Safety in the Use of ChemicalsChapter 2Health and Safety Problems Caused by Chemicals |
The effects of chemicals on health depend upon a number of factors such as how they get into the body, their chemical and physical properties, how dangerous they are, the amount (dose), duration of exposure, and the personal characteristics of the individual such as age, sex, health status and susceptibility to certain chemicals. Each chemical affects human health in its own way.
Physical characteristics
The vapour pressure and boiling point of a chemical determine how much of it will be airborne. The lower the boiling point and the greater the vapour pressure, the more likelihood there is of its evaporation. Most of the volatile organic chemicals, like benzene, toluene and acetone, have high vapour pressure and low boiling points. If containers of such chemicals are left open, or if they are allowed to spread over large surfaces, they are likely to cause more breathing hazards.
The particle size of dust determines where it will be lodged in the respiratory system. Bigger particles stick in the nose and throat area, while smaller particles enter the lower parts of the respiratory tract. Most large particles get spit out or swallowed and are not usually cause for concern (except for toxic and allergic dusts).
The shape of the particle may also determine its effects on health. Some dusts (like asbestos) are more harmful because of their fibrous shape.
Chemical properties
Most mineral acids and alkalis tend to react with organic matter and water. As the human body is also composed of organic matter and contains lots of water, it also reacts with such chemicals, resulting in serious health problems.
Toxicity
The health hazards of chemicals may be quite different. One example is water, whose chemical name is hydrogen oxide (H2O). Water is essential for our lives, without it we cannot survive for long. Another chemical with similar formula is called hydrogen peroxide (H2O2). It is a very reactive chemical and would cause serious poisoning if you tried to drink it.
Some chemicals are inherently more toxic than others. Lead is an example of toxic metals. It can cause serious health problems related to the nervous system even in small doses. On the other hand iron, another metal, is required by the body and its deficiency may cause diseases like anaemia.
Dosage
It is the quantity of the chemical which usually determines the effect on our health. The doses in terms of chemical exposure are usually expressed in very small units, called ppm (parts of the chemical in a million parts of air), for most gases vapours and some aerosols. For most aerosols, the unit of dose is usually mg m-3 (milligrams of aerosol per cubic metre of air).
Length of exposure
Brief exposure to hazardous chemicals (minutes, hours, several days) is usually referred to as acute exposure. Health effects from such exposure are usually immediate and are reversible in most cases, when the intensity of exposure is not very high. Irreversible or permanent health effects, including death, may occur from acute exposure to very high concentrations of toxic chemicals.
Of more concern is repeated exposure to small doses of hazardous chemicals over long periods, referred to as chronic exposure. The health effects may not be evident for a long time, sometimes long after the exposure has stopped. Such long-term exposure is difficult to recognize because of the latency period between the exposure and the time when the health effects become evident. A deadly example of chronic exposure is that of asbestos: a large number of people continued to inhale asbestos dust for long periods before they became seriously ill.
Individual factors
There are a number of factors which vary from person to person which determine the actual health effects of exposure to chemical substances. Children and old people are more susceptible to the health hazards of chemicals. Women during pregnancy may be more susceptible to certain chemicals, and some chemicals have adverse health effects on the foetus. Body weight, metabolic rate, drinking and smoking habits also make certain people more prone to health damage from exposure to chemicals. Again, an example is exposure to asbestos. If a person is a smoker and is also exposed to asbestos fibres, the risk of having lung cancer increases 40 times more than the risk of exposure to asbestos fibres alone. Some chemicals may cause allergic symptoms in certain people, while others may use them for long periods without adverse effect.
Chemical health hazards
| The effects of chemicals on health may range
from temporary discomfort to permanent damage. The actual effect depends on the dose and toxicity of the chemical and the duration of exposure, in addition to personal factors. |
Some chemicals affect health in multiple ways. For example, benzene can cause nervous system problems and skin irritation in the short term, but in the long run it may damage the blood-forming tissues of the body and may also cause leukaemia (a form of blood cancer).
Skin problems
Corrosive chemicals like concentrated acids, alkalis and certain metal salts can cause immediate damage to the skin. Most organic solvents cause skin problems if exposure continues for long periods (from a few hours to several days) by dissolving the protective lipid layer of the skin and making the skin dry, rendering it more permeable to other chemicals. Such chemicals are labeled primary irritants.
Other chemicals cause the so-called allergic dermatoses, or conditions in which the skin becomes sensitive, and rashes and redness are caused by exposure. Some allergies, once acquired, remain with the person for a lifetime, even though the source of exposure may be removed. Once the person gets exposed to the allergic chemical in a small dose, the symptoms of the allergy return. Table 2.1 lists some commonly encountered situations and occupations in which potential skin damaging agents may be found.
