Understanding NFPA 101 for mission critical facilities
- Understand the occupancy-type classification for data centers.
- Realize the differences in NFPA 101: Life Safety Code requirements for business and industrial occupancies.
- Explain critical life safety system requirements.
What does a data center and a laundromat have in common? As far as the International Building Code (IBC) is concerned, they are both considered "Group B Business Occupancies." As per IBC Section 304 Business Group B, both types of businesses have the same basic set of minimum requirements to safeguard the general health and welfare of occupants. Group B Business Occupancies are generically defined as occupancies that include office, professional, or service-type transactions including storage of records and accounts. Data centers and laundromats fall under the listed subset business uses of "electronic data processing" and "dry-cleaning and laundries: pickup and delivery stations and self-service," respectively.
Why does this matter? All building codes focus on ensuring the health and safety of a building’s occupants. The purpose of building codes does not include quantifying the inherent value of your dirty laundry versus data sitting on a computer server. What is considered "mission critical" by you and a client may not be shared by the authority having jurisdiction (AHJ). While there are certain exceptions, such as designated critical operations areas (DCOA) as defined by Article 708: Critical Operations Power Systems (COPS) of NFPA 70: National Electrical Code (NEC), code considerations typically don’t extend beyond the health and safety of a building’s occupants.
While the IBC is a far-reaching code encompassing structural, sanitation, lighting, ventilation, and several other areas, life safety considerations in mission critical environments is an important area of focus. The applicable code is NFPA 101: Life Safety Code, which has a more detailed perspective than IBC and is limited to life safety. Similar to the IBC, NFPA 101 is an occupancy-based code. NFPA 101 broadly categorizes occupancy types into the 12 following categories:
- Ambulatory health care
- Day care
- Detention and correctional
- Health care
- Residential board and care
The formal definitions for each of these categories can be found in Chapter 6.1 of NFPA 101. Each of these categories is characterized by the quantity and type of occupants, the type of hazards to which they may be exposed, and the factors that affect the ability to safely egress those occupants out the building in the event of a fire. Interestingly, unlike IBC, NFPA 101 does not define a specific occupancy type for data centers (or self-serve laundromats, for that matter). This does not mean that NFPA 101 does not apply to data centers. Remember that NFPA 101 is not a prescriptive cook book and requires a certain amount of interpretation to apply it properly.
Is a data center a business or an industrial occupancy?
There can be uncertainty regarding the occupancy-type classification for data centers. NFPA 101 defines an industrial occupancy as "an occupancy in which products are manufactured or in which processing, assembling, mixing, packaging, finishing, decorating, or repair operations are conducted." This broad definition would not seem to apply to data centers. However, "telephone exchanges," which also are defined as a Group B Business Occupancy under IBC, are instead specifically defined as an industrial occupancy type under the Annex Section A.188.8.131.52 of NFPA 101. While this annex material is intended to be informative and not part of the base requirements of NFPA 101, it is the most definitive interpretation that most AHJ’s will have immediate access to.
Historically, a telephone exchange consisted of numerous human operators manually connecting calls with telephone switchboards-similar to a modern call center. However, modern telephone exchanges/central offices are quite different from that historical definition and do not look much different from a typical data center (see Figure 1). So while the IBC makes a clear distinction between "telephone exchanges" and "electronic data processing," the basic functionality, occupancy, and characteristic hazards for these two different uses would seem to be similar in a modern context. By extension, it would be reasonable to assume that if NFPA 101 defined modern telephone exchanges as an industrial occupancy, that classification should also apply to mission critical data centers. Ultimately, that determination is at the discretion of the AHJ.
