Part two of this three-article series takes a look into the use of elevator shunt trips in fire emergencies.
by Dan Winslow, CEIS
History Summary
From the timeline published in Part 1 of this series, we can make the following generalizations:
- Shunt trip in the A17.1 elevator code is intended to prevent movement of the elevator in any circumstance where a fire sprinkler operation could affect the movement of an elevator.
- Protection of elevator control using shunt trip is not related to elevator fire service, building height or elevator type.
- Elevator control does not include auxiliary systems such as cab lighting, communication equipment or other non-elevator electrical equipment located in hoistway, machine room or pit.
- Protection of the elevator control includes any elevator equipment located in the hoistway, control spaces, machine spaces and pit where water from sprinklers could cause unsafe operation.
- Although desirable, shunt trip is not dependent on completing recall, and it is recognized that the elevator shunt trip could entrap passengers.
- Fire-alarm systems used to initiate shunt trip are not permitted to use the elevator control system as a means to verify that recall has been completed.
- The elevator code requirement that states that sprinklers “shall be permitted to be installed” has not changed since its adoption in the ASME A17.1-1994a edition and prior to 1994, the provision for sprinklers in the hoistway goes back at least 55 years to the ASME A17.1-1955 edition.
Frequently Asked Questions
- Question: Is Fire Service required when shunt trip is provided?
No, the two are completely independent, and conversely, shunt trip is not required when fire service is provided. While desirable to recall the elevators prior to disconnecting power, shunt trip may trap passengers. - Question: Can the fire-alarm system be arranged to delay shunt trip until the elevator recalls?
Answer: No. Because the elevator control system is not permitted to initiate a signal to the fire-alarm control unit (FACU) verifying that recall has occurred, any predetermined delay must operate independent of recall operation. Therefore, although the fire-alarm system itself may have the capability of a delay, since there is no approved means for the FACU to be notified that the elevator has completed recall, the FACU cannot be permitted to delay until recall has been confirmed. - Question: Can a sprinkler preaction system be arranged to prevent water flow from sprinklers until the elevator recalls?
Answer: No. Although the preaction system may have capability to delay application of water, there is no means to notify the releasing means that the elevator has actually been recalled. Sprinkler system design assumes control of a fire at its source with as few sprinklers as necessary. By maximizing the volume of water and delivering it to as small of an area as possible (water density = volume over area), the system applies as much water as quickly as possible (flow rate) to as small an area as possible to prevent the spread of the fire beyond the capabilities of the water supply to control it. Where sprinkler operation is permitted to be delayed, such as with a dry pipe system, system designers must increase the water supply density by designing for more water volume over a larger area. However, even this method only provides a short time delay (generally 60 seconds). Since a preaction system cannot receive verification from the FACU that recall has completed, it must be arranged with a fail-safe timer and provided with additional water supply. (An example of a preaction system specifically designed for use in elevator machine rooms is manufactured by Fire Flex.) - Question: Where a time delay is used, is it sufficient to determine the length of time delay by measuring the time it takes the elevator to travel from its furthest vertical point to the furthest recall location?
Answer: No. The speed of the elevator over the travel distance of the hoistway does not take into account the real possibility that an elevator may be at a landing with the doors open at the time recall is initiated. Where the elevator is stopped at a landing, the time to close the doors, plus the potential that door closing time could be delayed by a passenger holding the doors open could cause a delay significantly longer than a simple time/distance calculation. Where time delays are provided, they must always assume a false safe limit based on the limitations of the sprinklers to control a fire after a delay. - Question: Is shunt trip permitted if sprinklers are not present in the machine room or hoistway?
Answer: Yes. There is nothing that requires or prohibits shunt trip if sprinklers are not present. Understanding that the temperature at the ceiling that initiates a sprinkler water flow would be a minimum of 79ºC (175ºF) and that a typical modern elevator controller (which is really just a computer) is only rated by the manufacturer for safe operation below about 43ºC (110ºF) it would seem to be necessary to shunt trip whether a sprinkler is present, since the elevator controls would no longer be expected to operate safely. - Question: Are there other devices besides heat detectors that are permitted to initiate shunt trip?