Table 2.1 Some common skin damaging chemicals and activities and occupations where they might be encountered
| Type of skin damaging chemicals | Chemical nature of the chemical agent | Activities/situations where it is likely to be found |
| Primary irritants | Mineral acids
Alkaline materials
Organic solvents
Degreasing agents |
- Electro-plating
- Battery manufacture - Textile dyeing/finishing
- Textile finishing/dyeing - Metal fabrication shops
- Paintings, varnishing - Furniture polishing - Auto repair garages - Printing presses
- Metal fabrication and engineering shops - Repair shops of most industrial enterprises |
| Allergic substances | Nickel
Chromates |
- Nickel plating/polishing
- Construction and cement industry - Electroplating work |
Breathing problems
Most chemicals from the working and the natural environment enter the human body through breathing. Several of these, alone or in conjunction with other factors, cause a wide spectrum of diseases, many related to the respiratory system. These diseases range from mild irritation and headaches to asthma, scarring of the lungs and even cancer. While nuisance dust may cause only temporary discomfort and some sneezing and cough, there are some mineral dusts which, if inhaled in sufficient quantities for a long time, may cause serious respiratory disorders.
There is a whole group of respiratory diseases caused by the inhalation of different kinds of dusts, called collectively pneumoconioses. Some of these diseases like byssinosis (caused by inhalation of cotton dust and trash), silicosis (caused by inhalation of free silica) and asbestosis (caused by inhalation of asbestos fibres) have debilitating effects on the health of the affected persons.
Several of the common pollutants found in urban and work environments may cause chronic cough with spitting, usually known as chronic bronchitis. If large amounts of dust particles are inhaled for a long time, they may cause permanent damage and scarring of the lung tissue, resulting in a disorder called emphysema, leading to breathing difficulties.
A number of chemicals have sensitizing effects on the respiratory system; once a person is sensitized to them, he is prone to develop allergy symptoms whenever he comes in contact with them again. Certain chemicals like toluene diisocyanate (TDI) are strong sensitizers and can cause asthma. A list of respiratory diseases caused by chemical substances is given in Table 2.2.
Table 2.2 Some common respiratory disorders caused by exposure to chemicals
| Disease or disorder | Causative agent | Activities or occupations where one is likely to be exposed |
| Chronic bronchitis
and emphysema |
Traffic pollution
Nuisance dusts |
Living and working in areas with high dust and pollution level |
| Bronchial asthma | - Dusts from vegetable and animal products (such as flour, cereal, cakes of some oilseeds, some gums; hair, nail and excreta of animals, etc.)
- Some antibiotics like betalctamine and streptomycin - Detergents (from proteolytic enzymes) - Cyanate containing chemicals like paints, lacquers, adhesives etc. |
Farming and agro-based industries
Pharmaceutical industry Detergent making Paint manufacture, printing, spray painting, polyurethane manufacture |
| Byssinosis | Cotton dust | Textile mills (particularly in carding and bale opening sections of spinning mills) |
| Silicosis | Free silica | Silica sand quarries, foundries, glass industry |
| Asbestosis | Asbestos dust | Working with asbestos products, asbestos mining |
| Breathing difficulties and damage to respiratory system | Poisonous gases like chlorine, hydrogen sulphide, ammonia | Inhalation of large amounts of gas in cases of spills or accidents |
Problems of the nervous system
The nervous system can be affected by a number of chemical agents. Sometimes the effects may be limited to temporary headaches or dizziness or a feeling of being drugged, which goes away soon after the source of exposure is removed. Several chemicals are capable of inflicting serious damage to the nervous system; this may not become evident immediately.
Some chemicals bring about psychological and behavioural changes. Most organic solvents commonly found in homes and workplaces produce headaches or dizziness. Prolonged exposure to mercury, lead, manganese and carbon disulphide can cause toxic effects on the brain, resulting in disorientation. Various pesticides like DDT, aldrin, dieldrin, endrin and chlorinated solvents like carbon tetrachloride can produces convulsions if inhaled in sufficient quantities. Exposure to organophosphorus pesticides, tetrachloroethane and mercury may result in tremors and speech difficulties.
Some people handling organic solvents in the form of glues, paints, thinners, etc. become addicted to the smell of the solvents, which have a narcotic effect on the brain. Most toxic gases like hydrogen sulphide are also poisonous for the nervous system.
Heart problems
Many poisonous gases and chemicals, if inhaled in large quantities (acute poisoning), can result in heart failure. However, this may prove of less importance than their effects on the nervous or respiratory system. Chronic exposure to carbon monoxide, found in cigarette smoke and traffic pollution, has been known to cause cardiac problems. Other chemicals associated with heart related ailments are cobalt, cadmium, halogenated hydrocarbons, aliphatic nitrates and carbon disulphide.
