Teknik·10 min read
FM200 Clean Agent Suppression: Volume Calculation, NOAEL/LOAEL and Design Engineering
The engineering details that make an FM200 system work on site, not just on paper: which volume can be deducted from the agent calculation, suspended-ceiling and raised-floor voids, the difference between a contact-output pressure gauge and a pressure switch, when ventilation and dampers must close, and the NOAEL/LOAEL safety thresholds.
A-Pro Mühendislik
FM200 (chemically HFC-227ea) has been used for decades as a clean-agent suppressant in electrical and electronic spaces where water would cause damage. Its main advantage is compact storage: it delivers high suppression capacity in a small number of cylinders, which is why it remains a preferred choice on projects with limited cylinder-room space. We covered which agent to choose in which situation, and a full agent-family comparison, in Gas Suppression: Design and Agent Selection. This article drills into a single agent — FM200 — from an engineering standpoint, in the order a design actually follows: first we determine the space’s hazard class to find the design concentration, check it against the NOAEL/LOAEL safety thresholds, then calculate the agent quantity and net volume (what may be deducted), solve the suspended-ceiling/raised-floor voids, and finally cover the system devices and the ventilation/damper automation.
Suppression mechanism and discharge time
FM200 extinguishes primarily by absorbing heat — it draws away the heat the flame needs to sustain itself and partially interrupts the combustion chain reaction. It is stored liquefied and super-pressurised with nitrogen (typically 25 / 42 / 50 bar), and on release rapidly vaporises to fill the space homogeneously.
A critical design rule is that discharge must complete in 10 seconds or less. There are two reasons: (1) to reach design concentration quickly and suppress the fire early, and (2) because FM200 releases some hydrogen fluoride (HF)-type decomposition products at high temperature, shortening the agent’s exposure to flame minimises their formation. Fast discharge is therefore mandatory for both suppression performance and safety.
Hazard classes and design concentration
The starting point of any FM200 design is to determine the fire hazard class of the space, because the design concentration (C) used in the volume calculation depends on it. In Turkey gas-suppression design is based on ISO 14520 (TS ISO 14520). ISO 14520 defines the design concentration by applying a safety factor (×1.3) to the measured extinguishing concentration, and uses three hazard classes. Key difference: NFPA 2001’s “Class C” (energised electrical) is not a separate class in ISO 14520 — it is handled within ISO’s Class A – High hazard. Values for FM200 (HFC-227ea) per ISO 14520-9 (Table 4):
| Class | Concentration basis (ISO 14520) | FM200 design concentration |
|---|---|---|
| Class A — Surface | Highest of wood-crib / PMMA / PP / ABS extinguishing values × 1.3 | 7.9% |
| Class A — High hazard | Greater of Surface Class A or 95% of the Class B design | 8.5% |
| Class B — Flammable liquid | Heptane (cup-burner) extinguishing value × 1.3 | 9.0% |
- Class A – Surface (surface fire): surface burning of solid combustibles (paper, wood, plastic, textiles, cable insulation) — the primary application of clean agents. For FM200 the highest extinguishing value (PMMA/PP/ABS 6.1%) × 1.3 = 7.93% → 7.9%.
- Class A – High hazard: spaces with a dense fuel load (cable bundles, filled cable trays) or where equipment stays energised during extinguishment. ISO 14520-9 defines this concentration as the greater of Surface Class A (7.9%) or 95% of the Class B design (0.95 × 9.0% = 8.55%) → 8.5%. NFPA 2001’s separate “Class C” (energised electrical) maps into this class in content.
- Class B – Flammable liquid: flammable/combustible liquid fires; requires the highest concentration; heptane cup-burner value (6.9%) × 1.3 → 9.0% for FM200.
Which class a space falls into — the definitions of the three classes, the four high-hazard conditions of ISO 14520-1 clause 7.5.1.3 (cable bundle >100 mm · tray fill >20% · tray stacks <250 mm apart · energised >5 kW) and the “which space, which class” table — is agent-independent; for the detail, see the hazard-class determination section of our Gas Suppression: Design and Agent Selection article. In brief: energised data center/server/telecom rooms meet condition 4 (energised + >5 kW) by default and are therefore treated in practice as Class A – High hazard (8.5%); the Surface (7.9%) value is for de-energised, low-cable-load spaces (archive, small electrical room). In unoccupied, flammable-liquid-dominated spaces (generators, turbines), CO₂ is often considered instead of FM200.
