Working safely with cryogenic liquids 

Reyer Jochemsen

Cryogenic liquidsGas Boiling

point

(K)

Latent heat

(kJ/l)

type liq ->gas

volume ratio

N2 77 162 inert 800

He 4.2 2.6 inert 700

H2 20.4 32 explosive 600

O2 90 243 reactive 800

CO2 196 200 inert 900

Working safely

avoid contact

avoid pressure build-up

avoid rapid evaporation (suffocation, elevator)

do not breath in

use safety glasses

use insulating gloves

do not work alone (as much as possible)

Transport

only in metal vessels

not at over-pressure

careful in the elevator

only inert gases

Liquid heliumLiquid heliumWhenever one works with very low temperatures, the safety aspect should play an important roll. There are several hazards to consider.1. The fluids mentioned are extremely cold; as mentioned, helium is the coldest of all fluids. Contact with cold fluids (even cold helium gas!) causes severe frost burns.2. The extremely low temperatures of liquid helium will cause air to condense and freeze. A typical example of this is the occurrence of fluid droplets on helium evaporation pipelines; these are droplets of liquid air, so be careful.3. When working with liquid helium, keep external surfaces clean. In paragraph 2, the occurrence of droplets on the outside of pipelines is mentioned. In case of this kind of condensation, the liquid nitrogen will evaporate out of the liquefied air first, because it has a lower boiling point than oxygen. As a result an oxygen-rich fluid drips from the pipeline; when this happens, spontaneous ignition of grease and oil is not impossible. A clean work area is important.4. NEITHER helium, NOR nitrogen supports life. At high concentrations of helium gas or nitrogen gas an imminent oxygen shortage occurs.Although helium is not toxic, it may cause breathing difficulties in poorly ventilated rooms. High concentrations of helium gas can be noticed by the effect on the vocal cords.

Gasses at high pressurehigh pressure cylinders - do not drop

- use with safety cap- fix to the wall- transport on cart with chain- do not pump on pressure reducer- always close the main valve

What to do if…

there is an accident: phone reception 5678

someone gets severely frozen: phone EHBO through reception 5678

telephone number outside working hours: 4444

someone gets a frozen spot : treat like burning : lots of running water

How to obtain cryogenic liquids

Cryogenic Department (groundfloor)

Hans van Kuijk 5941

Rob van Noort

Wilfred van der Geest

http://www.physics.leidenuniv.nl/institute/cryo/command.asp

Demonstration

Let’s go