Blood disorders
Blood, which is a mixture of several types of cells, chemicals and fluids, performs such vital body functions as supplying oxygen to the cells, removing waste products, and fighting diseases and invasions of the body by bacteria, viruses and external agents. There are several chemical agents which impair one or more of these functions of the blood, temporarily or sometimes permanently. Benzene, commonly found in many workplaces in its pure form as a solvent or as an ingredient of gasoline, thinners and paints, damages the bone marrow, where blood cells are formed. It has also been classified as a carcinogen causing leukaemia (a form of blood cancer).
Other chemicals which may cause blood-related disorders include mercury, manganese, cobalt, arsenic, aromatic amines and nitro compounds, DDT and vinyl chloride
. Carbon monoxide gas binds itself with haemoglobin, resulting in reduced oxygen supply to the cells and tissues.
Effects on the Liver
The liver is the largest internal organ of the body (it weighs some 1.5 kilos in adults), carrying out vital functions in digesting food and storing vitamins. It acts like a chemical factory, with many of the chemical reactions taking place in different compartments of the liver all the time. It is also responsible for detoxification of drugs and chemicals which enter the body through various routes. Damage to the functions of liver may result in some very serious health problems, including the build-up of toxic materials in the body. Many chemicals interfere with or damage the functions of liver. Carbon tetrachloride, used as solvent in industry and as a dry cleaning agent, can cause serious injury to the liver leading to jaundice like symptoms. Other chlorinated and nitrated organic chemicals (like chloroform, tetrachloroethane, nitrobenzene), used as degreasers and ingredients in inks and paints, can also damage the liver. Aflatoxin produced by moulds on some food products also damages the liver functions. Some drugs and narcotics including alcohol, barbiturates and paracetamol, if taken in large quantities, can cause damage to the liver cells.
Kidney problems
The main function of the kidneys is to filter out waste products from the blood and excrete them through urine. The other function is to maintain the salt and acid balance of the body (homeostasis). Several chemicals found in the working environment damage the tissues and functions of the kidney. Acute poisoning by carbon monoxide gas causes kidney failure. Many heavy metals, such as mercury, chromium, and arsenic, can injure the tissues in the kidneys. Other materials which may damage the kidney functions include oxalic acid, tartrates, ethylene glycol, carbon tetrachloride, tetrachloroethane and arsine.
Cancer
| Several chemicals have the potential to cause cancer |
Cancer is the name given to a number of diseases (over one hundred) in which the growth of cells becomes uncontrolled and disorderly, resulting in tumours or in the proliferation of cancerous cells into different parts of the body. The exact mechanism and causes of cancer are still not understood. It is thought that most cancers are caused by the interaction of physical and chemical agents with the genetic material in the cells of body.
Cancer can remain unnoticed for long periods of time and may develop long after exposure to the causative agents (called carcinogens) has ceased to exist. Some occupations and industries present a higher risk of cancer than others. Similarly, our way of life, diet and habits also play a role in increasing or decreasing the chances of having cancer. A list of industries and occupations with a particularly high risk of cancer is given in Table 2.3.
Table 2.3 Some well known types of cancer which may be caused by exposure to chemicals
| Type of cancer | Occupations/industries where likely to found | Suspected causative agent |
| Lung | - Construction, asbestos mining, insulation material, motor vehicle repair
- Uranium mining - Chromates and chromate pigments production - Arsenic-based insecticides production and packing - Coke plants, roofing, work on asphalt plants |
Asbestos
Radon Chromium Arsenic Benzo (a) pyrene |
| Liver | Vinyl chloride related work | Vinyl chloride monomer |
| Leukaemia and lymphomas (blood related cancers) | Rubber industry, tyre manufacture, shoe manufacture | Benzene |
| Bladder | - Rubber industry, gas industry
- Dye manufacture and use |
Aromatic amines
Benzidine based dyes |
| Nose and sinus | - Furniture and woodworking
- Leather industry - Nickel refining |
Hard wood dusts
Leather dust Nickel |
Problems of reproduction
Chemicals can affect fertility in men and women. Some have been known to damage the foetus; still others can cause developmental disorders in new-born babies. Pregnant women exposed to such chemicals have an increased likelihood of giving birth to malformed babies. Certain mercury compounds affect brain development in the foetus. Some metals and their compounds, such as aluminium, arsenic, cadmium, chromium, lead and nickel, have been shown in animal studies to produce birth defects.