The primary question is why would there be a difference in a data center’s occupancy classification between the IBC and NFPA 101? Without a clear definition, it is debatable as to what a data center is per NFPA 101. Without such guidance, the primary consideration should be an assessment of what occupancy patterns and characteristic hazards are present in a data center environment. Mission critical data centers are characterized by:
- Unusually high power densities-can easily be more than 100 W/sq ft in the "white space" where the physical server equipment is located, necessitating top-of-row busduct and other similar electrical distribution equipment
- Onsite energy storage in the form of lead-acid batteries and diesel fuel, which can be fire hazards in of themselves when present in sufficient quantity
- Unusually high air movement/cooling requirements-can be more than 400 cfm/server cabinet in high-density environments
- Concealed/confined spaces (containerized data centers, raised floors, isolation of hot/cold aisles, etc.) (see Figure 3)
- The need for single-shot, total flooding clean agent fire suppression systems that require compartmentalization to function properly in lieu of traditional water-based fire suppression systems
- The need for redundant mechanical, electrical, and plumbing (MEP) infrastructure to ensure continuity of service
- A relatively low headcount as compared with traditional business occupancies, with the occupants often clustered in one particular portion of the facility
- The need to restrict access to the facility to only authorized personnel for security reasons.
Again, the purpose of NFPA 101 is to mitigate risks associated with safely evacuating the occupants of a building in the event of a fire. The primary consideration should be an analysis of "if" and "how" each of these factors impacts the NFPA 101’s ability to mitigate those risks, and based on that analysis, which occupancy type provides the most appropriate level of safety for the occupants.
While the generic definition of an industrial occupancy might not seem to be the most appropriate description for a data center, NFPA 101 also lists a "special purpose" industrial-occupancy subset that is described as an industrial occupancy in which ordinary and low-hazard industrial operations are conducted and characterized by a relatively low density of employee population, with much of the area occupied by machinery or equipment. This particular description might be a better fit for most data center environments where the white space and supporting mechanical, electrical, and similar unoccupied back-of-house rooms dominate the overall composition of a facility.
Although not incorporated as a reference standard in NFPA 101-2015, NFPA 76: Standard for the Fire Protection of Telecommunication Facilities supports this occupancy categorization. The special-purpose industrial-occupancy subset does allow a significant reduction in the egress requirements for a facility, but that ability to reduce life safety provisions and associated costs should not be the primary consideration when selecting this particular occupancy type. Before reducing life safety features, a risk analysis should be performed to confirm that this is the appropriate course of action.
In some cases, the data center might be incidental to the primary function of the building (i.e., a small server room in a commercial office building), which would allow it to be classified as part of the larger business occupancy. In other cases, it might be exactly the opposite (i.e., a network operations center within a large containerized data center). While incidental uses are discussed under NFPA 101’s "Multiple Occupancies" section 184.108.40.206.3, there is no prescriptive-area-ratio threshold in NFPA 101 to determine if a usage is "incidental."
The AHJ may, in some cases, classify the facility as a multiple-occupancy building (part business and part industrial occupancy) that necessitates a multiple-occupancy designation. In these cases, the most restrictive requirements would apply if no physical separation exists, as described by NFPA’s separated occupancy provisions.
Requirements for business, industrial occupancies
When reviewing NFPA 101, most engineers are surprised by how little content is devoted to the MEP systems that are specified. There are inherent limitations for all codes, but when considered as a group, they can be complementary and not compromise the overall intent of the code. NFPA 101 incorporates, by reference, numerous other pertinent NFPA codes and standards related to MEP systems.
Although many MEP systems such as sprinklers are only briefly mentioned in NFPA 101, their presence can directly impact seemingly unrelated provisions in NFPA 101. For example, the primary distinction between business and industrial occupancies is allowable travel distance. Many engineers may consider travel distance to be an architectural design issue. While NFPA 101 specifically does not require an NFPA 13: Standard for the Installation of Sprinkler Systems-compliant automatic fire sprinkler system in all types of business and industrial occupancies, it is recognized that sprinklers are the most effective means of preventing a fire from spreading. Accordingly, the maximum allowable travel distance is increased when they are present for both occupancy types. This can allow significantly greater flexibility for an architect in laying out a facility. Note that NFPA 101 makes a distinction between automatic fire sprinkler systems and "other automatic extinguishing equipment" such as gaseous fire suppression systems.
NFPA 101’s vague details on the life safety systems that are regularly specified by engineers can cause some confusion. NFPA 101 only mandates if a particular type of life safety system should be present within a given occupancy type. Although most of these systems are not discussed in-depth in NFPA 101, understand that when parts of other codes and standards are directly referenced in a particular section (for example, NFPA 2001: Standard on Clean Agent Fire Extinguishing Systems is referenced in NFPA 101 Chapter 9.8 "Other Automatic Extinguishing Equipment"), they should be considered integral to the requirements of that section.
