Size a total flooding system the way a design calculation is produced: design concentration from the hazard class and NFPA 2001 safety factor, agent quantity at the minimum room temperature, altitude correction, containers filled equally — and the concentration the supplied agent reaches at the maximum temperature, checked against the NOAEL. Enter the room as length × width × height, as floor area × height, or as a known volume. CO₂ follows the NFPA 12 design tables.
Size at the lowest expected room temperature, because colder vapour is denser and needs more agent. Then divide the result into containers: n = ⌈W / max fill⌉, every container filled equally. Because containers are filled up and to whole increments, the agent supplied is a little more than the agent required — and it is the supplied mass, at the highest expected temperature, that sets the peak concentration occupants could be exposed to.
| Agent | Class A (MEC × 1.2) | Class B, n-heptane (× 1.3) | Class C (Class A MEC × 1.35) | NOAEL | LOAEL |
|---|---|---|---|---|---|
| FM-200 (HFC-227ea) | 7.0% (5.8 × 1.2) listings from 6.25% | 8.7% (6.7 × 1.3) | 7.0% (5.2 × 1.35) | 9.0% | 10.5% |
| Novec 1230 (FK-5-1-12) | 4.2% (3.5 × 1.2) | 5.9% (4.5 × 1.3) | 4.7% (3.5 × 1.35) | 10.0% | >10.0% |
Class B fuels other than heptane — alcohols especially — need their own cup-burner value; use the Custom option. Where a space holds more than one hazard class, design for the highest concentration. The UL/FM listing of the hardware you install is the final authority on design concentration.
W/V = (1/S) × C/(100 − C) for HFC-227ea, sea level. Multiply by net volume to get kg. Highlighted: 7% at 20 °C.
| Temp (°C) | S (m³/kg) | 6.25% | 7% | 7.5% | 8% | 8.7% | 9% | 10% | 10.5% |
|---|---|---|---|---|---|---|---|---|---|
| 0 °C | 0.1269 | 0.5253 | 0.5931 | 0.6389 | 0.6852 | 0.7509 | 0.7794 | 0.8756 | 0.9245 |
| 10 °C | 0.1319 | 0.5054 | 0.5707 | 0.6147 | 0.6593 | 0.7224 | 0.7498 | 0.8424 | 0.8894 |
| 15 °C | 0.1344 | 0.4960 | 0.5600 | 0.6033 | 0.6470 | 0.7090 | 0.7359 | 0.8267 | 0.8729 |
| 20 °C | 0.1369 | 0.4870 | 0.5498 | 0.5923 | 0.6352 | 0.6961 | 0.7224 | 0.8116 | 0.8570 |
| 25 °C | 0.1394 | 0.4782 | 0.5399 | 0.5816 | 0.6238 | 0.6836 | 0.7095 | 0.7971 | 0.8416 |
| 30 °C | 0.1419 | 0.4698 | 0.5304 | 0.5714 | 0.6128 | 0.6715 | 0.6970 | 0.7830 | 0.8268 |
| 40 °C | 0.1469 | 0.4538 | 0.5124 | 0.5519 | 0.5919 | 0.6487 | 0.6733 | 0.7564 | 0.7986 |
| 50 °C | 0.1519 | 0.4389 | 0.4955 | 0.5338 | 0.5725 | 0.6273 | 0.6511 | 0.7315 | 0.7723 |
Lower temperature or higher concentration needs more agent. Above the 9% NOAEL, NFPA 2001 limits occupant exposure.
| Surface fires, 34% — net volume | kg/m³ | Not less than |
|---|---|---|
| Up to 3.96 m³ | 1.15 | — |
| 3.96 – 14.15 m³ | 1.07 | 4.5 kg |
| 14.15 – 45.28 m³ | 1.01 | 15.9 kg |
| 45.28 – 127.35 m³ | 0.90 | 45.4 kg |
| 127.35 – 1,415.00 m³ | 0.80 | 113.5 kg |
| Over 1,415.00 m³ | 0.74 | 1,135.0 kg |
| Deep-seated hazard | Design | kg/m³ |
|---|---|---|
| Dry electrical, spaces up to 56 m³ | 50% | 1.60 |
| Dry electrical, spaces over 56 m³ (min. 91 kg) | 50% | 1.33 |
| Record (bulk paper) storage, ducts, covered trenches | 65% | 2.00 |
| Fur storage vaults, dust collectors | 75% | 2.66 |
Small rooms get higher factors because they have more boundary — and more leakage — per cubic metre. Above 34% for surface fires, the table quantity is multiplied by the material conversion factor of NFPA 12 Figure 5.3.4 (for example about 1.67 at 50%). Openings that cannot close and ventilation that cannot shut down need additional CO₂; deep-seated hazards must reach 30% within 2 minutes and the design concentration within 7 minutes. Confirm the factors against the edition of NFPA 12 in force.
The same room protected with CO₂ for a dry electrical (deep-seated) hazard: 90 m³ is over 56 m³, so 1.33 kg/m³ × 90 = 119.7 kg (not less than 91 kg) — three 45 kg cylinders, in a space that must be normally unoccupied. To size the standby battery for the releasing panel, use the Fire Alarm Battery Calculator. For the wider design method, see the Fire Fighting System Design Calculation guide.
NFPA 2001 gives W = (V / S) × C / (100 − C), where W is the agent mass in kg, V the net protected volume in m³, C the design concentration in % and S the specific vapour volume in m³/kg at the minimum room temperature. For HFC-227ea, S = 0.1269 + 0.0005 × T, with T in °C.
At 7% design concentration and 20 °C, the flooding factor is 0.550 kg/m³. A 90 m³ room therefore needs about 49.5 kg at sea level, before the agent is divided into containers.
NFPA 2001 sets the minimum design concentration from the extinguishing concentration and a safety factor: 1.2 for Class A, 1.3 for Class B (n-heptane cup burner) and 1.35 for Class C. For HFC-227ea that gives about 7.0% for Class A and C and 8.7% for Class B. The system listing for your hardware is the final authority.
Agent is sized at the minimum expected temperature, where the vapour is densest. In a warmer room the same mass occupies more volume, so the concentration rises. For a normally occupied space that higher figure is the one compared with the NOAEL — 9.0% for HFC-227ea and 10.0% for FK-5-1-12.
Yes, at normal design concentrations. The NOAEL of HFC-227ea is 9.0% and the LOAEL is 10.5%. Between the two, NFPA 2001 limits exposure time and requires that occupants can leave promptly; above the LOAEL it is not permitted in normally occupied spaces.
NFPA 12 uses flooding factors that depend on the room volume, because small rooms leak proportionally more. For surface fires at 34%, a 90 m³ room uses 0.90 kg/m³ — 81 kg — compared with about 68 kg from the theoretical equation. Deep-seated hazards use higher factors, such as 1.33 kg/m³ for dry electrical rooms over 56 m³. CO2 at these concentrations is lethal, so it is only used in normally unoccupied spaces.
Air is less dense at altitude, so less agent is needed to reach the same volume concentration. NFPA 2001 gives an atmospheric correction factor — 0.96 at 300 m and 0.93 at 610 m, for example. Using the factor for the table altitude at or below the site, rather than interpolating, is the conservative choice.
Yes. Choose "Area × Height" and enter the floor area from the drawing with the room height; the net volume is area × height minus any solid objects. If you already know the protected volume, choose "Volume" and enter it directly.
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