Several organic solvents like benzene, carbon disulphide, chloroform, methylene chloride trichloroethylene, toluene and xylene have also been shown to produce birth defects in animals. Reduced sperm count in men may be caused by past exposure to chlorinated pesticides.
Fire and explosion hazards posed by chemicals
| Three things are required to start a fire and keep it burning:
|
Many chemicals and materials can catch fire or explode, causing extensive damage to life and property. An explosion is a rapid and uncontrolled release of energy and is usually but not always accompanied by loud sound, fire, mechanical shock and bright light.
Why do chemicals catch fire?
For a material to produce flames it must be in the form of gases or vapours at a certain temperature called the flash point. If an external source of ignition like a spark is provided, the material will catch fire. It is the vapours which produce flame, not the liquid or solid itself. The lower the flash point, the higher will be the risk of the material catching fire. For example the flash point of gasoline is -32C°, that of acetone is -17.8C° and that of methanol is +11C°. For a substance to continue burning without external source of ignition its temperature must be raised to its fire point, which is slightly higher than its flash point.
If heated to a certain point, called auto ignition temperature, most flammable chemicals can spontaneously ignite without an external source of ignition. Some examples of auto ignition temperatures of commonly found flammable materials are diesel oil +250C°; acetone +465C°; methane +537C°.
Too little or too much of the vapour of the flammable substance in the air would not sustain fire. The concentration of the vapour or gas must be within certain limits called explosive limits. The lower explosive limit or LEL is the minimum concentration of the vapour (usually expressed as the percentage of material in air) required to sustain a fire, while the upper explosive limit or UEL is the maximum concentration beyond which the fire cannot be sustained, as the amount of oxygen would be insufficient to continue the fire. Thus, partially filled and open containers or tanks of flammable materials create a higher risk of fire than filled or closed ones, as the fuel-to-air ratio is more likely to reach the explosive limits in partially filled containers because of evaporation.
There may be other reasons for materials to catch fire or explode. Some, like nitrocellulose (used in the paint industry), are sensitive to shaking and can rapidly explode if the containers are not handled carefully. Some materials give off flammable gases on contact with other chemicals, and the heat of reaction is usually enough to cause fire. Examples include calcium carbide, used to produce acetylene during gas welding by mixing it with water. If not carefully handled, the reaction can cause fires and explosions.
Alkali metals on contact with water release hydrogen, which may catch fire. If some materials like oil soaked rags are thrown in a heap, the heat from the sun or the oxidation may produce sufficient heat to ignite the material. Some materials like bags of ammonium nitrate have been known to catch fire or explode when they were piled high and the heat produced due to the pressure was enough to ignite the material.
Many materials which ordinarily may not even catch fire will explode if they are present in the air in a finely particled form and the right temperature and source of ignition are provided. Such an explosion is called dust explosion and usually has devastating consequences. Some examples of the industries using materials which may result in dust explosions are given in Table 2.4
Table 2.4 Industrial operations with dust explosion hazards
| Industry | Agents likely to cause dust explosion |
| Flour mills | Grain and flour dust |
| Woodworking | Wood dust from sanding machines |
| Textile industry | Cotton dust |
| Paper and pulp industry | Cellulosic materials |
| Grain/foodstuffs storage silos | Grain dust from wheat, rice, soybeans, coffee, tea, spices, etc. |
| Coal mines | Coal dust |
Sources of heat and ignition
A number of sources may result in fires and explosions:
Open flames such as those from lighters, burners, matches and welding torches are the most common sources of ignition and are known to cause the most fires in households and industry.
Radiation in the form of sunlight or coming from hot surfaces may provide enough heat to start fires.
Sparks from various sources like switching on or off electric appliances, removing plugs, static electricity produced during rubbing of two dissimilar surfaces like combing hair, walking with plastic or rubber shoes, pouring certain liquids, chemical reactions, lightening, incandescent materials, naked light bulbs and so on.
The role of oxygen
The burning process is basically a chemical reaction between oxygen and the burning material. Such reactions, if they take place at a slower and more orderly fashion, are called oxidation. We digest our foods in this way, and iron rusts through oxidation. In fire, however, oxidation takes place very rapidly and in a disorderly manner. For a substance to continue burning, it needs a constant supply of oxygen (15-21 percent). High concentrations of oxygen usually result in intensification of the flame but sometimes may extinguish the flame by cooling, if too little fuel is available (like blowing out a candle). Some oxidizing materials (like hydrogen peroxide, potassium permanganate, ammonium nitrate, etc.) may supply the required oxygen, and the need for external oxygen will be diminished. Such materials should never be stored near flammable materials.
Devastation caused by an explosion in a factory, where gasoline was used as a solvent. The spark produced when a blower was turned off caused the explosion.
Exercise
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