Hazards of Chemicals and Gases
Proper storage and handling of containers avoids many possible incidents. Hazards resulting
from the rupture of a cylinder or other vessel containing gas at high pressure are protected
against by careful and secure handling of containers at all times. For example, cylinders should
never be struck nor allowed to fall, because if the cylinder is charged to a high pressure and the
cylinder valve is broken off, it could become a projectile. Cylinders should not be dragged or
rolled across the floor; they should be moved by a hand truck. Also, when they are upright on
a hand truck, floor, or vehicle, they should be chained securely to keep them from falling over.
Moreover, cylinders should not be heated to the point at which any part of their outside surface
exceeds a temperature of 125 F, and they should never be heated with a torch or other open
flame. Similar precautions are taken with larger shipping and storage containers. Initial
protection against the possibility of vessel rupture is provided by the demanding requirements
and recommendations that compressed gas containers fulfill in their construction, testing and
Most cryogenic liquids are colorless, odorless, and tasteless when vaporized to a gas. As liquids,
most have no color (except liquid oxygen which is light blue). However, whenever the cold
liquid and vapor are exposed to the atmosphere a warning appears. As the boil-off gases
condense moisture in the air, a fog forms that extends over an area larger than the vaporizing
gas. Many cryogenic liquids are inert gases, and may inert an enclosed space. Inert gases will
not support life.
Both the liquid and its boil-off vapor can rapidly freeze human tissue and can cause many
common materials such as carbon steel, plastic, and rubber to become brittle or fracture under
stress. Liquids in containers and piping at temperatures at or below the boiling point of liquified
air (-318 F) can cause the surrounding air to condense to a liquid.
Extremely cold liquified gases (helium, hydrogen, and neon) can even solidify air or other gases
to which they are directly exposed. In some cases, plugs of ice or foreign material will develop
in cryogenic container vents and openings and cause the vessel to rupture. If a plug forms,
contact the supplier immediately. Do not attempt to remove the plug; move the vessel to a
All cryogenic liquids produce large volumes of gas when they vaporize. For example, 1 volume
of saturated liquid nitrogen at 1 atmosphere vaporizes to 696.5 volumes of nitrogen gas at room
temperature at 1 atmosphere.
When vaporized in a sealed container, cryogenic liquids produce enormous pressures. If 1
volume of liquid helium at 1 atmosphere is warmed to room temperature and vaporized in a
totally enclosed container, it has the potential to generate a pressure of more than 14,500 psig.
Because of this high pressure, cryogenic containers are usually protected with two pressure-relief
devices, a pressure-relief valve and a frangible (easily broken) disk.