V. Lighting and Audio

Stage lighting and audio effects are an essential element of every theatrical production.  Lighting can set the tone for an entire production, while audio systems are used to enhance the voices of performers as well as music and special effects.  This section will address the primary hazards of working with stage lighting and sound systems.

• Electrical Safety
• Lighting Equipment
• Audio Equipment
• Fall Protection
• Ladders

A. Electrical Safety
Electricity is intrinsic in modern life. However, many students have never worked with electricity directly before working on stage.  To work near electricity safely, it is necessary to understand what hazards it presents, and how these hazards can be controlled.

How Shocks Occur
Electric shock occurs when the body becomes a part of an energized circuit.  The current enters the body at one point and leaves at another.  Electric shock normally occurs in one of three ways - individuals, while in contact with the ground, come in contact with:

1. Both wires of the electric circuit
2. One wire of an energized circuit and the ground
3. A metallic part that has become “hot” by contact with an energized conductor.

The metal parts of electric tools may become energized if there is a break in the insulation of the tool or machine wiring.

Severity of Shocks
The severity of the shock received when a person becomes a part of an electric circuit depends on three primary factors: the amount of current flowing through the body (measured in amperes), the path of the current through the body, and the length of time the body is in the circuit.

Effects can range from a barely perceptible tingle to immediate cardiac arrest, depending upon the type of circuit, its voltage, resistance, current, etc.  The table below shows the general relationship between the amount of current and the degree of injury.  While reading this chart, keep in mind that most electrical circuits can provide, under normal conditions, up to 20,000 milliamperes of current flow.

A severe shock can cause considerably more damage to the body than is visible.  For example, a person may suffer internal hemorrhages and destruction of tissues, nerves, and muscles.  In addition, shock is often only the beginning in a chain of events.  The final injury may well be from a fall, cuts, burns, or broken bones.

Preventing Electrical Hazards
Equipment: All fixed wiring and temporary wiring should be grounded or double-insulated.  Use UL (Underwriters Laboratory) approved equipment.  All dimmers and light boards should have a dead (non-conducting) front.

Repairs: Students should not attempt electrical repairs without proper training.  Equipment that malfunctions or causes shocks should be removed from service, clearly marked and repaired by a qualified individual.

Extension Cords: Extension cords are only designed for temporary use.  Use only three-wire heavy duty (number 16 or lower) extension cords.  Never use zip cord (number 18 wire) or other light duty cords.  Use of thin, light duty extension cords can increase the risk of fire and shock.  Make sure extension cords have adequate current capacity for the equipment being used.  Do not pull an electrical cord out of a socket by the cord.  This breaks interior wires and can cause a short and, possibly, a fire.  Inspect for frayed or split cords or plugs before use.

Electrical Cords: Electrical cords can also be a tripping hazard.  It is a good practice to route cords away from traffic areas to prevent trips and falls.

Avoid stretching or pinching cords between objects.  This can break interior wires, causing overheating which can result in a fire.

Protect temporary wiring from traffic by covering with a treadle.  Do not cover electrical cords with rugs; this can also result in a fire.

Circuit Protection Devices: Circuit protection devices are designed to automatically limit or shut off the flow of electricity in the event of a ground-fault, overload, or short circuit in the wiring system.  A ground-fault circuit interrupter, or GFCI, should be used in high risk areas such as wet locations or outdoor sites.  Portable GFCIs are available from any hardware store or safety supply catalog.

Training: Training is essential in working with lighting circuitry, dimmers and instruments.  Students should be trained before being authorized to work the control areas. See the Introduction section of this manual for more information on technical theater training.

Work Practices:  Never work alone on hazardous lighting procedures, such as hooking up panels.  Keep food and beverages out of the light control areas to prevent possible shocks and damage to the circuitry.

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B. Lighting Equipment

Student-run theater spaces use standard size lamps and dimmers as shown below.

 

Lamps
Fresnels	BTL 500W
	BTN 750W
	BTR 1000W
Ellipsoidals (ERS)	FEL 1000W
	EHD 500W
	EHG 750W
Source 4	HPL 575W
Dimmers
	1.2 kilowatt (1200W maximum)
	2.4 kilowatt (2400W maximum)

Several methods exist for changing the color of light projected, most commonly, the placement of color media, such as gels, tinted glass, or dichroic filters, in front of the instrument.  Several companies sell color media and only those materials intended for such use should be employed.  Common materials may not withstand the intense heat and light of stage lighting and may be a fire hazard.

Projected light patterns can be achieved by placing a pattern, template or gobo in a holder and inserting it into the slot at the gate of an ellipsoidal.  Many of the same companies that sell color media also sell a wide range of off-the-shelf patterns.  Short lived custom patterns can be cut out of several layers of black aluminum foil (commonly known as the trade name Cinefoil) using a razor blade.  For the ETC SourceFour ellipsoidals (due to their lower gate temperature), short lived custom patterns can also be cut from aluminum foil oven liner trays cut to holder size.

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C. Audio Equipment
Just as dimmers must not be overloaded with too many lamps, power amplifiers must not be overloaded with too much load.  Power ratings for amplifiers is usually specified in load capacity, while speakers (or other loads) are assigned an impedance (typically 4 or 8 ohms).  Damage to an amplifier can occur if it is not rated for the load being driven.

In an audio system, all devices should be connected to the same ground at the same point.  This helps eliminate ground loops, a problem caused by different ground levels on different circuits.  The problem usually manifests itself as hum in the audio system, but can result in electrical shocks.  For this reason, the amplifiers, sound board, and all other audio equipment need to be grounded at the same point.  Additionally, never connect audio equipment to the same circuit as lighting equipment.  Disregarding this recommendation can result in spurious noise in the audio system and damage to sensitive audio equipment. (WPI Technical Theatre Handbook, Stephen Scott Richardson)

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D. Fall Protection
The procedure for hanging and/or focusing lights may require the need for work on catwalks, scaffolding or work directly on the lighting grid.

1. Catwalks: Catwalks are equipped with railings built to specific regulations to protect from falls.  Catwalk railings should not be removed unless some other form of fall protection is employed
2. Scaffolding: For theatrical work, the OSHA standard 29 CFR 1910.28, Safety Requirements for Scaffolding, applies strict requirements for scaffolding use.  The erection, securing and dismantling of any type of scaffolding must be overseen by a trained, "competent person".  Scaffolding training is available by contacting Greg Cantrell at 8-5849.
3. Lighting Grid: Personal fall arrest systems are required when work must take place directly on the lighting grid.  Personal fall arrest systems include, at a minimum, a harness, lifeline and tie-off point.  Design or implementation of a fall arrest system should be completed by an experience professional with knowledge of structural engineering.

Empty all pockets before hanging lights.  Crew members should make sure that nothing on their person could fall to the stage.  Secure all tools with safety lines.  For more information on Fall Protection, please see the University Health & Safety Guide.

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E. Ladders
Portable ladders should be inspected at frequent, regular intervals and maintained in good condition free from oil, grease, or other slippery materials.  Defective ladders should be removed from service until repaired.  Those that cannot be repaired should be destroyed.

Ladders should always be placed on stable bases and, whenever possible, should be secured near the top and at the bottom.  Boxes, barrels, or other unstable surfaces should never be used to extend the reach of a ladder.

Environmental Health and Safety (EHS) has written a Portable Ladder Advisory for all university ladder users.  It includes a ladder inspection checklist which is helpful before each ladder use.

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