Passive fire protection offers safety measures
A passive fire protection system, while sometimes omitted, is vital to occupants’ life safety
- Learn about the difference between passive and active fire protection systems.
- Understand what fire protection engineers and design professionals are responsible for in fire/life safety system design.
- Consider how passive fire protection systems can contribute to safety.
The level of fire safety in a building is only as good as its weakest link. Prescriptive codes establish minimum fire and life safety requirements, which include various active and passive fire protection features and systems. U.S. building and fire codes are written so as not to rely solely on any single safeguard, but rather multiple safeguards to mitigate an event where any single safeguard is rendered ineffective. See NFPA 101: Life Safety Code, 2018 edition, 4.5.1, in which “multiple safeguards” are outlined.
On Friday, Feb. 18, 2021, a fire occurred at a Hilton Garden Inn in Killeen, Texas. The hotel was fully occupied by families displaced during the period of extremely cold temperatures that resulted in power outages, water disruptions, food shortages and other complications. Media reports shortly after the fire indicated that the water in the sprinkler system pipe was frozen, rendering the system impaired.
While there are conflicting reports as to how the occupants became aware of the fire, all of the occupants were able to evacuate the four-story hotel without any major injuries. Before the fire was brought under control by the fire department, portions of the roof of the hotel were consumed by the fire or collapsed into the fourth floor. Would the outcome have been the same if the corridors did not have a fire-resistance rating and the exit stairs were not enclosed in fire-resistance rated construction?
It is anticipated that a more detailed investigation will identify the lessons to be learned from the fire incident, but initial reports indicate that the “additional” code-required safeguards contributed to the lack of serious injuries in this fire incident.
A properly designed, installed and maintained sprinkler system can be a very effective means to improve fire and life safety in such buildings. However, in this instance in which the sprinkler system was compromised, the additional, passive fire protection features contributed to the level of safety provided to the occupants in the building.
Fire codes, documents
Before building and fire codes required automatic sprinkler systems to the extent required by modern codes, the codes contained differing requirements for buildings protected with automatic sprinkler systems. “Sprinkler trade-offs,” as they were commonly called, were intended to reduce the cost of passive fire protection features to help offset the cost of the sprinkler system and encourage owners and developers to install sprinkler systems in buildings.
These concepts remain in modern codes in those occupancies in which sprinkler protection is not required. Based upon height, area, type of construction and occupancy classification, there are a number of buildings for which sprinkler protection is not mandatory and therefore the “sprinkler trade-off” concept would apply.
FAIL-SAFE, a National Association of State Fire Marshals Fire Research & Education Foundation project, was charged with establishing valid scientific information to serve as a baseline for understanding the effects of incorporating safety layers into the built environment. Project FAIL-SAFE was not a discussion advocating one product over another or active versus passive, but rather it was a discussion around safety and resiliency of the built environment.
In short, Project FAIL-SAFE was a research project designed to evaluate existing levels of redundancy to determine acceptable levels of safety should any individual system within the protective envelope fail to function as designed.
One of Project FAIL-SAFE’s endeavors was to commission a comprehensive literature review of sprinkler trade-offs prepared by the department of fire protection engineering at Worcester Polytechnic Institute. Major findings from the literature review include:
- Many provisions in the current prescribed codes are empirical.
- Many sprinkler trade-offs are scientifically baseless.
- Many sprinkler trade-offs for fire-resistance ratings are only partly supported by research using probabilistic risk analysis methods.
- Sprinkler trade-offs for exterior wall’s unprotected opening area could be implicitly verified by fire tests designed to study the interactions of sprinklers with smoke layer behaviors.
- Sprinkler trade-offs for travel distance/dead end length are potentially not well founded, as sprinklers fail to improve the tenability criteria of visibility, although sprinklers could be very effective in improving other tenability.
After completion of the literature review, the NASFM Foundation proceeded to the second phase of Project FAIL-SAFE and commissioned WPI to perform the computer modeling. The modeling was designed to address the following issues:
- A comparative analysis of fire protection system impacts on fire behavior, occupant survivability and structural resiliency.
- Evaluate three major sprinkler trade‐offs including egress, unprotected opening area and fire-resistance rating.
