Your questions answered: Fire and life safety suppression systems

Unanswered questions from the July 21 fire suppression webcast are answered here

By Joshua D. Greene August 19, 2022
Courtesy: Consulting-Specifying Engineer

Fire suppression design is one of the most important aspects of fire and life safety engineering. Every project has unique requirements, and engineers should understand planning and implementing fire protection systems for a wide range of building types and hazard levels.

Fire suppression frequently includes a sprinkler system to extinguish or contain a fire. Suppression systems include water-based, wet, dry, pre-action systems, clean agent, foam, mist and a host of specialty systems. These systems are considered active fire suppression.

In this Q&A, questions from the July 21 “Suppression systems” webcast are answered. Learn more from Joshua D. Greene, PE, Simpson Gumpertz & Heger, Waltham, Massachusetts.

Carbon dioxide systems are regulated separately in NFPA 12: Standard on Carbon Dioxide Extinguishing Systems to include additional requirements for alerting occupants of an impending discharge. Courtesy: Consulting-Specifying Engineer

Fire suppression insights

  • This Q&A helps the engineer assess the various active fire suppression systems available, and which ones are appropriate to specify in the design.
  • The discussion touches on specialty fire suppression systems and their uses, and provides details beyond the live webcast.

In your case study for room 2 with the clean agent system, does rack height enter into the design like the room 1 wet sprinkler system?

No. Clean agent systems must meet an effective concentration of the agent. Most systems are designed as total flooding, meaning the concentration is maintained throughout the enclosed room being protected. In a total flooding design, the concentration calculation is based on the volume of the room. The only impact the racking has is the volume of it and its contents within a room. When designing for concentration, the volume used is the total room volume minus the volume of fixed items that are impervious to the clean agent gas.

What is the difference between clean agent and carbon dioxide system?

The primary difference isn’t in the agent composition, but rather the impact of carbon dioxide suppression systems in comparison to clean agent suppression systems. Clean agent systems, which include inert gases composed primarily of argon, helium, neon or nitrogen, are designed at concentrations that lower the oxygen level below that needed for combustion, but still above that needed for humans to breathe. Carbon dioxide systems, however, are designed at concentrations that lower the oxygen level below what is needed for humans.

As a result, carbon dioxide systems are regulated separately in NFPA 12: Standard on Carbon Dioxide Extinguishing Systems to include additional requirements for alerting occupants of an impending discharge. The concentrations of carbon dioxide are also significantly higher than clean agents, so lumping CO2 into the clean agent standard would require an entire section dedicated to its design characteristics.

What is the biggest challenge the designer encounters when preparing drawings? For hydraulically calculated sprinkler systems, what level of confidence do designers have in a single flow test report and how do they address any concerns?

For new buildings, in my opinion the biggest challenge is keeping up with the evolution of the building design. Depending on the design team, a building can reach a design level commensurate with preliminary design of a sprinkler system anywhere from the end of schematic design (SD) all the way to 50% construction documents (CD). For those buildings that don’t take final form until the CD phase, preparing design drawings during SD and design development (DD) can be frustrating. In many cases, specific hazards for which the sprinkler design must account are not known until the CD phase and they can significantly alter a design.

With respect to the question regarding the confidence in a flow report, the answer depends on when and where the flow was taken. Many larger municipalities can now give you good water supply information for a hydrant location without an actual flow test. Projects in smaller municipalities and rural areas will still rely on actual hydrant flow tests in the field. The designer needs to rely on the test results for the design, but good practice is to require the sprinkler contractor to perform a new flow test (or get new flow data) within six months of their design to confirm the original flow data is still appropriate.

What system design for main electrical rooms and simple information technology rooms?

The fire protection or suppression system used in main electrical rooms and simple IT rooms is going to be dependent on the risk tolerance of the owner/end user. Despite a historic aversion to water-based fire protection systems in these rooms, wet sprinkler system protection is the most common method applied. If the IT room contains equipment that serves critical systems (e.g., data systems for patient health information in a hospital), it may be prudent to use a pre-action system to minimize the chance for inadvertent discharge withing the room. Some users request gaseous clean agent as the primary system, with pre-action as the backup system if the equipment or data being processed is essential.

