Module Introduction

The skin is the interface between the environment and the body, not only that there is a potential of direct contact with hazardous chemical, biological, physical, and mechanical agents, it may also be a point of entry for a number of hazardous chemicals. The eyes are the most vulnerable organs of the human body because they are easily exposed to physical, chemical, and mechanical hazards. In this Module, the focus is on the physiology of the skin and eyes, the common skin and eye hazards and occupational diseases. The skin and eye exposure control measures are also reviewed.

Learning Objectives

Upon completion of this module, you should be able to:

• Describe the basic anatomy of skin and summarize the functions and physiology of skin with respect to their significance in occupational exposure.
• Explain the causes of skin diseases and define the terms used to describe skin disorders.
• Name the four classes of occupational skin diseases; discuss the disease process and give examples of agents that cause these disorders.
• Describe the measures used to control occupational skin diseases.
• Recognize the basic process of vision and the types of hazards that can affect this process in occupational settings.
• Describe the natural protective mechanisms of the eye.
• Describe the environmental and personal control measures, and emergency response measures concerning eye hazards in workplaces.

Module Contents

This module consists of eight lessons:

• Lesson 6.1 Anatomy of the Skin
• Lesson 6.2 Physiology of the Skin
• Lesson 6.3 Definitions and Causes of Occupational Skin Disease
• Lesson 6.4 Classifying Occupational Skin Diseases
• Lesson 6.5 Protecting the Skin – Control Measures
• Lesson 6.6 Anatomy of the Eye and Hazards affecting the Eye
• Lesson 6.7 The Eye’s Natural Protective Mechanisms
• Lesson 6.8 Protecting the Eye – Control Measures
• Review
• References
• Assignments
• Quiz

 

Introduction

The skin is the largest organ of the human body with a surface area of approximately 19 square feet or 2 square metres.  It has a weight of approximately 4-5 kilograms, which represents approximately 16% of the total body weight, making the skin the body’s heaviest organ.  In relation to occupational health and safety, the skin is very important because it is usually the first part of the body that comes into contact with chemicals, physical, biological, and mechanical hazards.  Skin is also considered to be the second most common route of absorption of chemical agents.  The skin has three distinct layers of tissue: from the surface downward, they are the epidermis, the dermis, and the subcutaneous layer.  The total thickness of these three layers ranges from approximately 1/2 mm in the eyelid, to almost 5 mm in the palms of the hand and soles of the feet. Figure 6-1 shows a cross-sectional view of the skin.

A review of each of the three layers, namely the epidermis, the dermis, and the subcutaneous layer, are provided in this section.

 

Epidermis

The epidermis layer consists of layers of cell, which vary in thickness at different areas of the body.  For example, the epidermis layer of facial skin is relatively thinner than the soles of the feet.  The top layer is composed of dead cells called the stratum corneum, the keratin layer, or the horny layer.  This horny layer is the main barrier of the skin against environmental agents such as water, electrolytes, most chemicals, microorganisms, and electricity.  The term “most chemicals” is used because chemicals such as organic solvents (which are lipid-soluble) and alkalis can pass through the epidermis layer and thus, the skin.

Germinal layer

The deepest layer of the epidermis is known as the germinal layer.  In this layer, new cells are formed and are constantly pushed toward the surface to replace the stratum corneum which flakes off the body.  This characteristic regenerative or sloughing process takes about 28 days to complete.

Melanin

Among the germinal cells, there are melanocytes, or pigment-forming cells, which manufacture the pigment granules, called melanin.  The amount of melanin produced by these cells determines the skin colour.  Melanin protects the skin from ultraviolet radiation.

Note that there are no blood cells in the epidermis.  Instead, the cells are bathed in the lymph fluid.  There are also no nerve cells in the epidermis, but there are the free nerve endings in the dermis layer such as heat, cold, pain, and pressure sensors.  Since the epidermis is so thin, there is still a fine sense of touch.

