For those of us who have been engineering and specifying fire protection systems for 10 years or more, it would be safe to say, “You’ve seen one parking garage, you’ve seen them all.” The biggest and usually the only question ever asked about them is, “Are they open or closed?” 

Until recently, the major building codes prescribed fire protection for this S2 occupancy based on a percentage of the exterior wall open to the outside. If it is considered open, then generally a standpipe system was all that was required, and even that was based on square footage and number of stories. 

However, social media videos are popping up, showing major fires in parking garages, suggesting a fire problem there. And while this cannot be ignored, such as anything off social media, it should always be taken in context. Are parking garages burning? Has the hazard(s) changed? I think it’s safe to say that perhaps we should look at this occupancy again and see what we may be missing.

The major hazard for a parking garage is the vehicles parked in it. As mentioned, this used to be a typical singular target; not anymore. Today, we have internal combustion engines (ICE), hybrid (HB) and electric vehicles (EV). Other features that could contribute are EV charging stations at dedicated spaces or scattered throughout, depending on the garage layout. 

While we can argue about the occupancy classification being S1 or S2, it is clear we need to re-evaluate or perform a fire hazard analysis for this occupancy and see if current prescriptive solutions are still adequate. 

Of the three types of vehicles that may be allowed to park in a garage, HBs and EVs introduce the presence of lithium batteries (Li-ion). Including these vehicle types in the population changes the historical dynamics of the hazard for this occupancy type. 

EV Vs. ICE

NFPA 88A is the standard for parking structures and is considered the occupancy standard. It governs features such as means of egress, construction, building services (mechanical, electrical and plumbing) and fire protection. NFPA 88A-6.4.1 references NFPA 13 for the fire sprinkler criteria. From NFPA 13, the current prescriptive design criteria for this type of occupancy can be summarized as shown in Table 1.

This criterion has been in place for decades and, up until recently, has provided acceptable levels of protection as deemed necessary by the NFPA 13 technical committee. However, as mentioned, over the past several years, the materials used in vehicle manufacturing have changed significantly. 

Specifically, the materials used for a vehicle’s exterior body and the gas tank incorporate significant amounts of plastic. It is estimated that 72% of the North American vehicle market and almost 50% worldwide have switched to plastic gas tanks. The majority of these tanks are made from high-density polyethylene, or HDPE.

Another change in this occupancy is the addition of HBs and EVs to the parking population. The perceived concern with these vehicles is focused on the Li-ion batteries they run on. However, contrary to this perception, while the burning characteristics differ, the heat release rate (HRR) and frequency of conflagrations increasing is false. 

As noted in the recent study published by the National Fire Protection Research Foundation, “Modern Vehicle Hazards in Parking Structures and Vehicle Carriers,” (Boehmer, Klassen, Olenick, July 2020, pg. 30), the HRR of non-ICE vehicles is congruent with ICE vehicles (see Figure 3). 

Furthermore, the perception that more fires in parking garages result from introducing HBs and EVs into the parking population is false. Opinions about charging stations have permeated the conversation, asserting HB and EV contributions to the hazard, which does not have conclusive evidence either. 

Several studies point to a damaged battery as the root cause or existing condition, creating a thermal imbalance. The damaged battery overheats when charging begins, creating a thermal runaway. Nevertheless, most fires in parking garages that are started or involve vehicles are predominately ICE vehicles. 

These similarities should not minimize concerns raised with a higher HRR than in the past when the typical ICE vehicles had steel gas tanks and bodies. Nor should we neglect the presence of a new ignition source in the form of Li-ion batteries. Here, too, are misconceptions due predominately to social media. It is true an EV battery fire can be more dramatic and appears to be more like a jet or flash-type fire than a gasoline pool fire, but the fact remains that the HRR is similar to ICE. 

However, the significant difference between EV vehicle fires and ICE fires is duration. An EV fire can burn for hours compared to an ICE event that can be controlled and extinguished within minutes. It is called thermal runaway; once an EV battery package is ignited, there is only a small chance it can be controlled or extinguished, no matter how much water you discharge on it. Reports of EV fires say that tens of thousands of gallons have taken several hours to extinguish. Quite frankly, rarely are they extinguished, but rather burn themselves out.

Fire Protection Goals

So, we have a hazard that, in most cases, will burn at a higher HRR than in the past, given the materials involved, and has multiple ignition sources rather than the historical ignitable fluid. Using this information, several conclusions can be made supporting alternative design criteria for fire protection systems. This data can be converted to fire protection goals. 