If NFPA 101 identifies the requirement for a specific life safety system, the function of the referenced code or standard is to provide additional detail as to what is acceptable for the configuration and installation of that system. As such, any referenced codes or standards should be considered a legally enforced part of NFPA 101.
While potentially required by other building codes, NFPA 101 does not specifically mandate many of the engineered, life safety-related systems that are typically specified in a data center environment. Mission critical facility owners require emergency generators, clean agent fire suppression, early warning fire detection, and similar systems to minimize the chance of catastrophic damage or disruption to the normal operation of a very expensive asset. Although these types of elaborate systems may not be specifically mandated, when provided, they must meet all applicable provisions of NFPA 101. While the owner’s primary motivation for investing in these systems may be to ensure business continuity, the engineer’s ultimate responsibility is to properly apply the code as it pertains to these systems to ensure the safety of the building’s occupants.
The life safety systems that are typically the most important to electrical engineers are:
- Means-of-egress components
- Emergency lighting
- Fire detection and alarm
- Automatic sprinklers
- Other automatic extinguishing equipment.
The following commentary for each of these will often derive more from the referenced codes and standards than from NFPA 101. It also should be noted that while NFPA 75: Standard for the Fire Protection of Information Technology Equipment and NFPA 76 would seem to be very pertinent to any discussion of life safety within the data center environment, neither is directly incorporated as a reference standard into NFPA 101.
Means of egress
There are numerous tragic examples of obstructed paths of egress contributing to the loss of life during a fire. The 1927 Building Exits Code, which eventually evolved into NFPA 101, was in part developed in response to these types of tragedies. The code emphasizes the basic concept that the ability to survive a fire depends on the occupants’ ability to safely and quickly get out of the building. NFPA 101 requires a continuous and unobstructed path of egress from any accessible point in the building to the public way or a suitable exit discharge (Section 7.7.1). As such, doors must be easily opened from the egress side. All components of the means of egress must be "under the control" of the occupants.
There must be a balance between maintaining a secure environment and allowing safe egress during an emergency. Many data centers are equipped with security components, such as electromagnetic locking devices on doors, "mantrap" vestibules, and card-operated revolving doors, which may impede the free-egress requirement. While engineers are often not included in the initial architectural programming decisions that establish the need for such security components, the supporting life safety provisions typically fall under the engineering scope of work and, without proper coordination, can often fall through the cracks.
NFPA 101 uses specific terminology for egress door components that can’t be easily opened by turning a door lever or pushing a crash bar. This typically falls under the category of "special locking arrangements," and the subcategory is "access-controlled egress door assembly." This type of egress door is characterized by electric locking hardware and does not have a simple manual lever handle or push bar on the door leaf to allow for free egress. While acceptable for both industrial and business occupancy types per NFPA 101, certain requirements must be met:
- A sensor must be provided on the egress side to unlock the door upon detection of an approaching occupant (typically a passive infrared motion sensor above the door).
- The door must automatically unlock in the direction of egress upon loss of power (i.e., fail-safe).
- The door must be provided with a manual-release device ("push to exit" button or similar) within 60 in. of the door, and the door must remain unlocked for at least 30 seconds.
- The activation of the fire-protective signaling system automatically unlocks the door.
- Activation of the building’s fire detection or sprinkler system automatically unlocks the door.
- Emergency lighting is provided.
UL 294: Standard for Access Control System Units is also incorporated as a reference standard. As such, any approved hardware must be UL 294-compliant. UL 294 also includes a specific product category, FWAX, which pertains to "special locking arrangements" to prevent unauthorized egress. Activating a manual fire alarm pull station is not required by NFPA 101 to unlock these doors. However, this does not mean that the local AHJ will not require it. In fact, interpretation of egress-door hardware requirements can vary by jurisdiction, making it critical to confirm local requirements early in the design process.
For example, power-operated revolving doors with card access are often used in large data centers to minimize the chance of "piggybacking"-a situation where an unauthorized user could follow an authorized user into a secure facility. NFPA 101 has detailed provisions for use of revolving door assemblies as a component in a means of egress. The primary requirement is to have a breakaway leaf that freely and fully collapse into a book-fold position to allow free egress under similar conditions (power failure, sprinkler activation, etc.). However, even when such provisions are included with power-operated revolving doors, the local AHJ may require additional safeguards beyond what is required in the code or even prohibit their use altogether.
