Most stages today require sprinkler systems. Underhung
rigging simply means that the blocks (sheaves or pulleys) through which
the cables and / or ropes run are mounted to the bottom flange of their
supporting beams. On any rigged stage the pipe battens supporting curtains,
lights, and rigging are moved vertically – often by crew members
who have less than full knowledge of or concern for the facility. This
is why we need to install sprinkler systems in such a manner as to
provide maximum protection to the sprinkler pipes and heads themselves
by installing them WITHIN the dimensions of the supporting steel.
Supporting steel members – whether roof beams / joists or gridiron
systems – automatically provide a well protected space into which
sprinkler runs may be placed. The major supporting steel will run parallel
to the center line of the auditorium / stage.
On any stage the area most tightly packed with curtains and rigging
is the first four feet closest to the audience. It is for this reason
that the main feed line to the system must be provided at the upstage
(rear) corner of the stage and opposite the side on which the vertical
stage rigging is run. This vertical main needs to be run to a point just
above the gridiron floor if there is one, and/or just below the bottom
edge of the roof beams.
From here a horizontal main should run across
the back wall of the stage (one at each level if there is a gridiron)
and then individual smaller runs to the heads made perpendicular to
the back wall each 10’.
Since support members are designed 10’ o.c. today the logical head
placement is half-way between the steel beams. These smaller runs need
to be placed so that the runs and sprinkler heads themselves are above
the level of the bottom part of the steel rigging support members. This
will protect the pipes and heads from mechanical damage by moving pipes
A gridiron is a steel “platform” which is provided to allow
installers and stagehands to work with lights and rigging above the stage
area and to add or alter rigging. Any point on the grid may be used at
any time for a production. The standard grid floor is made of 3” channels,
toes down, spaced 3” apart and has 10” wide “sheave
wells” each 10’.
Heads, which by code must be below the gridiron floor, can be easily
installed by laying the smaller runs between the channels which make
up the gridiron floor and placing the heads on stems to drop below the
grid yet above the bottom edge of the floor support steel. This will
make the installation simple, efficient, and will leave the grid floor
clear for movement of personnel and equipment. The smaller runs must
NEVER be attached to the rigging support beams or within a sheave well.
While original budgets often limit the amount of equipment which can
be initially installed, stages are designed to provide the capability
of placing a set of lines (moving pipe) every six or eight inches from
the audience to the back wall of the stage. This leaves little space
for clearances and less for error.
The other feeds on the stage; above lock rail, head block beams, etc.
also have space limitations and need to be checked carefully prior to
installation so they do not limit the capabilities or use of the area.
In general, leave the space between the floor and underside of the steel,
from front to rear wall, and between a pair of lines halfway between
the edge of the proscenium opening and the side wall of the stage free
of any obstructions.
© William H. Lord, 2000