liquid or solid spills immediately, keeping doors and drawers closed and passageways clear of obstructions, providing step stools, ladders, and lifts to reach high areas, and walking along corridors and on stairways at a normal pace. Wet floors around ice, dry ice, or liquid nitrogen dispensers should be carpeted and paper towel dispensers made available for wiping up drops or small puddles as soon as they form.

6.C.7.4.6
Ergonomics and Lifting

Both standing and sitting in a static posture and making repeated motions have been shown to cause a wide variety of musculoskeletal complaints. Problems due to poor ergonomics include eyestrain, stiff and sore back, leg discomfort, and hand and arm injuries. Each situation needs to be evaluated individually. However, personnel who spend significant time working on video display terminals should use furniture appropriate for these tasks, proper posture, and perhaps special eyeglasses. Also, people who use the same tools and/or hand motions for extended periods of time should take breaks at appropriate intervals to help prevent injuries.

Lifting injuries are one of the more common types of injuries for laboratory workers. The weight of the item to be lifted is a factor, but it is only one of several. The shape and size of an object as well as the lifting posture and the frequency of lifting are also key factors in determining the risks of lifting. The National Institute for Occupational Safety and Health (NIOSH) has developed a guide that should be consulted to help determine lifting safety (U.S. DHHS, 1994). Personnel who are at risk for lifting injuries should receive periodic training.

6.D WORKING WITH COMPRESSED GASES

6.D.1 Compressed Gas Cylinders

Precautions are necessary for handling the various types of compressed gases, the cylinders that contain them, the regulators used to control their flow, the piping used to confine them during flow, and the vessels in which they are ultimately used. Regular inventories of cylinders and checks of their integrity with prompt disposal of those no longer in use are important. (See Chapter 4, section 4.E.4, for information on storing gas cylinders, and Chapter 5, section 5.H, for discussion of the chemical hazards of gases.)

A compressed gas is defined as a material in a container with an absolute pressure greater than 276 kilo-pascals (kPa), or 40 psi (pounds per square inch) at 21 °C or an absolute pressure greater than 717 kPa (104 psi) at 54 °C, or both, or any liquid flammable material having a Reid vapor pressure greater than 276 kPa (40 psi) at 38 °C. The Department of Transportation (DOT) has established codes that specify the materials to be used for the construction and the capacities, test procedures, and service pressures of the cylinders in which compressed gases are transported. However, regardless of the pressure rating of the cylinder, the physical state of the material within it determines the pressure of the gas. For example, liquefied gases such as propane and ammonia will exert their own vapor pressure as long as any liquid remains in the cylinder and the critical temperature is not exceeded.

Prudent procedures for the use of compressed gas cylinders in the laboratory include attention to appropriate purchase, especially selecting the smallest cylinder compatible with the need, as well as proper transportation and storage, identification of contents, handling and use, and marking and return of the empty cylinder. The practice of purchasing unreturnable lecture bottles should be discouraged if that leads to accumulation of partially filled cylinders and disposal problems. Returnable cylinders should be purchased and returned as prescribed by the manufacturer.

6.D.1.1 Identification of Contents

The contents of any compressed gas cylinder should be identified clearly so as to be easily, quickly, and completely determined by any laboratory worker. Such identification should be stenciled or stamped on the cylinder itself, or a durable label should be provided that cannot be removed from the cylinder. No compressed gas cylinder should be accepted for use that does not identify its contents legibly by name. Color coding is not a reliable means of identification; cylinder colors vary from supplier to supplier, and labels on caps have no value because many caps are interchangeable. Care in the maintenance of cylinder labels is important because unidentified compressed gas cylinders may pose a high risk and present very high disposal costs. It is good practice to provide compressed gas cylinders with tags on which the names of users and dates of use can be entered. If the labeling on a cylinder becomes unclear or an attached tag is defaced and the contents cannot be identified, the cylinder should be marked "contents unknown" and the manufacturer contacted regarding appropriate procedures.

All gas lines leading from a compressed gas supply should be labeled clearly to identify the gas, the laboratory served, and relevant emergency telephone numbers. The labels, in addition to being dated, should be color-coded to distinguish hazardous gases—that is, flammable, toxic, or corrosive substances coded with a yellow background and black letters—from inert gases, which are coded with a green background and



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