power as the separation is reduced. However, this highly nonlinear falloff of magnetic field with distance results in an insidious hazard. Objects made of ferromagnetic materials such as ordinary steel may be scarcely affected beyond a certain distance but at a slightly shorter distance may experience a significant attraction to the field. If the object is able to move still closer, the attractive force increases rapidly, and the object can become a projectile aimed at the magnet. Objects ranging from scissors, knives, wrenches, and other tools and keys to oxygen cylinders, buffing machines, and wheelchairs have been pulled from a considerable distance to the magnet itself.
Superconducting magnets use liquid nitrogen and liquid helium coolants. Thus, the hazards associated with cryogenic liquids (see section 3.E.2) are of concern, as well.
There is no epidemiological evidence that exposure to static magnetic fields results in adverse effects on human health (Persson and Stahlberg, 1989; Budinger, 1992). The health effects of electromagnetic fields remain unresolved (Hileman, 1993). The effects of electromagnetic fields on protein biosynthesis, similar to those seen in response to heat shock, and the response of cells to changes in electrical stimulation have been reported (Blank, 1983).
Among the most common injuries in laboratories are back injuries and injuries arising from broken glass and from slipping or tripping. Cuts can be minimized by the use of correct procedures (e.g., the procedure for inserting glass tubing into rubber stoppers and tubing, which is taught in introductory laboratories), through the appropriate use of protective equipment, and by careful attention to manipulation. Spills resulting from dropping chemicals not stored in protective rubber buckets or laboratory carts can be serious because the worker can fall or slip into the spilled chemical, thereby risking injury from both the fall and exposure to the chemical. Chemical spills resulting from tripping over bottles of chemicals stored on laboratory floors are part of a general pattern of bad housekeeping that can also lead to serious accidents. Wet floors around ice, dry ice, or liquid nitrogen dispensers can be slippery if the areas are not carpeted and if drops or small puddles are not wiped up as soon as they form. Attempts to retrieve 5-gallon bottles of distilled water, jars of bulk chemicals, and rarely used equipment stored on high shelves have often led to back injuries in laboratory environments. Careful planning of where to store difficult-to-handle equipment and containers (because of weight, shape, or overall size) can therefore be expected to reduce the incidence of back injuries.
Biohazards are a concern in laboratories in which microorganisms or material contaminated with them is handled. These hazards are usually present in clinical and infectious disease research laboratories, but may also be present in any laboratory in which bodily fluids or tissues of human or animal origin are handled. Occasionally, biohazards are present in testing and quality control laboratories, particularly those associated with water and sewage treatment plants and facilities involved in the production of biological products and disinfectants. Teaching laboratories may introduce low-risk infectious agents as part of a course of study in microbiology for advanced students.
A consensus code of practice for controlling biohazards, Biosafety in Microbiological and Biomedical Laboratories, was first produced by the Centers for Disease Control and Prevention and the National Institutes of Health in 1984; the third and most recent edition was published in 1993 (U.S. DHHS, 1993).
The discussion in this section provides a brief primer on the hazards arising from radioactivity. A comprehensive treatment of radiation laboratory safety is given in Shapiro (1990).
Unstable atomic nuclei eventually achieve a more stable form by emission of some type of radiation. These nuclei or isotopes are termed radioactive. The energy emitted from a decaying nucleus may be alpha, beta, or gamma particles or electromagnetic radiation gamma rays or x-rays, as discussed below. Radiation that has enough energy to ionize atoms into ions and electrons is denoted ionizing radiation. Ionizing radiation can also be produced by machines such as particle accelerators and x-ray machines.
Alpha particles are charged particles containing two protons and two neutrons and are emitted from certain heavy atoms such as uranium and thorium. An alpha particle can be stopped by a sheet of paper but is very damaging inside the body.
Beta particles are electrons emitted with very high energy from many radioisotopes. Positively charged counterparts of beta particles are called positrons. Positronic and electron emissions from radioactive atoms can be shielded by thin metal foils or one-quarter inch of plastic. Tritium (3H), phosphorus-32, and carbon-14