The modeling assumed a multifamily residential occupancy (Use Group R-2 as defined in the International Building Code) built of combustible construction (types VA and VB as defined in the IBC), both with and without sprinklers present and functioning.
The conclusions and recommendations from the modeling effort were:
- The single largest impact on occupant egress survivability is compartmentation of smoke and multiple egress routes.
- Minimum fire separation distance should be kept no less than 6 feet.
- The size of the unprotected opening area has little relevance on building-to-building fire spread; separation distance and exterior flammability are the key factors.
- Fire-resistance rating findings show fire will demonstrate more robust spread horizontally through fire separations between apartment units than vertically from one apartment to another.
- A hybrid performance/prescriptive approach to structural stability should be pursued to enhance fire-resistance rating features.
Role of the design professional
Clearly, design professionals need to design projects to at least comply with the minimum requirements of the applicable codes. The preamble to the National Society of Professional Engineers code of ethics states:
“Engineering is an important and learned profession. As members of this profession, engineers are expected to exhibit the highest standards of honesty and integrity. Engineering has a direct and vital impact on the quality of life for all people. Accordingly, the services provided by engineers require honesty, impartiality, fairness and equity and must be dedicated to the protection of the public health, safety and welfare. Engineers must perform under a standard of professional behavior that requires adherence to the highest principles of ethical conduct.”
Certain court decisions in the United States have resulted in a determination that merely designing a building to comply with the minimum standards of an applicable building or fire code may not be an adequate standard of care for design professionals.
Regardless of whether a design professional determines that the minimum code requirements are adequate or additional safeguards are required to meet the client’s goals and objectives, the same level of care should be devoted to passive fire protection features.
Construction document preparation
Years ago, it was not uncommon to review a set of construction documents that included a note that the building would be protected with an automatic sprinkler system or a fire alarm system. There would be a generic section in the specification to include additional requirements regarding applicable standards, allowable manufacturers, installation requirements and acceptance testing.
Today a set of construction documents are more likely to be more comprehensive and will include engineering design documents, water supply information, preliminary hydraulic calculations, occupancy hazard or commodity classifications and other aspects of the design.
However, when it comes to protecting penetrations of fire-resistance rated assemblies, the construction documents often lack sufficient detail. As with fire protection systems years ago, a fairly typical set of construction documents will indicate that all penetrations shall be properly protected and a generic specification section will mention applicable standards, allowable manufacturers, installation requirements and close-out documentation (if discussed at all). This practice has often led to unnecessary engineering judgments because the method by which the penetrations are to be protected was not fully considered by the design team.
In other instances, the details of the fire-resistance rated assemblies will be incomplete or reference incorrect material, such as an acoustical sealant where a fire-resistant joint system is required by the building code. Some construction documents will reference a tested wall assembly identified in a directory that does not provide the actual construction means and methods resulting in a contractor or code official needing to find the same assembly in a more comprehensive directory or obtain a copy of the test report.
While the IBC requires complete construction documents and fire protection system shop drawings, there is no similar language in the code that requires the same level of detail for passive fire protection features (see IBC-2021, 107.2.2).
Design professionals should prepare construction documents with the same standard of care as is used for active fire protection systems. Not only will this increase the likelihood that the construction is proper, it will also allow for more efficient enforcement by code officials and third-party entities.
More recent editions of the IBC have also addressed this issue by requiring special inspections for certain passive fire protection features for certain buildings, such as high-rise buildings. In addition, because current codes require that building owners maintain an inventory of all fire-resistance rated construction, proper construction documents will better enable owners to satisfy this requirement (see International Fire Code, 2021 edition; 701.6).
Many jurisdictions and some reference standards, such as NFPA 72: National Fire Alarm and Signaling Code, have qualifications for contractors who install active fire protection systems. It is less common to find technical qualifications specific to contractors who install passive fire protection features, unless they are contained in the project specifications.
As such, it is not uncommon for the general contractor to delegate the responsibility to various contractors. Not only can this lead to inconsistencies throughout the building, but it also can lead to the improper coordination between the various trades. These inconsistencies and the use of differing products and assemblies throughout the building add complexities to the inspection and maintenance activities required to be performed by building owners post occupancy.