 

Dermis

The dermis, also called the corium, is made up mainly of connective tissue.  It is 15 to 40 times thicker than the epidermis depending on location.  Other than the many connective tissue components, the dermis also contains hair follicles, sweat glands, oil producing sebaceous glands, the blood vessels and nerve cells.  There are some structures which extend from the dermis layer up through the epidermis layer, out into the open, such as the hair follicles.  The sebaceous oil glands, as well as the sweat glands, extend from the dermis layer, up to the surface of the epidermis layer, where they open to the outside. The dermis provides the primary protection against physical trauma, and as such can form scar tissue and maintain the integrity of the system.  The functions of the different components of dermis are discussed below.

Connective Tissue

The connective tissue in the dermis is composed of collagen elastic fibres.  This connective tissue varies in thickness over the body.  It is important in providing both flexibility and strength in the skin and support for the nerves and blood vessels passing through the dermis.

Hair Follicles

The dermis also contains hair follicles which produce hair and thereby provide protection for the outer layer in terms of mechanical shading, water loss, and are important in terms of temperature control.  It also acts as a filter for the eyes, ears and nose.  However hair follicles are also potential routes for substances to enter the body.

Sweat Glands

The dermis contains sweat glands which excrete sweat or perspiration.  There are two different types of sweat glands: eccrine and apocrine.  The eccrine glands secrete eccrine sweat that is important in terms of thermal regulation.  The eccrine sweat is a dilute aqueous solution such that evaporation of this solution from skin allows the body to cool.  The apocrine glands secrete apocrine sweat which has no known function but has some social significance.  Apocrine sweat is found in the areas of the armpits and groin.  The secretion is sterile, but upon exposure to bacteria, it will decompose and produce the typical human body odour.

Sebaceous Glands

The main function of the sebaceous glands is the production of an oil substance, sebum.  This natural skin oil provides lubrication of the hair-shaft and the horny surface layers of the skin that keeps the hair and skin soft and pliable.

Blood Vessels, Nerve Cells

Blood vessels located in the dermis layer are very important in thermal regulation.  The role of blood vessels is discussed in Lesson 6.2. The dermis also contains the majority of the various sensory receptor cells such as heat, cold, pressure, and pain.

Subcutaneous Layer

This third layer of the skin is composed of adipose tissue plus connective tissue.  The subcutaneous layer is a much less organized layer and usually has the higher content of fat than the other layers. The major feature of this layer is the presence of fat which helps to cushion and insulate the body.  Also found in the subcutaneous layer are the nerves and blood vessels, as well as the same organs found in the dermis, namely the sweat glands and hair cells.  There are also fibrous partitions of collagen, elastic, and reticulum found in the dermis, which increase the resilience of the skin and aid in the linking of the skin to underlying tissues of bones and muscles.

Physiology of the Skin

The skin has many functions.  It can be divided into three general categories:

• protection and perception,
• temperature regulation, and
• absorption  and excretion

Protection and Perception

The first and primary function is protection. Intact skin can provide the first line of defence against sunlight, moisture loss, and invasion by microorganisms and other foreign materials. It also protects against physical trauma to soft tissue and injury to vital internal organs. The skin pigment melanin is a very important component of the skin as it absorbs ultraviolet (UV) radiation from the sun.

Another function of the skin is that of perception.  With approximately 73 feet of nerves in 1 square inch of the skin, the skin perceives pain, pressure, heat and cold, with the receptors that are located in the skin.  The skin serves the important function of sensing any type of assault.

Temperature Regulation

Both blood vessels and sweat glands in the skin help the body to regulate temperature.  When we need to lose heat, vasodilation occurs.  The peripheral blood vessels expand and this allows blood to come to the surface of the skin so that heat in the blood can be dissipated to the environment.  To conserve heat, vasoconstriction takes place.  The blood vessels in the skin will constrict and not allow any blood to come to the surface area to maintain the internal temperature.  For the purpose of  thermal regulation, the eccrine sweat glands will be stimulated by the heat regulation mechanisms in the brain, resulting in the release of sweat.  Sweat flows to the skin surface where it is evaporated.  This process helps the body to loose heat.