NOAEL and LOAEL: human-safety thresholds
Once the hazard class has set the required design concentration, the second question is: is that concentration safe for people? In occupied spaces (server rooms, control rooms, electrical panel rooms), two thresholds decide this:
- NOAEL (No Observed Adverse Effect Level): the highest concentration producing no observable adverse physiological effect in humans. For FM200 it is 9%.
- LOAEL (Lowest Observed Adverse Effect Level): the lowest concentration at which an adverse effect begins to appear. For FM200 it is 10.5%.
The rule: the design concentration required for suppression must stay below the human-safety threshold (NOAEL). This is what gives the previous section’s numbers their meaning: Class A – Surface 7.9% leaves a safe margin to NOAEL (9%). Class A – High hazard 8.5% approaches NOAEL (9%); the margin is only ≈0.5 points. Since data centers and server rooms are usually Class A – High hazard (8.5%), the margin is tight in these occupiable spaces; the egress and pre-discharge delay time therefore become critical. Class B 9.0% is effectively at the NOAEL level (9%); Class B spaces are therefore usually unoccupied technical rooms, with egress/delay-time limits applied rigorously. At A-Pro we always keep the design concentration on the safe side in occupied spaces.
Agent quantity and volume calculation
The required FM200 mass is calculated with the ISO 14520 / NFPA 2001 formula:
W = (V / s) × (C / (100 − C))
- W = required agent mass (kg)
- V = protected net free volume (m³)
- C = design concentration (%)
- s = agent specific volume (m³/kg), temperature-dependent: for FM200, per ISO 14520-9, s = 0.1269 + 0.000513 × T (T = space temperature °C)
Example: a server room with 100 m² floor area and 3 m height (V = 300 m³), T = 20 °C. Since the equipment stays energised throughout extinguishment, the space is Class A – High hazard, C = 8.5%:
s = 0.1269 + 0.000513 × 20 ≈ 0.1372 m³/kg
W = (300 / 0.1372) × (8.5 / 91.5) ≈ 2187 × 0.0929 ≈ ≈203 kg FM200
(Calculated with the surface Class A value of 7.9%, the same volume would give ≈188 kg — note that the class selection directly drives the agent quantity.)
As temperature falls, specific volume decreases and more agent is required for the same volume; the lowest design temperature of the space is therefore used.
Altitude above sea level and the atmospheric correction factor
The formula above gives the agent mass for sea-level atmospheric pressure. The correction is agent-independent and applies only above ≈1,000 m (ISO 14520-1 cl. 7.7); the agent mass is multiplied by the Table 5 factor. For example, the server room above draws no correction in Ankara (≈900 m, ≈203 kg); at a 1,500 m site it becomes 203 × 0.830 ≈ ≈169 kg FM200. For the full factor table and rationale, see the shared calculation rules in our Gas Suppression: Design and Agent Selection article.
What may be deducted from the volume?
Only permanent structural elements (reinforced-concrete columns/beams) may be deducted from the gross volume; movable equipment — cabinets, panels, server racks, shelving, machinery — is not deducted, because if removed the free volume grows and the concentration falls below the design value. The calculation is always based on the largest (safest) free volume, as if the equipment were not there. For detail, see the shared calculation rules in our pillar article.
Suspended ceilings and raised floors
Server rooms and electrical spaces usually include a suspended ceiling and a raised floor. If these voids are ignored in design, the system leaves genuinely unprotected volumes. The approach depends on the nature of the void:
- If the void contains a fuel load (cable trays, power/data cabling, interconnections) or is part of the airflow path, that void is included in the protected volume. Two methods are used in practice:
- Integrated (combined) volume: if the suspended ceiling/floor is not gas-tight and the void freely exchanges air with the room, the void is combined with the room volume; the total is calculated as a single volume, with a separate nozzle at each level (above ceiling, room, below floor) to achieve homogeneous concentration.