It is important to remember that many buildings are required by the building code to be sprinkler-protected throughout. This includes data and electrical rooms. If an end user or owner requests protection only with a clean agent system, this does not meet the sprinkler code requirement unless the jurisdiction specifically approves its use without a backup sprinkler system. Also, despite the fact that electrical rooms and IT rooms can be protected by sprinklers, damage from inadvertent water leaks or discharge is a valid concern; good design practice it to limit the sprinkler piping in these rooms to only that needed to supply the sprinkler protection. Good designers don’t run sprinkler mains or other sprinkler piping through these rooms.

How to deal with a renovation job that doesn’t give much information on the existing system: Are there any reasonable assumptions that can be made, or is a site visit required to be able to integrate the new system?

You will need to apply engineering judgment in these instances, though I will say that we typically choose to do an on-site evaluation of an existing fire protection system that is being modified as part of a renovation. Relying on the accuracy of previous design or as-built drawings can be problematic, especially when the system is older and may have been modified for other renovations in the past. Simple tenant fit-outs for new buildings that were originally designed as a core and shell may not require an on-site inspection, but even those projects introduce some uncertainty and require design assumptions that the available data is accurate.

Is it possible to implement the water mist system in areas of electrical generation, such as transformer areas?

Yes, water mist fire protection is appropriate and often used for protection of power generation equipment such as transformers and turbines.

Which extinguishing agent can support the case of wet chemical systems?

Wet chemical agents for suppression of kitchen fires should be tested and listed to ANSI/UL 300, Fire Testing of Fire Extinguishing Systems for Protection of Commercial Cooking Equipment.

Who is responsible for maintaining the standpipes in a high-rise building? Owner? Fire protection designer? Installer? Is there regular maintenance that needs to be done? If so, who should do it?

Owners are responsible for maintenance of fire protection systems withing their building, including standpipe systems. Most Fire Codes will reference NFPA 25: Standard for the Inspection, Testing and Maintenance of Water-Based Fire Protection Systems , for maintaining water-based systems. Standpipes and hose systems have their own chapter within this standard. Be sure to apply the correct edition of NFPA 25; the fire code will reference the specific edition that s applicable for the jurisdiction.

Why are you recommending backup systems? Is this based on client requirements?

Backup, or secondary, systems such as pre-action are often used to meet a building code requirement that a building be sprinkler-protected throughout. This includes rooms where, because of the presence of critical equipment or owner/end user requests, water-based systems are not preferable as the primary means of fire protection/suppression. If an end user or owner requests protection only with a clean agent system, this does not meet the building code requirement for sprinkler protection throughout the building; the inclusion of a secondary pre-action system in the room achieves that code requirement.

It is also good practice to provide a secondary water-based system in many areas where clean-agent systems are used as the primary suppression method. Remember, clean agent systems are single application; once the system discharges, there is no continuous or backup supply if the fire isn’t extinguished. Providing a pre-action system maintains protection for the room in cases where clean-agent discharge didn’t extinguish the fire.

In limited cases, the jurisdiction may allow protection of a room with only clean agent, but also then require that the enclosure have a fire resistance rating. The enclosure rating is assumed to provide passive protection so that a fire doesn’t spread beyond the enclosure until the fire department arrives to manually suppress the fire.

How far can the clean agent tanks be from the area of protection?

It depends on the agent being used. Each agent has different flow characteristics; manufacturers should be included in the design process to assist with flow calculations and location of agent storage cylinders.

What kind of piping do you spec for a pre-action system?

This is likely a designer preference. Some designers use galvanized steel for pre-action systems. Others use normal black steel piping. If there are concerns regarding corrosion, which tends to occur more often in systems that don’t normally have water-filled pipe, galvanized or black steel with larger pipe thickness (i.e., Schedule 40 instead of Schedule 10) is often recommended.


Author Bio: Joshua D. Greene is Associate Principal at Simpson Gumpertz & Heger, Waltham, Massachusetts. He is a member of the Consulting-Specifying Engineer editorial advisory board.