Absorption and Excretion

Skin absorption is considered to be the second most common route by which chemicals enter the body.  There is easy penetration of the fat-soluble or lipophilic compounds, such as the organophosphates in pesticides. However there is slow penetration with the hydrophilic compounds, whose major barrier is the stratum corneum or horny layer of skin.  With respect to skin absorption, the epidermal appendages such as hair follicles and sweat glands, are an insignificant route of entry, and the total surface area used by these areas is very small, approximately 1.1%.  Therefore, the amount of chemical absorbed through the skin depends on the typical factors of concentration and contact time, and the amount of surface area involved, but most importantly the physical integrity of the epidermis or stratum corneum and the regional variation of the skin permeability.  Where the areas of the skin are thickest, the permeability is very low, but where the skin is very thin, the permeability is very high.  In addition, some molecules such as methanol, can pass through the skin by virtue of their small size.  For many gases and vapours the skin is essentially permeable.

One secondary function that the skin provides is the excretion of some toxic materials.  These toxic materials are excreted in the dead cells as they flake off, and also in the hair, and the nails.  Excretion also takes place via the sweat glands as they sweat, and the tears in the eyes.  All these can rid the body of hazardous toxic materials.  The hair, as an example, can contain such substances as cadmium and lead, which reflects exposures that have occurred.  However, it is recognized that this is not a significant route of elimination of toxicant in the body.

Introduction

In this lesson we will define certain common skin disorders and examine the various causes of occupational skin diseases.

Defining Skin Disorders

There are many types of skin disorders. The definitions of some common skin disorders are given as follows:

• Dermatitis – an inflammation of the skin from any cause. It usually involves an irritant. Therefore, dermatitis refers to an irritation of the skin and the resulting inflammation response.  Dermatitis is also called eczema.
• Dermatosis – a broader term than dermatitis.  It includes any cutaneous abnormality, such as folliculitis, which is an infection or irritation of the hair follicle caused by an obstruction by natural or industrial oil in the hair follicle.  This abnormality could be acne, pigmentary changes, or the production of nodules or tumours in the skin.
• Erythema – the reddening of the skin that occurs in the inflammation reaction as a result of increased fluid in the area.
• Edema – the swelling of tissue due to water, usually experienced in the inflammation reaction to irritation.
• Acne – dermatitis caused by oil or waxes that plug the hair follicles and sweat glands.
• Chloracne – caused by chlorinated hydrocarbons which act on the sebaceous glands in the skin and interfere with the production of oil.
• Hyperkeratinosis – refers to the hypertrophy of the horny layer of the skin.  Hypertrophy is an increase in the cell size and as a result of this we have an increase in the tissue size and a thickening of the horny layer or stratum corneum.
• Ulcers – the destruction of an area of skin or mucous membrane, usually as a result of contact with a corrosive material such as acid or base.
• Miliaria – the prickly heat rash caused by hot and humid environments where little seed-like blisters appear on the skin.

Skin disorders as a result of occupational exposures create many problems in the workplace.  However, skin problems do not only occur in the workplace.  There are also many non-occupational skin disorders. They are caused by reactions to clothing fibres, cosmetics, and cleaning agents used within and around the home.  We react to plants such as poison ivy; we may possess a variety of food allergies; some people have reactions towards jewellery and metals which come into contact with the skin.

Causes of Occupational Skin Diseases

There are four major causes of occupational skin diseases:

• Mechanical,
• Chemical,
• Physical, and
• Biological.

Mechanical 

Mechanical factors or mechanical causes are the major causes of skin disorders.  Examples are skin injuries caused by mechanical friction such as when using a shovel or putting pressure on the skin from a piece of equipment.  With repetitive motion we know that there is a friction build up and skin will react to such abrasion and develop calluses and blisters.  Persistent friction would result in broken skin and potential infection.  If the pressure is hard enough, there will be a puncture or laceration. The integrity of the skin is destroyed and again, there is an opportunity for infection.

