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NFPA 12 · SFPE Handbook Ch. 45

CO₂ Total-Flooding Calculator — Surface (Pool) Fires

Compute the final design quantity (mFD) of carbon dioxide for a surface-fire total-flooding system. Implements the full six-step procedure: protected volume, minimum extinguishing concentration, design concentration, base flooding factor, material conversion factor, leakage through uncloseable openings, mechanical ventilation, and temperature-extreme adjustments.

Internal calculations in SI; both unit sets give the same physical answer.

Step 1 Enclosure & protected volume

Net protected volume VP = gross enclosure volume minus the volume of fixed solid, impermeable objects (pillars, machinery, etc.).

m³
m³

Step 2 Minimum extinguishing concentration (MEC)

Per NFPA 12 Table 5.3.2 (excerpted as Table 45.14). Pick a material to autofill MEC and the table design concentration, or supply MEC directly, or derive it from a residual-oxygen value via Eq. 45.10.

Table 45.14 / NFPA 12. MEC and DC are theoretical values; many liquids round DC up to the 34 vol.% minimum.
vol.%
Autofilled from material; switch to “Manual MEC” to override.

Step 3 Design concentration (DC)

DC = MEC × (1 + safety factor), with a minimum of 34 vol.%. NFPA 12 default safety factor is 20 %.

%
vol.%
NFPA 12 default = 34 vol.%.
vol.%
e.g. set to Table 45.14 DC value if you want to use the tabulated value.

Step 4 Base design quantity (mBD)

mBD = VP × FF, where FF is the volume-banded flooding factor from Table 45.15. Cannot be less than the minimum quantity for the band.

FF is auto-selected from VP. Bands and minimums are calibrated at 34 vol.%; if DC > 34 vol.%, Step 5a applies the material conversion factor.

Step 5a Material conversion factor (MCF)

For DC > 34 vol.%, scale mBD by MCF (Eq. 45.12): MCF = 2.41 · ln(100 / (100 − DC))

Auto-applied based on Step 3. MCF = 1.00 when DC ≤ 34 vol.%.

Step 5b Leakage through uncloseable openings (mlo)

CO₂ lost in the first minute through openings that cannot be closed before discharge. Set area to zero if none.

m²
m
min
Surface fires: 1 min (design concentration must be reached within 1 min).

Step 5c Mechanical ventilation (mlv)

CO₂ lost to forced ventilation that cannot be shut down before discharge: mlv = QV · t · FF (Eq. 45.16).

m³/s
s
Surface fires: 60 s.

Step 5d Temperature extremes (mT)

Adjust for ambient temperatures outside −18 to 93 °C (0 to 200 °F). Leave at “normal” values if not applicable.

°C
No adjustment if TH ≤ 93 °C (200 °F).
°C
No adjustment if TL ≥ −18 °C (0 °F).

Step 6 Final design quantity

mFD = mcf + mlo + mlv + mT   (Eq. 45.22)

VP
—m³
 
MEC → DC
— → —vol.%
 
Flooding factor (FF)
—kg/m³
 
Material conversion factor
—
 
Step Quantity Value (kg) Equivalent (lb) Notes
4 mBD — base design quantity — —
5a mcf — after material conversion factor — —
5b mlo — leakage through openings — —
5c mlv — ventilation losses — —
5d mT — temperature-extreme adjustment — —
6 mFD — final design quantity — —
Final design quantity (mFD)
—kg
—
Minimum discharge rate (surface fire)
—kg/min
DC reached within 1 min of discharge start
CO₂ storage volume (ref.)
—m³
Vapor at 30 °C, expansion 0.56 m³/kg
Concentration check (Eq. 45.9)
—vol.%
Theoretical C from mcf alone (free-efflux)

Method & equations

This calculator implements the surface-fire design procedure for total-flooding CO2 systems as presented in SFPE Handbook, Ch. 45 “Carbon Dioxide Systems” (Harrington & Senecal), which references NFPA 12. The six steps are:

Step 1 — Protected volume

VP is the gross enclosure volume less the volume of fixed solid, impermeable objects (e.g. pillars, large equipment). All interconnected spaces where CO2 can freely flow are included.

Step 2 — Minimum extinguishing concentration (MEC)

The theoretical MEC may be looked up from Table 45.14 or, if the maximum residual oxygen O2 is known, calculated from:

%CO₂ = ((21 − O₂) / 21) × 100    (Eq. 45.10)
MaterialMEC (vol.%)DC (vol.%)
Acetone2734
Acetylene5566
Carbon disulfide6072
Ethyl alcohol3643
Hexane2935
Methyl alcohol3340
Propane3036

Step 3 — Design concentration (DC)

DC = max(MEC × (1 + SF), 34 vol.%)

NFPA 12 requires a safety factor of at least 20 % on MEC, with a floor of 34 vol.%. You may instead enter the DC value listed in Table 45.14 directly via the override.

