Industrial hygienists know that variability is the key to the measurement and interpretation of workers' exposures. If exposures did not vary, exposure assessment could be limited to a single measurement, the results of which could be acted upon, and the matter filed away as something of no further concern. We know, however, that exposures change, and change is characteristic of the science and practice of our profession as well. We must be alert to recognize new hazards, we must continue to evaluate new and changing stresses, and we must evaluate performance of exposure controls and from time to time upgrade them. These volumes represent the theory and practice of industrial hygiene as they are understood by their chapter authors at the time of their writing. But, as observed by the Greek philosopher Heracleitus about 2500 years ago, “There is nothing permanent except change.” Improvements and changes in theory and practice of industrial hygiene take place continuously and are generally reported in the professional literature. Industrial hygienists, the practitioners, the teachers, and the managers must stay abreast of the professional literature. Furthermore, when an industrial hygienist develops new knowledge, he/she has what almost amounts to an ethical obligation to share it with others in the profession.
One cannot ponder the rapid changes and advancements made in recent decades in science and technology, and in our own profession as well, without wondering at what the next two or three decades will bring. Developments in computer technology, information processing, and exchange and communications have greatly influenced workplaces and the general conduct of commerce and business in the past one or two decades. It has also changed the way we now practice the purposes of industrial hygiene. These changes have accelerated. The possibility for continuously monitoring and computer storage of exposures of individual workers is a reality. World population continues to increase geometrically and is expected to be about eight billion in the year 2025; with improvements in preventive health care, there will be an increasingly older population. Genetic engineering and highly effective pesticides are already improving yields of agricultural commodities; if all goes well in this area, feeding the expanding human population may not be a limiting factor. Globalization of manufacturing and commerce has reduced manufacturing employment in the United States and in Europe, and expanded opportunities for populations in some developing nations. The United States and other developed nations are on their way to becoming world centers of information and innovation.
How will all of this affect the future practice of industrial hygiene? In the Preface to the fourth edition of Patty's, George and Florence Clayton suggested that the future of industrial hygiene is limited only by the narrowness of vision of its practitioners.
I have relied extensively on the well‐written Preface by Robert Harris, Editor of the fifth edition of Patty's Industrial Hygiene. In it I saw a sweeping, but still succinct, review not only of Patty's publications but also of the practice of industrial hygiene itself. His writing is as timely in 2021 as it was 20 years ago.
Occupational and environmental hygiene professionals must be aware of the changes likely to take place, and to develop strategies to assure the profession's full participation in protecting the health and safety of workers and the environment of both today and tomorrow. Our participation, locally, nationally, and globally, will continue to be greatly needed in the coming years.
Barbara Cohrssen
San Francisco, California
USEFUL EQUIVALENTS AND CONVERSION FACTORS
1 kilometer = 0.6214 mile
1 meter = 3.281 feet
1 centimeter = 0.3937 inch
1 micrometer = 1/25,4000 inch = 40 micro inches = 10,000 Angstrom units
1 foot = 30.48 centimeters
1 inch = 25.40 millimeters
1 square kilometer = 0.3861 square mile (U.S.)
1 square foot = 0.0929 square meter
1 square inch = 6.452 square centimeters
1 square mile (U.S.) = 2,589,998 square meters = 640 acres
1 acre = 43,560 square feet = 4047 square meters
1 cubic meter = 35.315 cubic feet
1 cubic centimeter = 0.0610 cubic inch
1 cubic foot = 28.32 liters = 0.0283 cubic meter = 7.481 gallons (U.S.)
1 cubic inch = 16.39 cubic centimeters
1 U.S. gallon = 3,7853 liters = 231 cubic inches = 0.13368 cubic foot
1 liter = 0.9081 quart (dry), 1.057 quarts (U.S., liquid)
1 cubic foot of water = 62.43 pounds (4°C)
1 U.S. gallon of water = 8.345 pounds (4°C)
1 kilogram = 2.205 pounds
1 gram = 15.43 grains
1 pound = 453.59 grams
1 ounce (avoir.) = 28.35 grams
1 gram mole of a perfect gas 24.45 liters (at 25°C and 760 mm Hg barometric pressure)
1 atmosphere = 14.7 pounds per square inch
1 foot of water pressure = 0.4335 pound per square inch
1 inch of mercury pressure = 0.4912 pound per square inch
1 dyne per square centimeter = 0.0021 pound per square foot
1 gram‐calorie = 0.00397 Btu
1 Btu = 778 foot‐pounds
1 Btu per minute = 12.96 foot‐pounds per second
1 hp = 0.707 Btu per second = 550 foot‐pounds per second
1 centimeter per second = 1.97 feet per minute = 0.0224 mile per hour
1 footcandle = 1 lumen incident per square foot = 10.764 lumens incident per square meter
1 grain per cubic foot = 2.29 grams per cubic meter
1 milligram per cubic meter = 0.000437 grain per cubic foot
To convert degrees Celsius to degrees Fahrenheit: °C (9/5) + 32 = °F
To convert degrees Fahrenheit to degrees Celsius: (5/9) (°F − 32) = °C
For solutes in water: 1 mg/liter 1 ppm (by weight)
Atmospheric contamination: 1 mg/liter 1 oz/1000 cu ft (approx)
For gases or vapors in air at 25°C and 760 mm Hg pressure:
To convert mg/liter to ppm (by volume): mg/liter (24,450/mol. wt.) = ppm
To convert ppm to mg/liter: ppm (mol. wt./24,450) = mg/liter
Factors for conversion of some units
Mg/L × 28.32 = Mg/cubic foot
Mg/L × 1000 = Mg /cubic meter
Mg/cubic foot × 35.314 = Mg/cubic meter
Mg/cubic meter × 0.2832 = Mg/cubic foot
CONVERSION TABLE FOR GASES AND VAPORSa (Milligrams per liter to parts per million, and vice versa; 25°C and 760 mm Hg barometric pressure)
| Molecular Weight | 1 mg/liter ppm | 1 ppm mg/liter | Molecular Weight | 1 mg/liter ppm | 1 ppm mg/liter | Molecular Weight | 1 mg/liter ppm | 1 ppm mg/liter |
| 1 | 24,450 |
0.0000409
|