Chemical 

Exposure to chemical agents is another major cause of occupational dermatoses or dermatitis by inducing either irritant or allergic contact sensitivity reactions.  With the large number of chemicals that are in common use and the fact that the skin is the first contact point, there is much concern regarding chemical exposures.  Examples are skin contact with acids, alkalis, metal salts, and solvents.

Physical 

Physical agents such as extreme temperatures and radiation can have adverse health effects on the skin.  The thermal factors such as exposure to extreme heat and cold can cause either burns or frostbite.  Excessive sweating due to heat exposure can lead to heat rash (miliaria).   We may also receive burns from electricity and radiation. Exposure to ultraviolet radiation, for example from the sun, could result in skin cancer.

Biological

Skin contact with biological agents such as bacteria, fungi, viruses, and parasites can cause skin disorders.  Workers in the agricultural, farming, and the health care industries are at the greatest risk of developing skin disorders from biological agents.

Given in Figure 6-2 is the statistics about the Ontario WSIB (Worker Safety Insurance Board) claims related to skin injuries over the period 1995 to 2000. The highest percentage of claims is related to skin injuries caused mainly by mechanical factors.  Out of the seven categories, “Cuts, Lacerations, Punctures” accounts for 63.3%, “Scratches, Abrasions” accounts for 19.2%, and “Burns and Scalds” accounts for 11.7% of the total number of claims.  The other four categories are minor in comparison.  These figures suggest that attention must be given to both mechanical safety aspects as well as the chemical aspects of skin injury.

Figure 6-2: Occupational Dermatological Injuries
Nature of Injury	Total Number of Claims 1995 to 2000	%
Burns or Scalds (Heat)	9,960	11.7
Cuts, Lacerations, Punctures  –  Open Wounds	53,814	63.3
Scratches, Abrasions  (Superficial Wounds)	16,363	19.2
Burns – Chemical	2,107	2.5
Burns, NEC (including friction burns)	1,141	1.3
Freezing, Frostbite and other effects of	102	0.1
Dermatitis	1,574	1.9
Total	85,061	100

Introduction

Let’s now look at the different classifications of occupational skin diseases. There are four major classes of occupational skin diseases:

• contact dermatitis,
• chemical burns,
• photodermatitis, and
• chemical acne.

Contact Dermatitis

An estimated 90% of dermatosis cases are contact dermatitis caused by direct contact of a certain skin surface with a toxic agent.  There are two types of contact dermatitis:  irritant contact dermatitis and allergic contact dermatitis. It was reported that about 80% of all cases of occupational contact dermatitis results from irritant contact and 20% from allergic contact.

Irritant Contact Dermatitis

Irritation of the skin is experienced as a result of direct contact with a toxic agent which causes chemical damage to cells, physical damage, and/or removing the protective skin oils.  These irritants are called primary irritants.  Depending on the types, concentrations, and duration of contact, these irritants can cause either acute dermatitis or cumulative dermatitis.  With acute dermatitis, the skin shows signs of erythema (reddening) and edema, which is the swelling of tissue due to increased amount of water. This will cause blistering and scaling, and a thickening of the epidermis layers.  With acute irritation, we have a reaction which is local, reversible and usually is a result of a single application with no immunological involvement.  With the typical irritation reaction we get the inflammation response.  Acids, bases and solvents can all cause a local acute irritation.

Cumulative dermatitis is a result of repeated and continued exposures to chemicals that do not in themselves cause acute irritation.  The inflammation response and the reaction is reversible.  Examples of irritants that cause cumulative dermatitis are organic solvents, metal salts, and detergents.  In examining the mechanism of irritation it is shown that the exposure affects the keratin, the fibrous tissue in the epidermis layer.  These solvents soften the keratin cells and remove them, breaking down the integrity of the epidermal layer, causing water loss and dry cracked skin, and leaving room for potential secondary infection.  A secondary mechanism in this irritation reaction is the keratin stimulants.  These are chemicals which stimulate strange growth patterns with the keratinocytes.  Strange structures grow in the keratin (horny) layer, allowing for possible drying and cracking of the skin, again causing water loss and the potential for secondary infection.  Fat and oil solvents help destroy the keratin layer, resulting in dry and cracked skin.  Another type of agent is the protein precipitants.  These are metal salts that precipitate and denature the protein in the skin, also weakening the integrity of the skin and allowing it to dry and crack.