Answer: Yes, if the device is approved for use as a fire-alarm initiating device (FAID), and as long it is not a smoke detector. Although using heat detectors are the most common method, flow switches are also widely used. NFPA 72, Section 6.15.4.3 notes that where flow switches are used, they are not permitted to have a time delay, because by its nature, waterflow has already taken place. The advantage in a flow switch is that there is no potential of an accidental shunt trip due to delayed or premature activation by a heat detector or where a sprinkler is broken. Where flow switches are used, a check valve on the supply side of the machine room/hoistway sprinkler line is generally recommended to reduce the potential of an accidental shunt trip due to water surges. Note that because a method to test flow switches is also required, the test port discharge location should be carefully considered. - Question: Is a heat detector used for shunt trip required to be within 600 mm (2 ft.) of each sprinkler head located in the elevator machine room or hoistway?
Answer: No. NFPA 72, Section 6.15.4.2 provides alternative spacing using engineered spacing methods. Although the 600-mm (2-ft.) rule is the common method, it can be prohibitively expensive and possibly unnecessary when there are several sprinklers located in a medium-sized machine room. In larger machine rooms, a flow switch is likely more economical than either heat-detector spacing methods. - Question: Is a sprinkler required in the pit of a hydraulic elevator if there are no combustible hydraulic fluids?
Answer: No, although the exception exists in NFPA-13, Section 8.14.5.2, NFPA 220 Standards on Types
of Building Construction defines “non-combustible” as materials that pass the ASTM E136 Standard Test Method for Behavior of Materials in a Vertical Tube Furnace at 750ºC (1300ºF). Since typical 150 Grade 68 Hydraulic Fluid has a flash point of only 220ºC (430ºF), the exception doesn’t apply to hydraulic fluid. Another typical question regarding this exception is whether an oil buffer would require a sprinkler in the pit. Since oil buffers are normally sealed vessels and wouldn’t typically have oil exposed to a source of ignition like typical hydraulic cylinders with wiper rings would, they shouldn’t present a significant fire hazard and wouldn’t likely require a sprinkler in the pit. - Question: Where a sprinkler is provided in the pit, is a smoke detector (or heat detector) required in the hoistway?
Answer: Undetermined. NFPA-72 section prohibits the use of a smoke detector in hoistways unless there are sprinklers present or they are required to operate a smoke management vent. From a literal point of view of the requirement, it would seem that a smoke detector would be required in the hoistway even if a sprinkler is only installed in the pit, because the pit is considered by A17.1/B44 to be part of the hoistway. However, it may not be practical to locate a smoke detector in the hoistway solely for a sprinkler in the pit, because smoke typically moves vertically away from the source of heat. A smoke detector in the pit may not activate if the upward movement of the smoke from a pit fire fails to initiate a signal, and a detector installed at the top of the hoistway would likely be arranged to initiate a signal to move the car down, toward the pit fire. In fact, this problem can occur in any scenario where a fire is located in the pit, because smoke detectors are only designed to be installed on smooth, flat ceilings and never intended for installation in the hoistway environment. The option to use a heat detector could be considered for recall if approved by the AHJ (See NFPA-72, Section 21.3.7); however, it should be understood that smoke and heat detectors should not be considered interchangeable, in terms of their intended function. - Question: Is it acceptable to simply install a solenoid-operated valve in-line with the supply side of the machine room/hoistway arranged to open the sprinkler pipe?
Answer: No. A solenoid-operated water valve cannot be installed as a standalone fire-sprinkler control valve. Although solenoid valves are widely used in the U.S. and Canada as components within a preaction system for fire protection, the valves are not agency listed as standalone products for fire protection. NFPA-13, Section 6.1.1 requires that solenoid valves in a fire sprinkler system be listed for their specific use, and NFPA-72, Section 10.3.3 requires that all components receiving their power from an initiating circuit be listed for use with the FACU. A standalone solenoid valve may not meet the standard for a listed releasing service. - Question: Is it acceptable to install the shunt trip means at a location other than the mainline disconnect in the machine room?