- Separate zone (compartment): if the void is isolated as a gas-tight compartment, it is treated as a separate protected volume with its own nozzle line and added to the required agent quantity.
- If the void is entirely empty, sealed and holds no fuel load, it may be excluded from protection — but this exception is accepted only after site verification.
In short: the space above a suspended ceiling and below a raised floor are protected volumes by default; their gas-tightness and fuel load determine whether they are solved as integrated or separate zones. In both cases these volumes are added to the agent quantity calculation and the nozzle layout is arranged accordingly.
System devices and damper automation
The core logic of the contact-output pressure gauge, the pressure switch and the ventilation/damper automation is common to all gas systems; for the detailed explanation and the correct discharge sequence, see the shared equipment and automation section of our Gas Suppression: Design and Agent Selection article. In brief: the pressure gauge monitors cylinder pressure and verifies the system is ready to fire; the pressure switch senses discharge and triggers the alarm/HVAC shutdown/damper closure; the dampers are closed before discharge and kept closed throughout the hold time (≈10 min).
FM200-specific points: discharge completes in ≤10 seconds (nozzles and pipe hydraulics are sized accordingly); the post-hold purge ventilation matters because it exhausts residual agent along with any decomposition products (HF, etc.). The overpressure relief damper that balances discharge overpressure is adequate at a standard size for halocarbons.
Design and application: what to watch for
- Enclosure integrity and door-fan test: the hold time is measured and verified by a door-fan test. A correct calculation on paper fails in a leaking enclosure; cable penetrations, door undercuts and duct gaps must be sealed.
- Net free volume: deduct only columns/beams; do not deduct equipment (see above).
- Altitude correction: applied only above ≈1,000 m (ISO 14520 cl. 7.7); below that the factor is 1.00. Above 1,000 m use the Table 5 factor (e.g. 1,500 m → 0.830).
- Voids: suspended ceiling and raised floor are included in the volume; choose integrated or separate-zone solution.
- NOAEL margin: in occupied spaces keep design concentration below NOAEL (9%).
- ≤10 s discharge: size nozzles and pipe hydraulics to achieve it.
- Nozzle coverage limits: each nozzle has area and height limits; the manifold and nozzle line are engineered to the room geometry for homogeneous distribution.
- Overpressure relief damper: correctly sized for the discharge overpressure.
- Device supervision: monitor agent loss continuously via the contact-output gauge; confirm discharge via the pressure switch.
- Scenario integration: detection → alarm/delay → HVAC/dampers → discharge → hold → purge, built as a single automatic scenario; define gas/power cut-off and BMS integration.
- Periodic maintenance: cylinder weighing/pressure checks, hose and valve tests performed regularly; see our fire system periodic maintenance article for detail.
Summary
Success with an FM200 system is less about choosing the right agent and more about calculating and integrating it correctly: determining the net free volume accurately (deducting only columns/beams), including suspended-ceiling and raised-floor voids in the volume, protecting occupants against the NOAEL/LOAEL thresholds, positioning the contact-output gauge and the pressure switch correctly, and closing ventilation/dampers before discharge and keeping them closed throughout the hold time. For data centers — where these decisions are applied most intensively — see our Data Center Fire Safety article; for FM200 design and volume calculation specific to your facility, reach us for a free site survey within Ankara.
This content is for information only. Binding calculation and design for your facility require project-based work with a fire engineer under ISO 14520 / NFPA 2001.
© 2026 A-Pro Mühendislik. This is original technical content produced by A-Pro Engineering; all rights reserved. Copying, reproducing or republishing it in whole or in part without attribution and permission is prohibited.
Frequently asked questions
What can be deducted from the enclosure volume in an FM200 calculation?+
Only the volume of permanent (non-removable) structural elements — impermeable, fixed building components such as reinforced-concrete columns and beams — may be deducted from the gross volume. Movable equipment such as cabinets, panels, server racks, shelving and machinery is NOT deducted, because it may later be relocated or removed; if removed, the free volume grows and the gas concentration drops below the design value. The calculation is therefore always based on the largest (safest) free volume, as if the equipment were not there.