Allergic Contact Dermatitis

In this case, contact between the agent, called sensitizer, and the skin initiates a cell mediated antigen-antibody immune reaction.  The body or the skin reacts to a concentration of a chemical or substance that normally do not produce a reaction on first contact.  However prolonged exposure causes the skin to become sensitized to that agent.  This sensitization goes through a three-period stage.  The first stage is what is referred to as the refractory period.  Here the exposure occurs, but there is no sensitization and usually there is no irritation so the individual does not realize that he or she is being exposed or that a reaction is occurring.  After the refraction period comes the induction period.  Here the sensitization process in the body occurs and usually takes somewhere between 10 and 21 days.  After the induction period comes the elicitation period.  Here the subject is re-exposed to the agent or the antigen, and this will result in a skin reaction after a delay of about 12-48 hours.  This reaction is an irritation reaction as a result of contact with the antigen.

Therefore the allergic contact dermatitis is a similar response to that of the irritant contact dermatitis, except that the exposure was to a lesser quantity of substance that normally causes contact dermatitis.  With the allergic contact dermatitis there is a very small amount of the agent which causes the reaction and the reaction is delayed, for as long as 12-48 hours after exposure.  Examples of agents that cause allergic contact dermatitis are metal salts such as nickel, chromium and cobalt, and organic chemicals such as isocyanates, acrylic products, and formaldehyde.  Recently, one agent that is attracting a lot of attention is latex which is from rubber and which can cause allergic contact dermatitis.  This has become a major concern in the health care field where latex gloves are used.

Chemical Burns

Skin contact with corrosive chemicals or hot substances cause severe ulceration of the skin.  The agents that cause chemical burns are mainly the acids and alkalis, with the alkalis creating a softer burn, but one that is much more painful.  Both compounds result in necrosis of the cells.  These chemicals actually burn or create ulcers in the skin, allowing secondary infection and water loss to occur.  It is extremely important to have rapid removal of these corrosive agents.  For severe cases emergency deluge shower is needed to flush the chemicals off the skin.  In mild concentration exposure, soap and water may be used.  However, it is imperative that you know the chemical involved because there are chemicals such as quicklime (calcium oxide) that produce an exothermic reaction when mixed with water.

Hydrogen fluoride

Two corrosive substances need to be mentioned in reference to their “odd ball” characteristics.  The first is hydrogen fluoride or hydrofluoric acid.  This is one of the strongest acids known.  It creates intense pain as necrosis develops.  It is a progressive agent in that there is often delayed deep tissue destructive reaction (necrosis).  It has a tremendous effect on the calcium which exists within the system, producing hypocalcemia .  This condition relates to the reduction of the blood calcium level and results in the twitching and spasm of muscle tissue.  One of the ways to treat hydrogen fluoride burns is with calcium gels or calcium injections into the body. This procedure helps to calm the hypocalcemia.

White phosphorous

The other “odd ball” corrosive is white phosphorous.  White phosphorous must be contained under a liquid medium, usually water, as it will burn in air and will stick to the skin.  If white phosphorous is found on skin, it must be cut out, usually under water, so it will not react.  White phosphorous requires special attention and is normally only dealt with in laboratory situations.

Chemicals are not the only causes of burns. Burns can also be caused by hot substances such as hot water, molten metal as well as energies such as flame and electrical energy.