Answer: No. NFPA 70 620.51(c) requires the disconnecting means to be located “within sight of the motor controller”, and NFPA 70 620.51 (B) requires that “no provision be made to open or close the disconnecting means from any other part of the premises.” Because the elevator mainline disconnect is the disconnect means, the shunt-trip means must also be at the elevator disconnect location. - Question: Is the visual signal (flashing fireman’s hat) required by ASME A17.1/B44 Requirement 2.27.4.2 required to flash after shunt trip has been initiated?
Answer: No. Although a FAID in the machine room could serve as warning signal to emergency personnel that the elevator control may be compromised by a fire in the machine room or hoistway, once shunt trip has taken place, the point is moot. Since the shunt-trip means is required to be reset manually
at the location of the disconnecting means in the machine room, the elevator wouldn’t be available until emergency personnel verified the tenability of the elevator equipment, anyway. If the emergency personnel determine that the machine room/hoistway are safe for elevator operation, the circuit breaker can then be reset.
Shunt Trip in the 21st Century and Beyond
Consolidation and coordination of the model codes has been the hallmark of the consensus method of code writing for decades. Working together to bring about a robust open dialogue among stakeholders has been the surest way to ensure a safer building environment. Examples of this have been the consolidation of the U.S. and Canadian elevator codes into a single document and the coordination between ASME and NFPA regarding shunt trip and fire service. NFPA 72-2007 Handbook Supplement 2 states, “There is now a spirit of willingness and cooperation between industry, code enforcement, and the fire service to continue to work together to find the best solutions to achieve the highest level of safety and reliability for passengers and emergency personnel who use the elevators.”
Going forward, we must remember that elevators do not exist on an island unto themselves. Elevators are just one component of a complicated building technology intended to serve people, not the other way around. The following are some key points that all stakeholders must keep in mind regarding shunt trip.
- First and foremost, the intent is to remove power from the elevator controls whenever there is the potential that the elevator operation is unsafe.
- The reason that the sprinkler is in the machine room/hoistway is to control a fire that has already started. We spend hours every day in offices, hospitals, malls and factories without ever thinking about the hundreds of sprinklers over our heads, because fire sprinklers do not go off randomly. In elevator machine rooms and hoistways, they go off because either the elevator equipment or surrounding storage is on fire. In either case, the danger posed to passengers stuck in an elevator after shunt trip is significantly less than that to those riding on an elevator on fire. Further, since all of the major elevator manufacturers require the elevator machine room to be maintained at a maximum of about 43ºC (110ºF) for safe operation, it should be universally agreed that if it’s hot enough at the ceiling for a sprinkler to operate, the elevator equipment is already operating “unsafely.”
- Where practicable, every effort must be extended to remove passengers from the elevator prior to shunt trip. However, it has always been understood that it is less onerous to trap passengers in an elevator than to allow the elevator to move if the controls have been compromised, either by water or by heat.
- The 2009 edition of the International Building Code, the standard for most of the U.S. includes extensive new standards for elevators with the addition of two new types of elevators generically called “Occupant Egress” and “Fire Service Access” elevators. While the National Building Code of Canada has tabled any changes to its building code pending model code coordination, the Inuit Circumpolar Council (ICC) has moved ahead of the coordination process. Currently, these types of elevators don’t even exist in the A17.1/ B44-2009 edition. The results of a hazard analysis by the ASME A17 Task Force on Elevator Fire Emergencies was presented on December 1-2, 2010, at the “Symposium on the Use of Elevators in Emergencies in High Rise Buildings.” (For additional information, visit website: http://events.asme.org/elevatorsymposium10.) Expert presenters discussed some of the general concepts behind “Occupant Evacuation” and “Fire Service Access” elevators. However, it may yet be premature for stakeholders to consider these new types of elevators until the reference standards by which they are to be built can digest the obstacles they present to the built environment.
