All three are clean agents covered by NFPA 2001-2025, but they work differently. HFC-227ea and FK-5-1-12 are halocarbons that extinguish at a low volume percentage; IG-541 is an inert gas blend (N₂ 52 %, Ar 40 %, CO₂ 8 %; Table 1.1.1) that extinguishes by diluting oxygen. Every number below comes from a clause or table of the standard; Annex A values are informative and a design uses the listed value of the system.
Short answer: the informative Class A design concentration is 6.7 % for HFC-227ea, 4.5 % for FK-5-1-12 and 34.2 % for IG-541. At 21 °C (70 °F) that means 0.523 kg, 0.653 kg and 0.419 m³ (0.591 kg) of agent per m³. Halocarbons discharge in 10 seconds, IG-541 in 120 seconds for Class A and C. The GWP is 3350 for HFC-227ea, <1 for FK-5-1-12 and 0 for IG-541 (Table A.4.6).
Side by side: NFPA 2001-2025 values
| Criterion | HFC-227ea (FM-200) | FK-5-1-12 (Novec 1230) | IG-541 (Inergen) |
|---|---|---|---|
| Agent type (Table 1.1.1) | Halocarbon | Halocarbon | Inert gas: N₂ 52 %, Ar 40 %, CO₂ 8 % |
| Storage form | Liquefied compressed gas at 21 °C (A.5.1.4.1) | Liquefied compressed gas at 21 °C (A.5.1.4.1) | Single-phase gas in storage and discharge (A.5.1.4.6(2)) |
| Class A MEC (Table A.7.2.2.3(b)) | 5.2 % | 3.3 % | 28.5 % |
| Class A minimum design | 6.7 % | 4.5 % | 34.2 % |
| Class C minimum design | 7.0 % | 4.5 % | 38.5 % |
| n-heptane extinguishing (Table A.7.2.2.2.1) | 6.62 % | 4.5 % | 34.4 % |
| NOAEL / LOAEL (Table 4.3.2.4(a)) | 9.0 % / 10.5 % | 10.0 % / >10.0 % | Not applicable; oxygen bands (4.3.3.5) |
| Maximum discharge time (7.5.1) | 10 s | 10 s | 60 s Class B · 120 s Class A and C |
| GWP (IPCC 2013) / ODP (Table A.4.6) | 3350 / 0 | <1 / 0 | 0 / 0 |
| Recovery (A.5.1.4.2) | Recycling return label recommended | Recycling return label recommended | Need not be collected or recycled |
The design concentration rule is the same for all three: for Class A, the listed MEC × 1.2 (automatic actuation) or × 1.3 (manual-only actuation), and not less than the n-heptane value (7.2.2.1.2); for Class B, the fuel value × 1.3 (7.2.2.2.3); for Class C, Class A MEC × 1.35 (7.2.2.4.1).
Quantity per m³ at 21 °C
Halocarbon quantity follows Equation 7.3.1 and inert gas quantity Equation 7.3.2. The specific volume s comes from the s = k1 + k2·t expression printed under the Annex A flooding tables (Tables A.7.3.1(j), A.7.3.1(b), A.7.3.2(f)).
| Agent and concentration | s (21 °C) | Quantity per m³ | 100 m³ room |
|---|---|---|---|
| HFC-227ea, Class A 6.7 % | 0.1374 m³/kg | 0.523 kg/m³ | 52.3 kg |
| HFC-227ea, Class C 7.0 % | 0.1374 m³/kg | 0.548 kg/m³ | 54.8 kg |
| FK-5-1-12, Class A and C 4.5 % | 0.0722 m³/kg | 0.653 kg/m³ | 65.3 kg |
| IG-541, Class A 34.2 % | 0.7082 m³/kg | 0.419 m³/m³ (0.591 kg/m³) | 41.9 m³ (59.1 kg) |
| IG-541, Class C 38.5 % | 0.7082 m³/kg | 0.486 m³/m³ (0.687 kg/m³) | 48.6 m³ (68.7 kg) |
By mass the three agents look close; the difference is the storage form. Halocarbons are stored as a liquid (A.5.1.4.1). IG-541 carries gas that would occupy 41.9 m³ at 21 °C and 1.013 bar as a single-phase compressed gas (A.5.1.4.6(2)). Cylinder count and fill pressure are not in the standard; they come from the system's listed manual.
Effect of temperature
Quantity is calculated with the specific volume at the minimum anticipated temperature (7.3.1, 7.3.2), and the concentration the same quantity produces at the maximum temperature is also calculated and recorded (7.3.1.1, 7.3.2.3, 7.3.1.2). A cold room needs more agent; a hot room raises the concentration:
| Agent (Class A) | Per m³ at 0 °C | Increase over 21 °C | C at 40 °C if sized for 0 °C | Limit |
|---|---|---|---|---|
| HFC-227ea 6.7 % | 0.566 kg/m³ | +8.3 % | 7.67 % | NOAEL 9.0 % |
| FK-5-1-12 4.5 % | 0.710 kg/m³ | +8.7 % | 5.20 % | NOAEL 10.0 % |
| IG-541 34.2 % | 0.451 m³/m³ | +7.6 % | 38.08 % | 43 % band (4.3.3.5(1)) |
For Class C, IG-541 at 38.5 % sized for 0 °C reaches 42.7 % at 40 °C, very close to the 43 % limit. In a room with a wide temperature range the maximum temperature check must not be skipped.