Photodermatitis

There are chemicals that do not cause skin disorders directly.  However, the exposure to sunlight would activate or stimulate the chemicals to become irritating or even forming different toxic chemicals.  This disease process is also called photosensitization.  Examples of photosensitizers are coal tar (creosote, pitch), some dyes, and drugs.  If the worker is exposed to sunlight after the exposure to a photosensitizer, there is a resulting adverse reaction to sunlight.  These adverse reactions are called phototoxicity, where the reaction involves a non-immunological response similar to a radiation exposure.  The second response is described as photoallergy, where there is a reaction which is immunologically based and typical of the allergic contact dermatitis.  A third reaction is a depigmentation of the skin, which is a condition that results in white blotches of the skin.

Chemical Acne

There are two different types of acne.  The first is simple acne or acne vulgaris which humans experience throughout the adolescent age.  This type of acne is caused by oils, greases and creosotes that block pores, resulting in keratinization of the oil glands and ducts.  Little keratin cysts are produced in the sebaceous glands, which results in acne formation.

In terms of occupational exposure, chemical acne may originate from two sources: contact with hydrocarbon agents and exposure to halogenated hydrocarbons.  Examples of high molecular weight hydrocarbons that cause acne are cutting oils, coal tar oils.  Acne caused by exposure to halogenated hydrocarbons is also called chloracne; examples of such chemicals are polychlorinated biphenyls (PCBs).  Chloracne is a relatively rare illness; however it serves as an important evidence of exposure to chlorinated hydrocarbons.  Chloracne is also an important example in which the skin will display a disease but not where the contact occurred. The effects of chloracne causing agents in human have been well documented  through a series of industrial disasters such as the incidents of rice cooking oil contaminated with PCBs in Japan and Taiwan in 1979.

Introduction

Control measures used to prevent dermatosis follow the same general principles of hazard controls.  These can be categorized into the following five areas:

• engineering controls,
• personal protective equipment,
• personal hygiene,
• emergency response, and
• worker education.

Engineering Controls

Engineering controls should be considered first. They can be implemented by either enclosing the source of the hazard or isolating it.  If the source is a gas or vapour, usually local exhaust ventilation is used to remove the gas or vapour so that worker exposure can be avoided.  If it is a solid or a liquid, some type of shield can be used to protect against a splash or spill.  One way would be the use of automatic feed-lines and dispensers rather than manual handling.  Also, a non-irritating chemical or compound could be substituted for the irritating one.  Engineering controls remove the harmful hazardous agents from the worker.

Personal Protective Equipment

As a last resort, personal protective equipment (PPE) can be used to protect the worker.  In the case of protecting against skin disorders we can use gloves, boots, aprons or face shields to prevent skin contact with the chemical or physical agents.  It is very important when choosing personal protective equipment for skin protection that the users understand the nature of the chemical and the performance characteristics of the protective equipment.  The material used in the personal protective equipment is critical in providing an effective barrier between the chemicals and the skin.

Selection of the proper protective materials should be based on the specific chemical and physical properties of the chemicals and physical agents to which the worker is exposed.  For example, rubber gloves are adequate for protection against water-soluble agents, but would deteriorate when exposed to alkalis, whereas synthetic rubber such as neoprene is resistant to the alkalis, but is easily deteriorated by chlorinated hydrocarbons.  The safety equipment supplier’s material chemical resistance chart must be consulted before selecting the proper glove or other skin protective equipment.

Personal Hygiene

Another extremely important control measure with respect to the protection against skin disorders is personal hygiene.  Frequent hand washing is critical in reducing the contact time between harmful agents and the skin.  The workplace should have adequate washing and locker facilities and policy regarding good personal hygiene – washing of the skin, washing of the work clothes, and the use of a double locker system so that the work clothes will not contaminate the street clothes and carry the harmful agent home.

Some workplaces provide barrier creams and lotions as a form of skin protection.  These are considered to be the least effective, but depending on the activity, will provide some protection.  It is important to know what materials we are protecting against, whether it is a water, oil or solvent, and we must seek a barrier cream that will repel the agent of concern.

