NFPA 13 performance-based design solutions

Performance-based design insights

• Prescriptive and performance-based design of fire and life safety systems have practical applications, depending on a building’s use.
• Additionally, both designs have benefits and drawbacks to keep in mind when determining which type to implement.

All building and fire protection system designs must adhere to a set of criteria that are specific to the goals and objectives of a project. There are multiple NFPA committees that revise prescriptive codes and standards, like NFPA 13: Standard for the Installation of Sprinkler Systems, every few years.

In fact, there are currently five technical committees focused just on NFPA 13. The revisions to the codes and standards reflect advancements in industry knowledge and lessons learned from real-world fire events.

For example, the Station Nightclub Fire of 2003 prompted the National Institute of Standards and Technology to recommend a revision to model code that all existing nightclubs with an occupancy of over 100 people must be retrofitted with a sprinkler system and all new nightclubs must be built with a sprinkler system. Over the decades, dozens of fire events have contributed to the criteria of prescriptive fire codes, at the cost of life and property.

NFPA 13 states that “Nothing in this standard is intended to prevent the use of systems, methods or devices of equivalent or superior quality, strength, fire resistance, effectiveness, durability and safety over those prescribed by in this standard.”

This guidance has been in the standard since the 1983 edition was issued. It continues to state that technical documentation proving equivalency shall be submitted to the authority having jurisdiction (AHJ) that approves the use of performance-based design. Furthermore, NFPA 13 section 1.7 allows for new technology and alternate arrangements as long as the level of safety is not lowered. This section is very important as it shows that NFPA recognizes that there are multiple ways of achieving life and property protection, so long as the highest level of safety is maintained.

Figure 1: By quantifying the occupancy and commodity type, fire protection engineers can identify a potential fire scenario and determine what sprinkler design components will be necessary. Courtesy: Telgian Engineering & Consulting LLC

Prescriptive criteria

Examples of prescriptive criteria included in recent editions of NFPA 13 include:

• ESFR Sprinklers for Palletized, Solid-Piled or Rack Storage of Class I Through Class IV and Group A Plastic Commodities.
• Protection of Exposed Expanded Group A Plastics.
• General Requirements for Ceiling and In-Rack Sprinklers Protecting Rack Storage.
• Control Mode Density/Area Sprinkler Protection Criteria for Palletized, Solid-Piled, Bin Box, Shelf or Back-to-Back Shelf Storage of Class I Through Class IV Commodities.

The standard is full of criteria for several different water-based suppression applications, varying building uses and commodity arrays. Selection of the appropriate criteria requires the design professional to obtain specific knowledge of many items, including but not limited to: commodity classification and volume, storage layout, interior finish types, aisle widths and ceiling heights.

A significant limitation of prescriptive criteria is that it requires the facilities to be built and operated within the very specific requirements enforced by NFPA 13. This includes operational factors such as fixture types, product types, storage methods, aisles, storage and ceiling heights, etc. That way, the associated design densities, water flows, sprinkler and pipe sizes and pipe and sprinkler arrangements of the sprinkler system are effective.

If one variable is not within the intent of the regulations of the criteria listed in the standard, then other options, prescriptive or performance-based, must be researched.

Figure 2: A vital component to solving fire protection challenges, full-scale fire testing examines difficult to protect commodities, storage or display arrangements and rack configurations. Courtesy: Telgian Engineering & Consulting LLC

Performance-based design

Performance-based approaches date back to the 1970s when the United States General Service Administration developed goal-oriented approaches to building fire safety. In 1985, British Regulations published a performance-based document. Following Britain over the next 10 years, New Zealand, Australia, Japan and the Nordic Region all published their own performance-based design documents.

Later, NFPA 101: Life Safety Code was amended to allow for performance-based equivalencies in 2000 and the United States International Code Council amended International Building Code to include a performance option in the year 2003.

Performance-based suppression criteria are based on goals and objectives identified by the stakeholders of a project. These goals give the stakeholders specific objectives that must be met for an acceptable outcome. Examples might include:

Atmospheric temperature

If the temperature in a room exceeds 600°F for a specified period of time, the structural integrity of the building is compromised and the test fails. Heavy timber is a another construction type being used in buildings; it would be of use to know if and when atmosphere in a room reaches 149°F, because that is when pyrolysis of mass timber begins.

Furthermore, if the temperature in a room gets too hot and the interior finish ignites, perhaps the building loses its one-of-a-kind historical feature. In turn, the fire test would be considered failed and the stakeholder would know that the fire protection design needs to be modified to prevent that design fire scenario.

Fire spread

If a fire jumps from the storage bay where ignition occurred to another bay before the suppression systems can control it, the test might be considered a failure because the sprinkler system wasn’t robust enough to control the fire before additional property became involved. The stakeholder would know what sprinkler configuration is truly necessary, based on the proposed use of the space.

