Chemical Hazards in the Workplace

Ronald M. Scott

• Publisher: CRC Press
• Year: 2020
• Print ISBN: 9780873711340
• eBook ISBN: 9781000724165
• Topic: Scienze biologiche
• Subtopic: Design industriale

This book introduces you to Industrial Toxicology - and is especially valuable for the engineer, scientists, or manager with responsibility - but no previous education or experience in the subject. Very "User Friendly." Text at the upper undergraduate and graduate level.

SECTION II

HAZARDS IN THE WORKPLACE

4 INHALATION TOXICOLOGY

INTRODUCTION

In Chapter 3, we considered the lung as a route of entry into the body. In the industrial setting, this is the most important such route. Consequently, control of the workplace atmosphere is the objective of the majority of industrial hygiene studies and government regulations. This chapter focuses on the nature of atmospheric contaminants.

Substances found in the workplace atmosphere are either particulate or molecular. Particulates are either (1) solids or (2) liquids whose droplets are fine enough to remain suspended in the air. Molecular impurities are either gases or vapors. Gases are substances that would normally be in the gas phase at the existing temperature and pressure. Vapors are compounds in the gas phase as a result of having evaporated from a liquid, and are normally liquids at the existing temperature and pressure.

PARTICULATE MATERIALS

Airborne particulates are classically subdivided into groups based on their source and character. Solid particulates, for example, may be dusts if they are produced by agricultural processing or a grinding type of operation, fumes if they arise from high temperature processing (generally metal oxides), and smokes if their source is the combustion of organic substances. Dusts are generally at the high end of the size range, perhaps from 1 to 150 μm in diameter. Fumes are smaller, running from 0.2 to 1 μm in diameter, and smokes usually have a diameter of less than 0.3 μm. Liquid particulates may be mists or fogs of water droplets condensed on smaller solid particles, or droplets of organic material, such as would result from a spraying operation.

The toxic hazard primarily relates to the chemical nature of the particulate. However, the size of the particle is also a consideration. Recall that the respiratory tract from the nasal cavity to the air sacs is lined with a sticky mucous coating over moving hairlike cilia that move the mucous toward the nose. Larger particles are more likely to collide with and stick to the mucous lining. They are quickly trapped from the inspired air and removed as the mucous is moved out of the lung. The greater penetration by smaller particles lengthens their stay in the lung and increases the chance of harm. Only particles ≤ 1 μm in size are likely to penetrate as far as the air sacs. The greatest potential for harm exists in the air sacs, because the barrier between the particle and the blood is so thin, and because trapping on mucous is absent.

Various types of damage result from particulates entering the lungs. They may stay in the lung and produce local effects such as irritation. Such irritation can cause fluid to collect in the lungs, a type of pneumonia. Some of the particulates that remain in the lung generate fibrosis, a scarring of the lung accompanied by a permanent loss of functional capacity. Pneumoconiosis is a general term used to describe the harm done by the inhalation of solids as the result of occupational exposure. Symptoms include shortness of breath (dyspnea), chest pains, fatigue on exertion, and shortage of oxygen (cyanosis). Substances also may transfer from the lung into the bloodstream, traveling to organs that may then be damaged, such as the brain, liver, or kidney.

Specific Examples of Hazardous Particulates

Asbestos

Asbestosis, a lung disease caused by inhalation of asbestos fibers, is perhaps the most publicized of the lung fibrosis diseases. Most asbestos is mined in Canada. What we term asbestos is actually a number of different mineral materials which share the property of being able to form the familiar fibrous product. They are silicate compounds of calcium, sodium, iron, chromium, nickel, or magnesium. All varieties of asbestos do not present the same degree of hazard.

The long, thin fibers lodge in the smaller subdivisions of the air passages, causing irritation and edema. Continued exposure leads to permanent scarring of the lung and a resulting loss of lung capacity. Victims often have a cough, and lung infections are very common. As if all this were not enough, some types of asbestos are carcinogenic. Bronchial carcinoma (malignant mesothelioma) occurs in association with asbestos exposure. The type of asbestos called crocidolite is a particularly potent causative agent for malignant mesothelioma. Combining the inhalation of asbestos fibers with the smoking of tobacco sharply increases the risk. It is hypothesized that the surface of the fiber, as it lies embedded in the lung, serves to collect and concentrate carcinogens from the tobacco smoke.