 

Emergency Response

Lastly, a first aid and emergency response system is imperative – eyewash, emergency deluge showers, and in some cases, special powders which nullify the effect of specific chemicals.  Specifications on eyewash and shower equipment are given by standards such as the ANSI (American National Standards Institute) Z358.1-2014 Standard on “Emergency Eyewash and Shower Equipment.”  Among other requirements, the emergency shower has to be located in accessible locations that require no more than 10 seconds to reach.  This ANSI Standards is reviewed again later in this module.

Education

With all these controls, it is necessary to educate and train workers and those involved in the workplace in the application of these methods and the use of personal protective equipment.  The best defence against occupational skin disease is to encourage early reporting of skin disorders to medical professionals.

Introduction

The skin may be the first organ that meets the chemical and physical agents, but the eye is the organ that is most vulnerable to occupational disease and injury.  The eye, a complex sensory organ, is at a much greater risk than the skin, lungs, ears or other target organs, and thus requires great protection in the practice of occupational health and safety.

The function of the eye is to translate or transform radiant light energy into neuro-electrical energy which is transmitted to the brain allowing the understanding of the messages from this light energy.  This translation is called vision.  Anything that interferes with this transmission of light energy into the neuro-input is a hazard.

Anatomy of the eye

Figure 6-3 shows the major parts of the eye.  The parts of the organ that serve the function of vision include the cornea where the light enters the eye and passes through the pupil, the iris which controls the entry of light, the lens which provides focus, and the retina which converts light energy into messages to the brain.  The eyeballs and lids are covered by a layer of skin, and this skin is subject to the same inflammatory responses as skin elsewhere on the body.

Hazards affecting the Eye

There are four different types of hazards that may affect the eye:

• chemical,
• mechanical,
• physical, and
• biological.

Chemical

Chemical eye hazards exist where the worker experiences acute exposure to irritants in either a solid, liquid, gas or vapour states.  These exposures can result in chemical burns, which lead to scarring of the cornea, and will interfere with the transmission of light energy onto the back of the eye or retina.  This results in a blurred vision because of the improper transmission of the light energy. Also, because of the high moisture levels in the eye, absorption of these irritants or chemicals in the eye is possible, especially if the hazardous compounds are water-soluble.  In such cases, absorption will occur readily and will lead to other systemic problems as these chemicals move throughout the body.

Mechanical

There are three forms of mechanical hazards and they are in forms of a blow, cut, laceration, or invasion of foreign objects.

Blows from Blunt Objects

This form of mechanical hazard relates to a blow from a blunt object.  The blunt object can be a piece of wood, metal, rock, or other substance.  It is like the fist in the face that a boxer may receive in a boxing match.  The blow results in contusion (bruising and swelling) and this causes an increase in the internal pressure within the eye, usually in the front compartment of the eye, the aqueous humour.  This will lead to a build up of pressure causing the disease known as glaucoma.  Glaucoma, if not treated, interferes and damages the optic nerve, resulting in a lack of vision.  It is very important to prevent physical blows to the eye and the resultant pressure build up.

Cut or Laceration

This second form of mechanical hazard is a cut or laceration from sharp objects.  The amount of damage done depends on how severe and where exactly the laceration or cut occurs.  If there is any cut to the cornea (the outside of the eye) the scar tissue can interfere with the transmission of the light energy on its way back to the retina and will interfere with vision.  A severe cut and laceration that damages the eyeball and retina and/or nerve, can be extremely harmful to the health of the eye.

Foreign Bodies

The third type of mechanical hazard is that of invasion by foreign bodies, such as nuisance dusts.  These dusts or foreign bodies interfere with the conjunctiva, resulting in conjunctivitis and irritation of that membrane.  Conjunctivitis causes interference with light transmission and irritation of the eyelashes and eyelids as they move over the eyeball.

Physical

Examples of physical hazards are thermal heat burns and radiation burns.  These burns result in damage to the eyelids and eyelashes, the conjunctiva, and also to the cornea.  Damage to the cornea results in scar formation and interference with transmission of the light energy and vision.  An example is the exposure to ultraviolet (UV) light from arc welding operations.  This condition is known as the “welder’s flash” which is an acute irritation of the cornea and conjunctiva.  Protection against UV radiation from the sun is also necessary through the wearing of sunglasses by outdoor workers.