With respect to lack of coordination, incomplete construction documents and inadequate acceptance and testing of passive and active fire protection features and systems can result in system failures. In December 2015, 25 people were killed and more than 100 people were injured in a hospital fire in Jazan, Saudi Arabia. The following were some of the factors that contributed to the outcome of the fire:
- Smoke barrier walls were not constructed to be continuous to the underside of the floor slab above. In addition, the doors in the smoke barriers were not capable of resisting the passage of smoke.
- Smoke detection was provided to actuate heating, ventilation and air conditioning system shutdown but the connection to the HVAC control equipment was not completed.
- Expanded plastic foam forms were left in place in the above ceiling plenum space.
Whereas all the fire deaths occurred remote from the area of origin, these three factors were significant and contributed to the fire and smoke spread in the plenum space above the ceiling. These three factors can be attributed to incomplete construction documents, inadequate acceptance testing or commissioning of building systems and inadequate oversight of the work performed by a subcontractor.
While the recent fire experience in hospitals in the U.S. has not resulted in multiple death fires such as the one in Jazan, that is partially due to the fact that hospitals in the U.S. have both active and passive fire protection features and systems. The hospital in Jazan was not protected with an automatic sprinkler system.
However, some of the same factors that contributed to the outcome of the fire in Jazan, including ones not listed above, have been found to occur in U.S. hospitals as well. For example, several years ago a client called indicating they had to evacuate a major portion of a new hospital. The client indicated that the fire occurred in a building adjacent to the hospital and that smoke entered the building through supply air vents and was then circulated throughout the building. It was determined later that the HVAC system shutdown was not properly installed, or commissioning was not completed adequately.
Another example of failures that can occur are changes that are made during construction that are not properly reviewed by the design professional in responsible charge or the code official. While not related to fire protection, the classic example of such a failure and one that is often used in professional ethics seminars, is the Hyatt Regency Kansas City walkway collapse in July 1981 that resulted in 114 deaths and 200 injuries. Factors that contributed to the collapse included:
- Inconsistencies between the design documents and the shop drawings.
- A change in the design of the suspending rod that was not verified.
- Inaccurate load calculations.
- Poor communication between interested parties.
With the exception of inaccurate load calculations, the wall installation shown in Figure 2 is the result of essentially the same factors. A change was made by the installing contractor resulting in a fire-resistance rated corridor wall being constructed differently than shown on the design drawings with poor communication between all interested parties. The design detail actually shows the drywall being continuous to about 0.5 inches from the deck and the space was to be filled with an acoustical sealant, not a fire-resistant joint system. The contractor changed the way the wall would be constructed to produce a more appealing finish.
As constructed, a portion of the joint between the floor slab and top of the drywall was filled with a fire-resistant joint system but not the gap between the fire-resistant joint system and the top of the drywall. Is this still a fire-resistance rated wall assembly? Was this reviewed by the design professional in responsible charge? Was this reviewed by the code official who reviewed and approved the project for construction? It should also be noted that the design profession and code official fulfill their responsibilities using periodic site visits and are not providing continuous oversight of the construction.
Inspection, testing and maintenance
Design documents should be reviewed by the person(s) responsible for inspecting, testing and maintaining the active fire protection system being designed. Design professionals should give equal consideration to the ongoing inspection, testing and maintenance of passive fire protection features and systems. Fire codes require periodic inspection of passive fire protection features and systems.
It is imperative that access be provided to perform the required inspections and test or features with remote inspection or testing capability be used. While the initial cost will be higher for remote test capability, the total cost of ownership will be reduced in many instances.
Passive fire protection features and systems in buildings are critical components impacting the overall level of fire and life safety being provided. In addition to making sure that active fire protection systems are properly designed, installed and maintained, the same level of care needs to be devoted to passive fire protection features and systems.
Design professionals should also consider if additional safeguards, whether active or passive, should be provided beyond minimum code requirements to meet the goals and objectives of the client. Remember that the services provided by engineers are to be dedicated to the protection of public health, safety and welfare.