AI and HPC GPU clusters now routinely reach 50-100 kW per rack. Air cooling cannot keep up at that level, so immersion cooling — submerging the hardware in dielectric fluid — has become necessary. Novec 7100 boils at 1°C, while hydrocarbon mineral oil has a flash point around 280°C. On the fire-protection side, the rules come from NFPA 75, the standard for fire protection of information technology equipment.
Immersion Types
- Single-phase: mineral oil bath, flash point 280°C; the fluid stays liquid and is cooled externally by pumping
- Two-phase: fluids such as Novec 649 boil at 49°C and condense back on a condenser above the tank
- Synthetic hydrocarbon: the SpectraSyn family; cleaner and more stable than mineral oil
- Fluorinated fluids: Novec production is being phased out after 2025; supply will tighten
- Global warming potential (GWP): mineral oil 0, Novec family 1-300
NFPA 75 Protection
- Combustibility: the fluids used usually fall into Class IIIB (flash point above 93°C)
- Sprinkler: for ceiling protection I design with K5.6 (K80) sprinklers at 0.15 gpm/ft² (6.1 mm/min); coverage must include the tank tops
- VESDA: aspirating smoke detection with sampling pipes run between racks
- Clean agent: NFPA 2001 systems are not required for immersion tanks, but are still used in critical shared areas
- Drainage: secondary containment holding 110 percent of the tank contents is required in case of a leak
GPU Cluster Power
- H100-class GPU: typically 700 W per GPU
- Rack: rack load of 50-100 kW; at 700 W per GPU that is roughly 70-140 GPUs per rack
- Immersion tank: a typical tank circulates about 2,000 L of dielectric fluid
- Pump: we target 20-30 m³/h coolant circulation
- Coolant Distribution Unit (CDU): the heat exchanger between the tank and the external cooling tower
Risk Management
- Electrical fault: the dielectric fluid quenches arcing; fire growth risk is markedly lower than in an air-cooled rack
- Leak: a bunded floor plus liquid-detection sensors is essential
- Odor: mineral-oil systems have a characteristic smell; plan ventilation accordingly
- Biological growth: not expected in water-free dielectric fluids, but periodic samples are still taken
- Retrofit: converting an existing air-cooled hall to immersion takes about 6 months on site
AI Data Center Trends
- Largest AI training clusters: single clusters of 100,000 GPUs run on immersion cooling
- Hyperscale AI campuses: announced plans foresee around 500 MW per campus
- Turkey: hyperscale investment is accelerating at major telecom operators' data center campuses
- PUE: about 1.4 in a typical air-cooled hall, around 1.05 with immersion
- Liquid metal cooling: on the post-2030 roadmap, currently in R&D
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Download SprinkCalc on the App StoreNFPA 75, NFPA 76, ASHRAE TC 9.9, Open Compute Project, EN 50600. NFPA 75 Fire Protection of IT Equipment.