rectangular ‘‘box-type’’ enclosures — wereunsuitable for calculating the rate of smoke fill. Proj-ect-specific calculations were therefore developedthat allowed for the geometry of botanical gardenspaces, using a three-dimensional model of the struc-ture. From the model, it was possible to accuratelydetermine the cross-sectional plan area of the projectat various heights, and hence assess smoke fillingrates using design fire scenarios agreed upon withthe local authorities.

The egress modeling showed that the projectcould be evacuated in 5 to 6 minutes, while the smokemodeling indicated that a smoke layer would not de-scend to levels where it would impede evacuation for15 to 25 minutes (depending on the fire scenario).The team concluded that the escape distances couldbe safely extended and evacuation conditions wouldbe acceptable under the conservative scenarios stud-ied.

Many fire safety systems conventionally associ-ated with public assembly spaces were unsuitable.Detection methods including optical and aspiratedsmoke detection were found to be ineffective, due tothe potential for smoke stratification to delay detec-tion at high levels and plants obscuring optical detec-tion sight lines.

Although the associated structures are essentiallylow fire hazard spaces, the fire safety strategy had tobe developed from a common-sense, first principlespoint of view. The recognition that there was littlerelevant guidance for the project, and that adherenceto conventional codes would result in unnecessary,costly, and ineffective measures, unlocked the designprocess. Close collaboration with the architect, en-forcement officials, and other engineering disciplinesallowed each team member to fully participate indeveloping the design and clearly understand thethought process and reasoning behind the proposedstrategy. The result is a simple, robust, and cost-


1217Cultural Preservation of a Historic Building

required level of safety. In historic landmark build-ings, this integrated approach typically results in im-proved building functionality and more cost-effectivefire protection systems.

One of the major fire and life safety challengesin this courthouse building pertained to the compart-mentation of building spaces. Building regulationsrequire compartmentation to help prevent the hori-zontal and vertical spread of fire through the build-ing. The existing building construction did notprovide for the rated fire separations required bybuilding regulations. Many doors were of originalheavy wood construction with decorative wood andglass features and did not meet current fire protectionratings. It was proposed that the atrium remain opento multiple floors, existing non-rated shafts be reusedas mechanical shafts, and certain building areas beopen to each other through open stairways.

In developing an appropriate strategy, the aimwas to assess the inherent fire protection qualitiesof existing building features (such as substantiallyconstructed walls and high ceilings), to take advan-tage of the inherent degree of fire protection, and tosupplement it with certain new active systems wherenecessary. The overall approach was to identify thefire loads (design fires) to be considered and thendemonstrate through fire engineering that sufficientfire safety could be provided for the time period in-tended by the building regulations. In some cases, itwas determined that the prescribed fire resistancerating would be needed; for other situations, a perfor-mance-based solution was developed.

In general, a fire that starts in the non-publicareas is to be controlled so that it does not developand grow to a point where it could threaten occupantsin public spaces. Therefore, it was proposed that non-public areas — the attic and basement, mechanicalspaces, and kitchens — be separated from publicspaces by fire-rated construction. Additionally, areastraditionally constituting a higher fire hazard, suchas electrical switch gear rooms, mechanical rooms,and storage areas, were also constructed to form sep-arate compartments. As most of these spaces werenon-public spaces, the new construction had a lim-ited impact on the aesthetic features of the building.

In addition to compartmentation, other fire andlife safety issues were identified and addressedthrough a performance-based approach. Issues re-garding smoke management, egress, structural fireresistance, active systems, and fire-fighting facilitieswere addressed in a comprehensive manner. Theoverall fire safety solution integrated existing fea-tures with new systems and construction so that the

effective strategy that provides a high level of firesafety for the botanical garden’s occupants.

CULTURAL PRESERVATION OF A HISTORICBUILDING

For historic structures, performance-based designconcepts often offer the most viable and effectivesolution for meeting both fire safety needs and cul-tural preservation goals. One such project was a des-ignated landmark building consisting of cast iron anddecorative masonry construction with ornate publicand ceremonial spaces centered around an openatrium. The building was originally constructed inthe mid-1800s to operate as a courthouse. It consistedof approximately 150,000 ft2 (14,000 m2) over severalfloors.

The proposed design concept for the courthousebuilding called for a comprehensive, government-funded restoration and rehabilitation program to pre-pare the building for adaptive reuse as a multifunc-tional public and cultural facility with exhibitionspace, offices, and a restaurant. The design conceptfor the project called for the preservation of a numberof areas and building features, including the openatrium, the ornate original wood doors, and numer-ous cast iron columns.

Although building code requirements are relaxedsomewhat for specific features of historic structures,imposing the applicable prescriptive requirementson the project would have affected the overall historicauthenticity and compromised the functionality andsignificance of the public spaces and unique architec-tural features. Therefore, the overall fire strategy wasto identify and meet the intent of the applicablebuilding regulations regarding life safety, while min-imizing the aesthetic and visual impact of new con-struction and maintaining the open environment andoriginal design features to the greatest degree possi-ble. During the early stages of the development of thefire strategy, it became obvious that a conventional,prescriptive code-based approach would have forceda dramatic change to the proposed design conceptand that an alternative approach could provide for amore effective and robust level of fire and life safety.

In most code-mandated prescriptive designs, thevarious fire safety features and systems are addressedindependently of one another. The performance-based concept calls for an integrated approach of fireand life safety systems. Such an approach is espe-cially pertinent to existing and historic building proj-ects because it can result in less intrusive fire andlife safety systems and features while meeting the



level of safety provided by the building code wassatisfied, while preserving the historic value of thebuilding to the extent possible.

CLOSING REMARKS

While considered by some a relatively new approach,performance-based design has been practiced formany years through the equivalency option in manycodes and standards. The past several years have seenthe development of a more formalized approach forpracticing performance-based design, as well as therevision of codes and standards that specifically ad-dress performance-based design approaches. Evenso, where a performance-based design is pursued, itusually involves a variance by the local building offi-cial or regulating body. However, the developmentof guidelines and definitions of applicable termsserves to better facilitate the discussion between de-signers and enforcers and allow for better-informeddecisions.

This supplement has provided a brief overviewof the types of projects in which performance-baseddesign has been successfully applied and acceptedby the authorities having jurisdiction. Even thoughperformance-based design is gaining more accep-tance, the prescriptive code is likely to remain thefirst means of developing a fire safety strategy for abuilding. Enforcing authorities have a greater comfort

level with the prescriptive rules that are, in essence,the law. As such, code reviews and interpretationsare often the first step in developing the fire safetydesign process.

For certain projects or for specific aspects of proj-ects, the prescriptive code does not adequately ad-dress a given situation or would be incompatible withthe developer’s or architect’s design vision. In othercases, a more cost-effective alternative would resultin the same level of protection as that required bythe prescriptive building code. In such cases, perfor-mance-based design concepts can be used to developsolutions that address specific issues while comple-menting the requirements prescribed by traditionalbuilding and fire codes.

REFERENCES

1. The SFPE Engineering Guide to Performance-Based FireProtection Analysis and Design, Society of Fire Pro-tection Engineers, Bethesda, MD, 2000.

2. Performance Based Primer for Codes and StandardsPreparation, National Fire Protection Association,Quincy, MA, 2000.

3. NFPA 5000�, Building Construction and Safety Code�,2006 edition, National Fire Protection Association,Quincy, MA.

4. NFPA 13, Standard for the Installation of SprinklerSystems, 2002 edition, National Fire Protection As-sociation, Quincy, MA.


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