membrane disruption can occur even at relatively low acoustic intensities. Exposure to ultrasonically vibrating solids, such as an acoustic horn, can lead to rapid frictional heating and potentially severe burns.

6.C.6.2 Centrifuges

Centrifuges should be properly installed and must be operated only by trained personnel. It is important that the load be balanced each time the centrifuge is used and the lid be closed while the rotor is in motion. The disconnect switch must be working properly to shut off the equipment when the top is opened, and the manufacturer's instructions for safe operating speeds must be followed.

For flammable and/or hazardous materials, the centrifuge should be under negative pressure to a suitable exhaust system.

6.C.6.3 Electrical Instruments

Most modern electronic instruments have a cord that contains a separate ground wire for the chassis and are supplied with a suitable fuse or other overload protection. Any existing instrument that lacks these features should be modified to incorporate them. As is true for any electrical equipment, special precautions should be taken to avoid the possibility that water or other chemicals could be spilled into these instruments.

Under most circumstances, any repairs to, adjustments to, or alterations of such instruments should be made only by a qualified individual. Laboratory workers should not undertake such adjustments unless they have received certification as well as specific training for the particular instrument to be serviced. If laboratory workers do undertake repairs, the cord should always be unplugged before any disassembly begins. However, certain adjustments can be made only when the instrument is connected to a power source. Appropriate protective measures and due diligence are required when working on energized devices. Extra precautions are particularly important for instruments that incorporate high-voltage circuitry.

Many electrical instruments, such as lasers and x-ray, E-beam, radioactive, photochemical, and electrophoresis equipment, emit potentially harmful radiation, and, therefore, special precautions must be followed when they are used. This equipment should be used and serviced only by trained personnel.

(See section 6.C.1 and Chapter 5, section 5.E.)

6.C.7 Electromagnetic Radiation Hazards

Equipment found in laboratories that can produce hazardous amounts of electromagnetic radiation includes ultraviolet lamps, arc lamps, heat lamps, lasers, microwave and radio-frequency sources, and x-rays and electron beams.

6.C.7.1 Visible, Ultraviolet, and Infrared Laser Light Sources

Overexposure to direct or reflected ultraviolet light, arc lamps, and infrared sources should be minimized by sealing or enclosing sources whenever possible. Appropriately rated safety glasses, goggles, or face shields should be worn for eye protection. Long-sleeved clothing and gloves should be worn to protect arms and hands.

Control measures for the safe use of lasers have been established by the American National Standards Institute (ANSI) and presented in Safe Use of Lasers (ANSI Z136.1-1993), which describes the different types of laser hazards and the appropriate measures to control each type. Class IIIB and IV lasers should be operated only in posted laser-controlled areas. No one but the authorized operator of a laser system should ever enter a posted laser-controlled laboratory when the laser is in use.

6.C.7.2 Radio-frequency and Microwave Sources

Section 6.C.5.7 provides guidelines for the safe use of microwave ovens in the laboratory. Other devices in the laboratory can also emit harmful microwave or radio-frequency emissions. People working with these types of devices should be trained in their proper operation as well as measures to prevent exposure to harmful emissions. Shields and protective covers should be in proper position when the equipment is operating. Warning signs to protect people wearing heart pacemakers should be posted on or near these devices.

A laboratory worker removed the shield from a high-powered microwave-generating device. Fortunately, the emissions triggered the fire alarm system, prompting an evacuation of the laboratory. Had the exposure continued, the person could have suffered severe injury.

6.C.7.3 X-rays, E-beams, and Sealed Sources

X-rays and electron beams (E-beams) are used in a variety of laboratory equipment, mostly for analytical operations. The equipment is government-regulated. In most cases, registration and licensing are required. Personnel operating or working in the vicinity of these

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