Document akEma1N4kNRpeDpkYa09YDnN

Sampling techniques What must be measured and evaluated in industrial hygiene sampling is usually the dosage the worker receives--the amount of toxic material he takes into his body Dura tion of exposure and concentration and type of material are important For the concentra tion measurement, a test can be made on the air in the worker's breathing zone In some cases, the measuring instrument can be at tached directly on the worker and he can carry it throughout the working day (this is done with a film badge for measunng radiation ex posure) Relatively few samplers are avail able at the present time for taking continuous samples in the breathing zone The other technique is to measure concentration in the breathing zone over carefully selected inter vals, then average the results and weight each measurement according to the length of ex posure The result is a time-weighted aver age concentration A satisfactory average exposure measure ment during a particular time period, is affected by changes from day shift to night shift, from winter to summer, routine changes m process operations, or dailv changes m rate and direction of air movement, tem perature, or altitude Then too, will the pres ence of the sampler alter the routine of the operation in any manner? Is the contami nant soluble or insoluble m body fluids? What is its particle size distribution and in what portion of the respiratory tract is it likely to deposit? What is its chemical na ture? Organic mercury acts quite differently from mercury vapor, which, m turn, is quite distinct from mercury oxide Finally, are there limitations on the peak dose rates as there are for beryllium and some other com pounds? If the samples are collected at the right places and combined with a time study of the worker's activity, they can give a measure of the worker's intake of the toxic substance Whether direct-reading or laboratory tech niques are to be used is a matter of profes sional judgment The results obtained must be compared with a threshold limit value with a full knowledge of its limitation and consideration of other factors in the situation Urine assays add to the facts available for making an evaluation of exposure These, m turn, must be combined with knowledge ob tained by the physician directing an adequate medical program All this serves to empha size the basic teamwork approach of the in dustrial health program Types of measunng instruments The most numerous environmental haz ards are chemical and can be conveniently divided into (a) the particulates and (b) the gases or vapors Particulates are mixtures or dispersions of solid or liquid particles in air and include dust, smoke, nust, and similar materials Some of these are practically in soluble in body fluids, and exert their effect directly m the lungs while others are soluble and produce systemic poisoning Direct-reading instruments for the insol uble materials are difficult to make since such an instrument must count or otherwise deter mine the number of particles suspended in air, therefore some information regarding particle size is desirable Direct-reading instruments for this purpose do exist, but they are very expensive and often quite bulky These usually work on the principle of light-scattenng measuring the light scat tered at nght angles to the beam Gases and vapors can be determined more readily by direct-reading instruments since they form more homogeneous mixtures with air, and separation from the air mass is often unnecessary This group includes such com mon materials as carbon monoxide, mercury vapor, hydrogen cyanide, benzene, carbon tetrachloride, and many others A choice can be made here between direct-reading in struments or samples collected for subsequent laboratory analysis The physical hazards--heat and cold, ion izing and nonionizing radiation, and atmos pheric pressure are usually measured by direct-reading instruments In the field of ionizing radiation alone, there are literally hundreds of instruments, most of which have been developed since the early 1950's Electnca! direct-reading instruments The first general class of instruments com prises those which give a direct reading on a dial Frequently these are an electrical meter of some sort, involving electronic circuitry which requires careful maintenance to function properly Use of some instru- 1279