Asbestos has found a broad range of applications largely based on its fibrous character and resistance to high temperatures. These include pipe insulation, floor tile, roofing shingles, cement, clutch pads, brake linings, wall board and plaster, and heat- and fire-resistant garments. It has been used in factories for insulation of steam pipes and boilers, as an air filter medium, in board form for partitions, as fireproofing on beams, and as insulation under the roof to prevent heat loss. Although care is taken in new installations not to use asbestos in a hazardous fashion, many older facilities have asbestos present in locations such that workers are at risk of exposure. Particular care must be exercised in removal of old asbestos from such sites; the hiring of an expert with the proper equipment and experience is wise.

Silica

Silicosis is a fibrosis of the lungs caused by silica. Victims of silicosis have symptoms much like those of asbestosis victims. In both these problems, it is characteristic that the symptoms develop slowly and may therefore be missed. If the victim is a smoker, the symptoms may be misinterpreted as being the result of the use of tobacco. As with asbestosis, infections of the lung are common, but silica does not cause cancer. Silicosis may result from the inhalation of any uncombined form of silicon dioxide. Grinding with silica abrasives, sandblasting, or working with sand in a foundry are possible industrial exposures, while sandstone quarrying or hard rock mining also provide serious occupational contact.

Talc

Talc is hydrated magnesium silicate, and is usually found in association with deposits of dolomite. It is a component of tile, paper, and paint, and is used as a lubricating powder with rubber products such as tires and gloves or as talcum powder. It does not cause the degree of fibrosis that we see with asbestos, but it is a cause of pneumoconiosis.

Mica

The mineral form of mica is called musco vite. It is found as plates which separate into thin sheets, or as a powdery product. It serves well as a heat or electrical insulator, so it is used in electrical devices and appliances. The ground material is added to roofing, and it has served as a mold release agent in the rubber industry. It also is responsible for pneumoconiosis.

Fiberglass

Fiberglass or glass wool is simply very long, thin fibers of glass. It is used as insulation and as a reinforcing material in plastics. Tiny fragments of glass wool carried as a dust in the atmosphere can enter the respiratory tract and cause irritation, much as skin contact with glass wool can cause skin irritation.

Metals and Metal Oxides

Metals and their compounds may appear in the workplace in particulate form as the result of grinding, sawing, milling, or otherwise shaping metal parts. Any time metal is melted or formed at high temperatures, metal oxide fumes may be released. Several of these fumes are irritating or damaging to the lungs. A set of symptoms very much like influenza is encountered, termed metal fume fever. These problems are discussed in more detail in Chapter 6.

Coal

The mining of coal has caused a great deal of lung damage over the years. Coal dust deposited in the lungs leads to breathlessness, and in more extreme cases to emphysema and fibrosis. The introduction of wet drilling techniques to minimize dust production was a major advance in reducing the magnitude of the problem.

Other Dusts

Not all dusts are as damaging as those already presented. When deposition in the lung does not cause inflammation or fibrosis, health problems are significantly reduced. For example, calcium carbonate (limestone or marble) and calcium sulfate (gypsum) dusts are not as threatening. Similarly, the iron oxide fume that welders encounter is not as damaging as many metal oxides. However, welders need to take precautions because many of the items being welded, as well as welding rods themselves, include more dangerous metals in their composition.

Another dangerous class of dusts are the natural product particulates. An example is the dust arising from cotton in the cour...

Table of contents

• Cover
• Title Page
• Copyright Page
• Preface
• Table of Contents
• SECTION I: BASIC TOXICOLOGY
• SECTION II: HAZARDS IN THE WORKPLACE
• SECTION III: REGULATION AND PROTECTION
• Glossary
• Appendices
• Index