- As it relates to this article, the presumption of the IBC-2009 regarding shunt trip is to include a new exception for “occupant egress elevators” in Section 3008.6.1 prohibiting sprinklers in elevator machine rooms, and in Section 3008.8 prohibiting shunt trip entirely. The exception to NFPA-13, Section 8.15.5.3 only applies to this new type of elevator in some very tall buildings, which appears to be intended to operate in extreme emergency conditions to evacuate building occupants and may allow for elimination of a required additional exit stairway. (See IBC-2009, Section 405.3.2. exception for buildings 128 m or 420 ft. in height.) It should also be noted that it is anticipated that in a future IBC edition, “Fire Service Access” elevators, apparently specifically intended for use by firefighters during fire emergencies would also be exempted from both the sprinklers and shunt-trip requirements.
- As stated in the NFPA-13 2011 handbook, Section 8.15.5 editorial regarding considerations to remove sprinklers from machine rooms “ . . . omission of sprinklers by local officials needs to be carefully considered, due to the possibility of uncontrolled fire growth combined with simultaneous fire department dependence on the elevators. Additional concern surrounds the fire department’s assumption when responding to a fire incident in a machine room that such spaces within the building are fully sprinklered.” This makes it doubly surprising that NFPA-101 2009 also adds new “Annex B” material that includes “occupant controlled evacuation” elevators. Although annex materials are not considered part of the National Fire Protection Association (NFPA) code requirements, Section B.4.2 does include an exemption for sprinklers in machine rooms. Interestingly, it adds a rationale recognizing that the exception conflicts with NFPA-13. NFPA-13 provides no reference to “elevators used for evacuation,” and although NFPA-72, Section 21.6 does reference “elevators for evacuation,” there are currently no specific references to shunt trip.
- According to NFPA 101 rationale, elevator machine rooms are similar to “electrical rooms,” and since there is an exception for electrical rooms, according to the commentary, elevators should also be allowed to utilize the electrical-room exception. While it’s true that elevators have equipment that may appear to the similar to that found in electrical rooms, it should be obvious that electric rooms are not used to transport people while on fire, either. Additionally, Annex B.5.2, parroting the ICC exception, also prohibits shunt trip, rationalizing that sprinklers aren’t present, and therefore, shunt trip isn’t necessary. That would make sense if the elevator equipment getting wet were a more serious risk to passengers than if it were burning.
The exception for “occupant controlled evacuation” elevators also contradicts 25 years of ASME A17 shunt-trip rationales by prohibiting the elevator controls from shutting down if the machine room exceeds the safe operating temperature apparently in violation of ASME A17.1/B44 requirement 2.7.9.2 requiring the machine room to be maintained per manufacturer’s specifications. It’s highly unlikely that the machine-room air-conditioning was designed to keep the temperature under control, while the room or elevator is on fire. It could be interpreted that even if you could guarantee the elevator had recalled and you knew the machine room was on fire, you would still not be permitted to disconnect power to the elevator by means of shunt trip.
In Part 3 of this series, we will provide the perspective of shunt trip from Canada, provide definitions of various terms related to this subject and offer a conclusion to the discussion of this important topic.
Reference Standards
Unless otherwise stated, the following reference standards are used in this article:
- American Society of Mechanical Engineers (ASME) A17.1/B44-2009b: American Society of Mechanical Engineers A17.1 Safety Code for Elevators and Escalators (www.asme.org)
- National Building Code of Canada
- International Code Council (www.iccsafe.org)
- International Building Code 2009
- National Fire Protection Association (www.nfpa.org)
- NFPA 13: National Fire Protection Association Automatic Sprinkler Systems 2010
- NFPA 70: National Fire Protection Association National Electric Code 2011
- NFPA 72: National Fire Protection Association National Fire Alarm Code 2010
Acknowledgements
The author wishes to acknowledge the following individuals who contributed to these articles:
- Bruce Fraser, Fraser-Fire Protection Services
- Richard Roux, NFPA
- Mark Tevyaw, CET, CEIS
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