Cryogenics safety Kenny Jensen Zettl Group Safety Talk

Cryogenics safety Kenny Jensen Zettl Group Safety Talk 1/25/07 9/17/2021 Zettl group meeting 1

Hazards • • • Cold contact burns Asphyxiation Pressure build-up and explosion Oxygen enrichment and explosion Heavy dewars 9/17/2021 Zettl group meeting 2

Cold contact burns • Wear appropriate eyewear – Safety goggles when pouring – Face shield for pressurized systems • Wear loose-fitting gloves • Contact with cold metal surfaces is the most dangerous 9/17/2021 Zettl group meeting 3

Asphyxiation • Don’t use cryogens in unventilated spaces • Large liquid to gas expansion ratio (1: 800) – 5 m x 5 m room = 125000 L would only require 150 L of cryogenic fluid • Cold N 2 and He are heavier than air – Watch out for low spaces like STM pit • Don’t use elevators for small dewars • Take a separate elevator for large dewars 9/17/2021 Zettl group meeting 4

Pressure build-up • Independent pressure relief devices for each component that can be isolated by valves and each closed space • Keep valves closed on LHe dewar to prevent creation of ice plugs • Only pressurize LHe dewars with He! 9/17/2021 Zettl group meeting 5

Removing an ice plug • Direct a flow of room temperature He gas (not any other gas!) onto the plug • Find a suitable length Copper rod, affix a stop point so it does not drop all the way into the dewar, contact ice plug. – Only use this technique if there is little pressure build-up 9/17/2021 Zettl group meeting 6

Oxygen enrichment • Cryogens can condense Oxygen from the atmosphere • Don’t use open flames around cryogens 9/17/2021 Zettl group meeting 7