Egress

If the prescriptive requirements related to building egress, such as number of exits, distance to an exit, or hallway widths of a building cannot be met due to a retrofit or change in occupancy, then performance-based criteria might include a modeled fire in this space and a subsequent egress model to prove that the building can be fully egressed before the conditions become untenable..

These are a few examples of performance-based criteria that are tailored to the goals and objectives of the stakeholder and the expertise of the fire protection engineers.

The Society of Fire Protection Engineers provides a two-phase process of using performance-based design.

Performance-based design process

Phase 1

• Determine scope of project.
• Define the goals of the project.
• Identify the project’s objectives.
• Establish performance criteria.
• Create fire scenarios and trial designs.
• Evaluate in design brief.

Phase 2

• Determine if the design meets performance criteria
• If it does not, repeat Phase 1.
• If it does, select final design.
• Create design documents.

Building use effect on design

A building’s use and construction type are the driving factors for fire protection requirements. Every building has a related risk depending on what its purpose. In addition to several specific uses, NFPA 13 has a quantified risk based on varying occupancy and hazard classifications.

There are five occupancy types per NFPA 13:

• Light hazard.
• Ordinary hazard group 1.
• Ordinary hazard group 2.
• Extra hazard group 1.
• Extra hazard group 2.

The differences between each group are the quantified risk based on the use of the space, especially for storage, manufacturing or processing of product, as well as the quantity and volume of contents in the space, content combustibility, content heat release rate, presence of flammable or combustible liquids and intended storage heights. The use of the space is a requisite for the types of items and activities within it.

Furthermore, if the building will be used for storage, the commodity will need to be classified as class I, II, III, IV and plastics. Plastics are classified into group A, B or C. Group A is subcategorized into expanded or nonexpanded. Expanded group A plastics are “airy” plastics, such as packing peanuts or foam. Nonexpanded plastics are any other type of plastic in which the density is not reduced by air, like plastic totes for example.

Each classification has requirements in relation to what material the commodity is stored on or in, how many layers of commodity there are within the storage box, if there is extra material within the box for packing and the volume of each material in proportion to the entire package. Commodity can also be classified as exposed or nonexposed; exposed commodity is stored within packaging that absorbs water while nonexposed would be storage-wrapped in plastic so water (or any fire suppressant that would otherwise extinguish the fuel source) cannot seep in.

Whether prescriptive or performance-based, this sort of specific information is necessary to ensure appropriate protection of the hazard. Ultimately, the purpose of commodity classifications is to choose the sprinkler system best suited for the types of contents and the challenges with the method of storage. For more information on commodity classifications, read “Commodity Classifications in NFPA 13” by Brian O’Connor.

By quantifying the occupancy and commodity type, fire protection engineers can identify a potential fire scenario because they know how hot and fast specific contents burn based on historical data from general lab testing. Then, they can determine what sprinkler design components will be necessary. The design components of a sprinkler system affected by the use of the building (occupancy and commodity type) are the number of required sprinklers, sprinkler spacing, water supply requirements and potential need for a pump or a water storage tank, sprinkler density discharge, pipe sizes and system hydraulics.

Benefits & Drawbacks of Prescriptive versus Performance-based Design

A prescriptive approach and a performance-based design approach both have advantages and disadvantages. Some are listed below. Performance-based design of fire protection systems has both benefits and drawbacks. Many items here are referenced in “Performance-Based Fire Safety Design” by Morgan J. Hurley and Eric R. Rosenbaum.

Performance-based approaches are well suited for retrofit projects because fire tests could be designed to use existing pipe sizes or sprinkler types. If part of a building’s existing system is proven to be sufficient, the owner(s) can save significant spend in construction costs that would have otherwise been spent gutting and replacing an entire sprinkler system to match exactly what NFPA 13 prescriptions require. Appropriately designed performance-based systems can also provide significantly more flexibility in building use and suppression system life cycle maintenance costs for the owner.

Practical applications for performance-based design

Our world is continually evolving with new technologies and materials that currently fall outside the parameters of codes and standards in the fire protection environment. While professionals at NFPA and other regulatory agencies struggle to keep up with our evolving world, performance-based solutions function brilliantly to bridge the gap to fire safety. Additionally, user flexibility, life cycle costs, construction spend and generally improved levels of fire safety might make sense for new and future projects that are underrepresented in our current guidelines.

Examples include:

• Automatic storage retrieval systems.
• Electric vehicle charging areas.
• Car stackers.
• Lithium-ion electric bicycles sold in retail establishments.
• Green building materials not yet listed in code.
• Unique interior finishes and historical buildings.
• Unique occupancy combinations in buildings.
• Retrofitting an existing space to protect new products, processing or manufacturing models.

NFPA 13’s allowance for performance-based design can help revolutionize the industry’s knowledge of fire and protection technology. Real-world, innovative, long-term, cost-effective solutions can be developed with engineering expertise.

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