Personnel safety
Halocarbons: normally occupied spaces may be designed up to the NOAEL (4.3.2.4(1)). For HFC-227ea, going above the NOAEL is possible only where PBPK Table 4.3.2.4(c) allows 5 minutes: 5 min up to 10.5 %, 1.13 min at 11.0 %, 0.49 min at 12.0 %; concentrations with less than 5 minutes allowable exposure are not permitted in normally occupied spaces (4.3.2.4(2), (3)). This edition has no PBPK table for FK-5-1-12; its LOAEL is listed only as “>10.0 %”. In every case exposure is limited to 5 minutes (4.3.2.1) with a pre-discharge alarm and time delay (4.3.2.3).
IG-541: the limit is oxygen depletion (4.3.3.5). Below 43 % (sea-level equivalent O₂ 12 %) is permitted with exposure limited to 5 minutes; 43–52 % with 3 minutes; 52–62 % only in normally unoccupied spaces with exposure under 30 seconds; above 62 % only where personnel are not exposed. Inert gas design also considers the Table 7.3.3.3 altitude factors (4.3.3.2).
Discharge and hold time
HFC-227ea and FK-5-1-12 must discharge within 10 seconds (7.5.1.1). IG-541 must discharge within 60 seconds for Class B fuel hazards and 120 seconds for Class A surface-fire and Class C hazards (7.5.1.2). Discharge time is the time to discharge 95 % of the agent mass needed for the minimum design concentration based on a 20 % safety factor (3.3.13). The hold requirement is the same for all three: at least 85 % of the minimum design concentration at the highest height of protected content for 10 minutes or long enough for trained personnel to respond (7.4.1).
Looking for an FM-200 alternative: what the standard compares
- Concentration and exposure: the gap between the FK-5-1-12 Class A design (4.5 %) and its NOAEL (10.0 %) is larger than for HFC-227ea (6.7 % and 9.0 %). For IG-541 the comparison is not against a NOAEL but against the 4.3.3.5 oxygen bands.
- Environmental values: Table A.4.6 lists a GWP of 3350 for HFC-227ea, <1 for FK-5-1-12 and 0 for IG-541; all three have an ODP of 0. A.4.6 recommends avoiding unnecessary emission of agents with non-zero ODP or GWP and not performing unnecessary discharge tests.
- Raised floors: where only the underfloor space is protected, an inert gas shall be used (7.1.6.1).
- Altitude: where pressure differs from sea level by more than 11 %, the quantity is corrected with Table 7.3.3.3; the factor at 5,000 ft (1.52 km) is 0.82 (7.3.3.3).
Changing agent changes the whole system: listed concentration, nozzles, pipe flow calculation (Section 6.2) and discharge time are set again from the listing of the new system.
Frequently Asked Questions
Can IG-541 be used as an FM-200 (HFC-227ea) alternative?
NFPA 2001-2025 accepts both agents in occupied spaces within their limits; the choice follows from design concentration, exposure limits, discharge time and storage form. The informative Class A design concentration is 6.7 % for HFC-227ea and 34.2 % for IG-541 (Table A.7.2.2.3(b)). The actual value comes from the system listing.
How much agent is needed per m³ at 21 °C?
With the Annex A Class A design values and the NFPA 2001 equations: HFC-227ea 0.523 kg/m³ (7.3.1), FK-5-1-12 0.653 kg/m³ (7.3.1), IG-541 0.419 m³/m³, i.e. 0.591 kg/m³ (7.3.2). The values depend on the specific volume taken at the minimum design temperature.
Which agent has the larger personnel safety margin?
For halocarbons the design concentration is compared with the NOAEL (Table 4.3.2.4(a)): HFC-227ea 6.7 % against a NOAEL of 9.0 %; FK-5-1-12 4.5 % against a NOAEL of 10.0 %. For IG-541 the limit is oxygen: below 43 % is permitted with exposure limited to 5 minutes (4.3.3.5(1)); 34.2 % is inside that band.
Why are the discharge times different?
NFPA 2001 limits halocarbon discharge to 10 s (7.5.1.1). For inert gases the limit is 60 s for Class B fuels and 120 s for Class A surface-fire and Class C hazards (7.5.1.2).
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Download MEP Calc on the App StoreNFPA 2001 Standard on Clean Agent Fire Extinguishing Systems, 2025 edition: Table 1.1.1; 3.3.13; 4.3.2–4.3.3.5 and Tables 4.3.2.4(a), (c); 7.1.6.1; 7.2.2; 7.3.1–7.3.3.3 and Table 7.3.3.3; 7.4.1; 7.5.1; Annex A: A.4.6 and Table A.4.6, A.5.1.4.1, A.5.1.4.2, A.5.1.4.6(2), Tables A.7.2.2.2.1, A.7.2.2.3(b), A.7.3.1(b), A.7.3.1(j), A.7.3.2(f). Annex A values are informative; a design uses the values from the system listing.