Using two-way security (i.e., card readers used to enter and leave) also is regularly forbidden by AHJs unless additional provisions, such as extra doors with delayed-egress hardware, are included. While local requirements can vary dramatically, any discussion with an AHJ on this subject should be predicated on the core goal of providing the most appropriate degree of safety for the building occupants, not what provides the greatest amount of security for the building’s contents.
It may be a controversial statement to say that emergency lighting is not required in special-purpose industrial occupancies without routine human habitation. While NFPA 101 states that emergency lighting must be provided for industrial occupancies in general, the first exception in 220.127.116.11(1) clearly states that emergency lighting is not required in special-purpose industrial occupancies. That is a statement of fact, but not always the appropriate engineering decision when trying to ensure life safety for the building’s occupants.
The primary function of emergency lighting is to provide adequate illumination for the path of egress out a building for its occupants. But what if the building is usually empty? While NFPA 101 recognizes that many special-purpose industrial occupancies are normally unoccupied, the engineer also has to consider the characteristic hazards in a data center environment and determine if omitting emergency lighting from usually unoccupied buildings impacts the safety of the occupants who may infrequently work within the space (security, maintenance staff, etc.). This question becomes more pertinent in contained data centers (i.e., a "plug-and-play" data center in an intermodal shipping container) that have high densities of equipment and supporting infrastructure in an unusually confined environment. This decision to provide emergency lighting becomes moot if any type of access-controlled egress-door assembly is provided, which separately mandates emergency lighting elsewhere in the NFPA 101.
Even if not directly required by the AHJ or NFPA 101, the potential hazards often justify the inclusion of emergency lighting-even if the area is rarely occupied. Although not mentioned in NFPA 101, it should be noted that many AHJs will require emergency lighting if, in their determination, the safety of first responders will also be impacted.
Once the need is established, the actual illumination requirements for emergency lighting in NFPA 101 are relatively straightforward. Emergency lighting must provide initial illumination so that at least an average of 1 fc (10.8 lux) and a minimum of 0.1 fc (1.1 lux) is maintained along the path of egress at floor level. It is allowable for these levels to decline to not less than an average of 0.6 fc (6.5 lux) and a minimum of 0.06 fc (0.65 lux) at the end of 90 minutes. To maintain a reasonable amount of uniformity, the maximum-to-minimum illumination cannot exceed a 40:1 ratio.
Approved auxiliary sources
Beyond a statement that emergency illumination must be maintained for 90 minutes in the event of a failure of normal lighting, NFPA 101 is fairly vague regarding the configuration and installation requirements for auxiliary power source requirements serving emergency lighting. Most of the details fall to the referenced codes and standards NFPA 70, NFPA 110: Standard for Emergency and Standby Power Systems, and UL 924: Standard for Emergency Lighting and Power Equipment. NFPA 101 does, however, specifically mention that emergency power systems need to be compliant with NFPA 110, Type 10, Class 1.5, Level 1 emergency power system requirements (see Figure 4). Level 1 is the most stringent and is used "where failure of the equipment to perform could result in the loss of human life or serious injuries." These systems have the following basic requirements:
- Must restore power within 10 seconds of the primary source
- Must be able to support the load without being refueled for at least 1.5 hours
- Have an enhanced/expanded set of monitoring and alarm functions.
Again, the referenced codes and standards should be considered an integral part of NFPA 101 in the context of the sections in which they’re mentioned. When any particular type of system is provided, even if not required by NFPA 101, it has to meet the applicable reference code. Certain standby systems that are characteristic of large data centers, such as large multimodule uninterruptible power supply (UPS) units and paralleled generator systems, may seem to meet the fundamental requirements for emergency lighting auxiliary sources. When considered in the context of the other codes and standards, there are small details that may make an otherwise highly resilient backup system technically inadequate for emergency lighting use.
