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Sprinkler Systems

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 or cables.

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