Egress Speed for NFPA 2001 Egress Time Study?

4/9/2025

NFPA 2001, Standard on Clean Agent Fire Extinguishing Systems now require an egress time study to show that the design limits exposure to halocarbon agents is no longer than 5 minutes, like FK-5-1-12 (NOVEC 1230), HFC-227ea (FM 200).

This comes from 2018 Edition Section 1.5.14, 2020 Edition Section 4.3.4, and 2022 Edition Section 4.3.4.

Exposure time for inert gas agents will depend on the oxygen levels within the space or room. Concentration below 43 percent shall be permitted where exposure is no longer than 5 minutes. Concentration between 43 and 52 percent shall be permitted where exposure is no longer than 3 minutes.

The annex of NFPA 2001 tells us to review the NFPA Handbook and the SFPE Handbook for more information.

Is anyone doing these calculations, and if so, what exit flow, movement speed, and reaction time would you consider appropriate for spaces using these systems?

Thanks in advance.

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6 Comments

Jesse

4/9/2025 09:18:38 am

I have to preface my response with these comments are mine, and I'm not speaking for the NFPA 2001 technical committee, etc etc etc.

The annex references SFPE Handbook 5th edition. The ASET time is how much time is available to make a safe egress and we balance that with the RSET, which is the required time element to make a safe egress. For reasons that are probably obvious, the ASET neds to be less than the RSET.

While the SFPE Handbook gives a few iodeas of how we can find the ASET, in my humble opinion an actual egress study works fine and is allowed by the standard. This would be normal occupant load for the space, and simply timing how long it takes the occupants to move to a safe area.

Its not unlike how the FAA measures how long it takes to evacuate an airplane.And we expect occupants to leave their belongings (if any) and just get out.

One advantage is that the people working in this area are highly likely to be intimately familiar with the layout and the means of egress.

If the ASET Value is less than the RSET Value, all is well. If the ASET is equal to or higher than the RSET, we need to improve routes of egress.

Hope this helps

Joe

4/9/2025 10:52:09 am

Several factors must be reviewed to complete the time egress study this including the
following items:
Agent type and design concentration
Occupant load
Exit Routes
Exit Availability
Exit Width
Travel Distance
Evacuation Time Factors
Reaction Time
Movement Time
Exit Flow

Evacuation time = Rection time + Movement time + Exit time

reaction time for occupants to perceive the alarm and begin
evacuation is typically assumed to be around 30 to 60 seconds under normal conditions may be higher.

Movement time = {travel distance to exit ÷ travelspeed} × (number of occupants) When reviewing travel speed, what about people that are in a wheel chair or other factor

Exit time = number of exits ÷ (flow rate × width of exit)

Chris Nelson

4/11/2025 08:30:45 am

This is backwards. RSET should be less than ASET.

The required time should less than available time. If the required time is more than the available time, people are dead.

Chad

4/9/2025 11:32:46 am

Are there rooms that are large enough where RSET would ever be greater than 3 or 5 minutes where there is an agent system? I am looking for an example so I can wrap my brain around why you would need to perform the calc?

Given that the space will always have A/V notification devices so reaction time would never be more than 10 seconds or so?

I guess I could see a performance based design that might need that but prescriptive?

4/9/2025 01:20:46 pm

Data center and other spaces like them can take that long.

Please look as SFPE handbook and NFPA handbook, they tell us to use a reaction time at minimum 30-69 second under normal conditions.

The travel speed for can be around 3 feet per second on flat ground and even lower if there are mobility occupants. ( wheelchair, walkers and other issues)

I would be afraid to use a number that is faster then the handbooks talks about.

Ricardo Gonzales Jr

4/9/2025 03:13:54 pm

When looking at the concentrations, be sure not to confuse the agent concentration with O2 concentration. O2 is maxed out at 20.6% at sea level and holds fairly well as elevation increases. It's agent concentration that changes as air pressure is lessened. i.e. at sea level the O2 pressure is 14.7psi, but at 6,000 feet the pressure drops to 11.8psi. O2 is still 20.6% makeup but of only 11.8 psi. Takes less agent to get the same % of concentration in the room. When atmosphere pressure gets below a certain point, our bodies no longer can absorb O2 out of the air. It's the agent exposure that is of concern.

Egress Speed for NFPA 2001 Egress Time Study?

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