Use of a data center’s UPS system for emergency lighting should be avoided. Although NFPA 76 does have provisions for using a telecommunication facility’s battery system to power the emergency lighting, this very broad statement can be misleading and discounts conflicting requirements in other codes and standards. The first hurdle is that any UPS used for emergency lighting must be listed for central-lighting inverter duty in accordance with UL 924. This listing is extremely unusual in larger-capacity UPS systems and nonexistent in multi-module UPS systems. Even if appropriately listed, optional standby loads still have to be segregated from emergency lighting loads in accordance with NEC Article 700.10. Even the requirements for an "emergency power off" (EPO) button can add further complications. The requirement for separation, and the prioritization of life safety loads over optional standby loads, would compromise the primary function of the UPS system to support data center equipment.
There are many considerations when evaluating a data center’s generator system to use as an auxiliary source for life safety systems. Most challenges revolve around the 10-second load-acceptance requirement in NFPA 110. While generator-paralleling control systems have evolved dramatically over the past few years, there are still concerns regarding the use of large, paralleled generator systems for life safety loads. Larger prime movers (about 2 MW and greater), which are becoming relatively common for large data centers, may not start as quickly as smaller generators. When considered in combination with the associated supervisory control and data acquisition (SCADA) system used to parallel generators and associated signal latency issues in larger control systems, meeting the 10-second threshold can sometimes be a challenge. Where U.S. Environmental Protection Agency Tier 4 emission packages are required (typically when generators are used for storm avoidance and rate curtailment), they can also add unexpected points of failure.
For example, failure of the generator’s emission system will usually cause an automatic shutdown of the generator system. The cause for the failure may be relatively benign, such as depletion of diesel exhaust fluid in the selective catalytic reduction (SCR) portion of the emissions system, and wouldn’t necessarily cause damage to the generator or otherwise affect its ability to generate power. However benign the cause may be, the fact remains that the ability to support the life safety load would be compromised. A separate, smaller emergency generator dedicated to life safety loads may be the better solution this challenge. Although inelegant from a design perspective, simple unit battery lights and exit signs with battery backup may also be compelling as a simple solution to an otherwise complex problem.
Fire detection and notification
While certain systems may not be mandated by NFPA 101 as part of the basic requirements for particular occupancy types, the presence of other seemingly unrelated systems can trigger installation. Fire alarm systems are no different. If other contributing factors are dismissed, the basic threshold for fire alarm systems is an occupant load of 100 people in an industrial occupancy and 1,000 people in a business occupancy. There are other factors that can significantly reduce these numbers depending on the height of the building or the proximity of the occupants to the primary level of discharge.
However, if-for example-a data center does not meet these reduced, minimum thresholds for a fire alarm system, the next question would be what characteristic hazards or other project owner requirements would necessitate the installation of a fire alarm system?
The most common project requirement that would trigger the need for a fire alarm system is installing a large UPS system. NFPA 1: The Fire Code and the International Fire Code both require the installation of smoke detection when the volume of electrolytes stored in the batteries reaches a certain threshold, typically 50 or 100 gal depending on which of these two codes is being followed. This requirement applies to the valve-regulated lead-acid (VRLA) batteries that are typically used in UPS systems, not just traditional wet-cell batteries. It is not unusual to exceed this threshold with as little as 10 minutes of battery capacity for a 160-kVA UPS.
Fire suppression systems
Although automatic sprinkler and similar fire suppression systems are often required by the AHJ, they are not mandated by NFPA 101 as part of the basic requirements for business and industrial occupancies. However, as previously stated, their presence allows for a certain leniency elsewhere in NFPA 101, such as longer paths of egress. Other codes and standards like those that apply to common data center installations, such as diesel-fuel storage and battery-storage battery rooms, may indirectly necessitate the installation of a sprinkler system.
Regardless, clean agent fire suppression systems that are not required by code are still commonly used to protect the server equipment within the white space. While not required, if a clean agent fire system is provided, it has to be furnished and installed in accordance with the applicable codes and standards. NFPA 2001: Standard on Clean Agent Fire Extinguishing Systems specifically requires automatic detection and actuation by default and requires a fire alarm system for proper operation and supervision.
-John Yoon is a lead electrical engineer at McGuire Engineers Inc. and is a member of the Consulting-Specifying Engineer editorial advisory board.