Toxicological Effects of the Physical Agents
Authors: Sliney David H. 
Published: August 2005

The toxicological approach has been shown to have benefit when deriving human exposure limits, or threshold limit values (TLVs) for physical agents. However, some adjustments must necessarily be made to the approach followed by chemical toxicologists. Also, the philosophies relating to the control of exposure may be quite different. Concepts such as “routes of entry” must be modified. Target organs differ and dosimetric concepts vary from agent to agent.

There are over 700 chemical substances that have had TLVs assigned by the American Conference of Governmental Industrial Hygienists (ACGIH). Many other chemicals have been studied. Toxicologists, industrial hygienists, and occupational physicians are generally well trained to recognize the hazards of different classes of chemicals, their route of entry, sampling techniques, and control measures. The toxicological literature is extensive, and the ACGIH Documentation for all these substances is both extensive and widely available. However, when one approaches the several physical agents, most toxicologists, industrial hygienists, and physicians appear to feel somewhat uneasy and less than fully informed. Noise is perhaps one exception, as most of these specialists have had some exposure to the subject. Mention magnetic fields, lasers, whole‐body vibration, infrared, or other physical agents, and most health scientists must search for a book. Fortunately, there are only a few physical agents with which to be concerned. The ACGIH Physical Agents TLV Committee has identified only 16 physical agents for which TLVs could be established since that Committee was initiated in 1966. Hazard assessment, measurement and evaluation, and engineering controls for each physical agent may differ considerably. If one examines the physical agents TLVs, one is struck by the variation in the physical quantities and units to describe, measure, and assess the hazard. Indeed, rather different technologies apply to different agents. Specialists exist in each technology who are expert in assessing those hazards, but are frequently not expert in the hazards and terminology of other technologies. The detailed information relating to each physical agent is generally found in separate texts.

Industrial hygienists and occupational health professionals worldwide routinely make use of PELs, TLVs, MACs, and toxicological data for chemicals. Industrial hygienists are very familiar with the use and the special notations for different classes of chemical substances. However, when it comes to the evaluation and control of potential hazards from physical agents, the beginner is frequently astonished by the seeming complexity—with different terminologies for different human exposure limits, the different types of engineering technologies, the various restrictions, and the specialized mathematical formulas. Some occupational health professionals complain that even the TLVs and basic technical data for many physical agents are overly complex. They feel that too many specialized mathematical expressions are used and are not readily understood by the average health and safety professional. Others also question whether the exposure guidelines and controls could not be simplified or made more readable.

These concerns are understandable when one recognizes that physics, biophysics, and engineering disciplines are applied most heavily in studies of any physical agent; whereas chemistry, biochemistry, and biological disciplines are fundamental to the studies of the chemical agents. The different approaches in dealing with chemical agents also appear when one examines occupational exposure limits, such as the ACGIH TLV list. If one examines an entry in the chemical substances TLV list, a single line of print is normally sufficient to present the TLV for a single substances. With large groupings of the chemical substances, similar toxicological approaches, similar methods of analysis, and similar methods of controls can apply. Broad statements can be made about each grouping of chemical substances. By contrast, a listing for a physical agent may require several pages to present. A physical agent may act uniquely on one organ or tissues, and these vary with each physical agent. Different physical quantities and units often apply, and different spatial and time dependencies are typical for each agent. Entire books and lengthy standards have been written about each physical agent.