What do NOAEL and LOAEL mean?+
NOAEL (No Observed Adverse Effect Level) is the highest gas concentration that produces no observable adverse physiological effect in humans; for FM200 it is 9%. LOAEL (Lowest Observed Adverse Effect Level) is the lowest concentration at which an adverse effect appears; for FM200 it is 10.5%. In occupied spaces the design concentration is kept below NOAEL with a safety margin; for FM200 both the surface Class A value (7.9%) and the high-hazard value (8.5%) are below the 9% NOAEL. In high-hazard spaces such as data centers (8.5%) the margin is tight, so egress and delay time are critical.
What is the difference between a contact-output pressure gauge and a pressure switch?+
The contact-output pressure gauge (supervisory pressure switch with dial) sits on the cylinder and continuously monitors agent pressure; if pressure falls below threshold (leak / agent loss) it sends a trouble/supervisory signal to the fire panel — it verifies the system is charged and ready. The pressure switch is on the discharge/manifold line and senses actual flow pressure when the agent truly discharges, sending a confirmed 'gas discharged' signal that triggers the 'GAS RELEASED' warning signs, ventilation shutdown and damper closure.
How are ventilation and dampers controlled when FM200 discharges?+
Immediately before discharge, all HVAC serving the space must stop and every supply, exhaust and recirculation damper must close; otherwise the agent is carried out and the hold time cannot be achieved. Sequence: cross-zone detection → alarm + delay → stop HVAC + close dampers → discharge → keep closed throughout the hold time. A separate overpressure relief damper momentarily opens and re-closes to relieve the discharge overpressure. After the hold time and confirmed extinguishment, the space is purged by a separate ventilation cycle before re-entry.
Why is FM200 discharged in 10 seconds or less?+
FM200 is a chemical agent that produces some decomposition products such as hydrogen fluoride (HF) at high temperature. Completing discharge in ≤10 seconds both reaches design concentration quickly to extinguish early and shortens the agent's exposure to flame, minimising decomposition-product formation. The 10-second rule is therefore standard for both performance and safety (ISO 14520 / NFPA 2001).
How does the FM200 design concentration change with hazard class?+
In Turkey the basis is ISO 14520 (TS ISO 14520), which applies a ×1.3 safety factor to the extinguishing concentration and defines three classes. For FM200 (HFC-227ea) per ISO 14520-9: Class A – Surface = 7.9% (de-energised, low-cable-load spaces, archive/paper store); Class A – High hazard = 8.5% (data center/server/telecom/MDF — equipment energised and load > 5 kW; dense cable load; energised switchgear/UPS); Class B – Flammable liquid = 9.0% (generator/fuel room, oil-filled transformer, paint store). Important: because clean agent is chosen precisely to protect energised equipment, data centers are almost always Class A – High hazard (condition 4: energised + > 5 kW). NFPA 2001's separate 'Class C' does not exist in ISO; in content it maps into this class.
When is a space treated as Class A – High hazard?+
Per ISO 14520-1 clause 7.5.1.3 (aligned with NFPA 2001-2012 A.5.4.2.2), if any of these conditions exists the space is treated as Class A – High hazard (8.5%) rather than surface Class A: (1) cable bundle diameter > 100 mm (4 in.); (2) cable tray fill density > 20% of the tray cross-section; (3) horizontal/vertical cable-tray stacks < 250 mm (10 in.) apart; (4) equipment energised during extinguishment with collective power > 5 kW. The first three indicate a dense cable load, the fourth energised equipment; cable galleries and switchgear/UPS rooms that cannot be de-energised are typical examples.
How does altitude above sea level affect the agent quantity?+
ISO 14520-1 (clause 7.7) requires the atmospheric correction only when the ambient pressure varies by more than 11% from sea level — roughly above 1,000 m. So up to ≈1,000 m the factor is taken as 1.00 with no extra multiplier; above 1,000 m the agent mass is multiplied by the Table 5 factor (1,000 m → 0.885; 1,500 m → 0.830; 2,000 m → 0.785). For example, Ankara (≈900 m) is below the 1,000 m threshold so no correction applies (≈203 kg); at a 1,500 m site the same system becomes 203 × 0.830 ≈ 169 kg.
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