TAGEM, Kayseri Seed Bank and Memorial IVF clinic use liquid nitrogen (-196 C) to store seeds, DNA and embryos. 1 L LN2 expands to 700 L gas; in a closed room it displaces O2 and asphyxiates. NFPA 55 mandates MAWP, pressure relief, O2 monitor and egress marking for LN2.
LN2 Properties
- Boiling: -196 C
- Expansion: 1:700 gas
- Inert: Non-flammable
- Asphyxiant: Displaces O2
- Cryogenic burn: Skin injury
NFPA 55 Tank
- Vacuum jacketed: Double wall
- MAWP: 16 bar dewar
- PRV: MAWP x 1.1 primary
- Boil-off: 1-2 percent/day
- Outdoor preferred: Small indoor dewar
Room Ventilation
- Normal ACH: 6
- Emergency ACH: 30
- O2 alarm: 19.5 percent
- Evacuate: 17 percent
- Sensor: Floor 30 cm (N2 settles)
Personnel Protection
- Cryo gloves: High insulation
- Face shield: Splash
- Apron: Full coverage
- Training: NFPA 55 awareness
- Buddy system: No lone work
Use Cases
- TAGEM Seed Bank: 250,000 samples
- IVF clinic: 500-2,000 embryo tank
- Industry: Metallurgy, food freezing
- Chemical: Reactor inerting
- 2019 Alabama IVF: 3,500 embryos lost
LN2 with MEP Calc
MEP Calc sizes LN2 rooms at 30 ACH emergency, O2 alarm 19.5 percent, dewar MAWP 16 bar and NFPA 55 cryogenic layout.
Download MEP Calc on the App Store
Sources & Further Reading
NFPA 55, CGA P-12, ISO 21009, ASME Section VIII, OSHA 1910.146. NFPA 55 Compressed Gases and Cryogenic Fluids.