(820 ILCS 245/1)
(from Ch. 48, par. 261)
When used in this Act, unless the context indicates otherwise, the
(a) "Caisson" means a wood, steel, concrete or reenforced concrete
air-tight and water-tight chamber in which it is possible for men to work
to excavate material.
(b) "Lock" means a chamber designed to facilitate the passage of men and
materials from an air pressure greater than normal, as in a compartment,
caisson or tunnel, to the ground or water level or normal air pressure.
(c) "Pressure" means gauge air pressure in pounds per square inch.
(d) "Tunnel" means a subterranean passage or chamber.
(Source: Laws 1939, p. 614.)