Step 4 — Base design quantity

mBD = max(VP × FF, mmin)    (Eq. 45.11)

Flooding factors are calibrated at 34 vol.% with a CO2 expansion factor of 0.56 m³/kg (9 ft³/lb) at 30 °C (86 °F). They include an inherent normal-leakage safety factor for VP ≤ 1415 m³ (50,000 ft³). Table 45.15:

VP band (m³)FF (kg/m³)Min mBD (kg)VP band (ft³)FF (lb/ft³)Min mBD (lb)
≤ 3.961.15—≤ 1400.072—
3.97 – 14.151.074.5141 – 5000.06710
14.16 – 45.281.0115.1501 – 16000.06335
45.29 – 127.350.9045.41601 – 45000.056100
127.36 – 14150.80113.54501 – 50,0000.050250
> 14150.741135> 50,0000.0462500

Step 5a — Material conversion factor

MCF = 2.41 · ln(100 / (100 − DC))    (Eq. 45.12)
mcf = mBD × MCF    (Eq. 45.13)

Applies only when DC > 34 vol.%; otherwise MCF = 1.0 and mcf = mBD.

Step 5b — Leakage through uncloseable openings

mlo = 116 · A · √(ρ1 · (ρ1 − ρA) · h) · t    (Eq. 45.14, SI — kg, m², m, min)
mlo = 0.6 · C · ρCO₂ · A · √(2g(ρ1 − ρA)h / ρ1) · t    (Eq. 45.15, US — lb, ft², ft, min)

At 1 atm and 21 °C (70 °F): ρCO₂ = 1.825 kg/m³ (0.114 lb/ft³); ρA = 1.202 kg/m³ (0.0751 lb/ft³); ρ1 = 0.00622·C + 1.202 kg/m³ (0.000388·C + 0.0750 lb/ft³). If the opening is on a wall without a comparable opening near the ceiling, half of A is used (half of the opening allows CO2/air efflux while the other half admits outside makeup air).

Step 5c — Mechanical ventilation

mlv = QV · t · FF    (Eq. 45.16)

QV is the volumetric flow of fresh air introduced by mechanical ventilation that cannot be shut down. For surface fires, t = 60 s.

Step 5d — Temperature extremes

For high temperatures (TH > 93 °C / 200 °F), add 0.36 % per °C (1 % per 5 °F). For low temperatures (TL < −18 °C / 0 °F), add 1.8 % per °C (1 % per °F).

τH = 0.0036 · (TH − 93 °C)    (Eq. 45.17)
τL = 0.018 · (−18 °C − TL)    (Eq. 45.18)
mT = τ · (mcf + mlo + mlv)    (Eq. 45.21)

τ = max(τH, τL, 0). If both extremes are present, use whichever gives the larger factor.

Step 6 — Final design quantity

mFD = mcf + mlo + mlv + mT    (Eq. 45.22)

The minimum discharge rate for surface fires must be sufficient to reach DC within one minute of the start of discharge: rate ≥ mFD / 1 min.

Concentration check (informational)

m = (VP / s) · ln(100 / (100 − C))    (Eq. 45.9, free-efflux)

With s = 0.56 m³/kg (CO2 vapor at 30 °C), inverting Eq. 45.9 with m = mcf gives the theoretical concentration achieved by the base-plus-MCF charge alone (excluding losses).

Scope & limitations

Source & credit

The design procedure, equations, and tables (45.14 / 45.15) implemented here are taken from:

Harrington, J. and Senecal, J.A., “Carbon Dioxide Systems,” Chapter 45 in the SFPE Handbook of Fire Protection Engineering, Society of Fire Protection Engineers. Equation and table numbering (Eqs. 45.9–45.22, Tables 45.14–45.16) corresponds to that chapter, which is in turn based on NFPA 12 Standard on Carbon Dioxide Extinguishing Systems.

All credit for the underlying engineering methodology belongs to the original authors and to the NFPA 12 Technical Committee. This tool is an independent implementation of their published procedure.

Engineering aid only. This tool implements the published surface-fire CO2 design procedure per NFPA 12 / SFPE Handbook Ch. 45. It is not a substitute for independent review by a qualified fire protection engineer. The user is responsible for verifying the applicability of the standard, validating inputs and assumptions (enclosure tightness, residual oxygen targets, ventilation interlocks, etc.), and the final system design. CO2 total-flooding systems present a life-safety hazard to occupants; egress, lockout, pre-discharge alarms, and personnel safety provisions are outside the scope of this tool.