For example, one approach toward this new challenge would look like this: We know we have higher HRR. Given this occupancy is sporadically occupied in public and private conditions, life safety comes first. Parking garage structures rarely have protected structural components; they are exposed. Hence, goal No. 1 should be the structure’s protection to maintain integrity throughout the fire event. 

Remember that typical parking structures do not have ceilings much more than 9 to 11 feet. This low ceiling height means heat collects and travels horizontally much faster, depending on the type or configuration of the structural components. This translates to features promoting early detection or increased sensitivity levels for sprinkler activation. This early suppression promotes adequate cooling at the ceiling level to support the structural integrity necessary for public evacuation and firefighting operations. 

Goal No. 2 is to provide adequate exposure protection, limiting the size of the event and how many vehicles may be involved. Today, there are various opinions on what would define success. The historical sprinkler criteria would suggest we could have as much as 1,500 square feet of vehicles involved at one time. If the average square foot area of a parking space is approximately 200 square feet, the typical sprinkler system would be protecting an area equal to 7.5 vehicles. 

Recent parking garage fires have shown that having more than two or three creates a serious challenge to not only the sprinkler system but to firefighting efforts as well. Exposure protection comes from cooling and pre-wetting adjacent surfaces or hazards. Recent modeling suggests that success should be no more than two vehicles involved. By adequately addressing these two goals, we could expect a two-car event to be attainable.

This two-goal philosophy is summarized in Table 2.

Active and Passive Systems

As mentioned, data does not support that a higher density would provide higher levels of protection; rather, ensuring adequate duration, given the presence of HBs and EVs, would be prudent. This would ensure that fire department operations could support and extend the exposure protection during the course of an EV battery fire. 

In response to Goal No. 1, several features would be included. First, quick-response sprinklers would be required. Sprinkler spacing would still be maintained at a maximum of 130 square feet/sprinkler; however, the maximum sprinkler spacing would be reduced from 15 feet to 12 feet. By adding this limitation, the maximum distance a sprinkler could be off a wall would be 6 feet, ensuring that at least two rows of sprinklers or branch lines would run over the top of the parking spaces. 

By closing up the sprinkler spacing, we effectively increase sensitivity. This improves our efforts toward early activation and results in cooling and exposure protection critical to successful control. The balance of the criteria would follow the historical guidelines that have proven effective.

A good fire protection program includes active and passive systems, and 21st-century parking garages are no different. While the fire sprinkler system addresses the active requirements, passive systems and design features are required to comprehensively respond to the new challenges of this old occupancy. 

Besides cooling provided by the sprinkler system, the parking garage layout can be manipulated using dedicated parking spaces with charging stations for HBs/EVs. These spaces can be located at the ends of parking rows, creating a single or one-sided exposure in lieu of allowing them to be “nested” in the middle of a row where vehicles are on both sides. 

Another important design feature focused on fire department operations would be clearance between rows and on the ends of rows where the turn radius is limited due to vehicle size and one-way or two-way traffic is allowed. Providing adequate clearance gives fire department operations the room to bring tow trucks or apparatus capable of pulling the vehicle out of its space into the middle aisle while it is burning, effectively removing it from adjacent vehicles while it burns through the fuel load.

Equally important to the success of the active systems is adequate signage and enforcement thereof. Prior to entering the parking garage, clear and visible signs alerting drivers of the dedicated spaces for HBs and EVs, along with rules and requirements for charging stations, should be posted before entering the garage. Enforcement should be mandatory and included in the ongoing inspection, testing and maintenance of other active and passive systems over the life of the occupancy.

Certainly, this is a snapshot of what traditional brick-and-mortar parking garage protection should consider, given the new vehicle types being manufactured. We have only begun to see the various configurations of mechanical and robotic garage systems showing up worldwide, introducing even more consideration for adequate levels of protection. 

For those engineers who have chosen to practice in the discipline of fire protection engineering, take note. Recognize that technology travels much faster than prescriptive codes and standards. Do your homework and make sure you have adequately addressed these new hazards and the building or systems being parked in. Always keep firefighting operations in the design. 

And by all means, keep your eyes on NFPA 88A through this current cycle. Significant proposals have been submitted that will influence how we move forward from here.

Steven Scandaliato is principal and managing director at SDG. He has more than 39 years of experience in fire protection engineering, contracting, design and project management, covering all types of fire protection and life safety systems. Scandaliato is a member of several NFPA committees, including 11, 13, 16, 101, 102 and 5000. He also serves on several technical committees, including the Technical Advisory Committee for the American Fire Sprinkler Association and the Society of Fire Protection Engineers.