Biological

Biological agents such as virus or bacteria can enter the eye.  These agents can cause irritations and infections of the conjunctiva resulting in Conjunctivitis, which is a superficial inflammation or infection involving the conjunctiva. Conjunctivitis is also commonly known as “pink eye”. Bacterial and viral pink eye is considered to be contagious.

The Eye’s Natural Protective Mechanisms

The eye possesses natural protective mechanisms against different types of eye hazards. These include the orbital cavity of the skull, the blinking reflex mechanism, the conjunctiva of the eye, and the secretion of the lacrimal glands.

Orbital cavity

The first form of natural protection is the orbital cavity.  It is a bony socket in which the eyeball sits and protects the posterior 4/5 of the eyeball itself, or the back section.  It could not protect the whole eyeball since this would prohibit light from entering the eyeball.

Blinking reflex

The second form of natural protection that the eye has is the blinking reflex, which is the action of the eyelids and eyelashes working together such that when any foreign object comes toward the eye they close in a blinking reflex.  The eyelids and eyelashes protect the front, or anterior portion of the eye.

Conjunctiva

Another form of natural protection that the eye has is the conjunctiva.  The conjunctiva is the smooth tissue that lines the inside of the eyelids and the outside of the eyeball itself.  This provides a smooth surface for articulation of the eyelids as they open and close, protecting the eye.

Lacrimal glands

The fourth form of natural protection that the eye has is the secretion from the lacrimal glands.  These glands are responsible for tear secretion.  These tears contain lysozyme, an antibacterial enzyme which helps in cleaning the conjunctiva and the eye.  As shown in Figure 6-4, the tears are released from the lacrimal glands and follow the pathway of the arrow down towards the medial part of the eye by the nose.  The tears then enter the lacrimal sac which leads down to the nasal cavity by the lacrimal duct.  The tears perform a cleansing action as they pass over the eyelid.

It is quite common that these defence mechanisms work together to protect the eyes.  For example, if you get an insect in your eye while riding your bike, you would first blink and then tears would be secreted from your lacrimal glands to wash out the foreign object.  The tears flowing over the conjunctiva carries out a cleansing process as the eyelids move back and forth over the eyeball itself.

Figure 6-5: Work of the Lacrimal Glands

Introduction

The control of eye hazards can be addressed under the following three areas:

• environmental controls,
• personal controls, and
• emergency response.

Environmental Controls

In any workplace, a survey should be conducted to outline all the potential eye hazards and to identify where they exist.  Job-hazard analysis should be carried out to determine the feasibility of controlling the exposure by engineering means.  An example of engineering control is process modification through automation – by automating the process and removing the workers from potential eye hazards.  Another example is to isolate the process or the hazard by the use of shields to protect against eye hazards such as flying chips or splashing liquids.

The provision of regular maintenance programs on process facilities, equipment and safe operating procedures would reduce the potential risk for eye hazard exposure due to equipment failure or accidents.  When looking at these environmental control measures, one can see that they require strong commitments from management and supervisory staff to make sure that the programs and practices are maintained.

Personal Controls

Once all the environmental controls are in place it is critical to develop the personal controls.  The first action among the personal controls is that of worker education and training.  This involves training on the skills and procedures required to do each job so that the worker can follow good work practices to avoid eye hazards.

The second personal control lies in the proper selection and use of personal protective equipment, in this case, eye protection.  The workers must be educated and fully trained in the reason why certain type of eye protection is selected.  Eye protective equipments are designed for specific protection such as chemical eye goggles for the protection of chemical splashes and the eye protection with proper shading for welders.  They must learn how to fit the protective equipment properly before it is used.  Standards on eye protection are published by agencies such as the Canadian Standard Association and should be consulted.

As well, workers should be trained in the use of the eyewash stations if there is a chemical splash or spill in the eye.  Training on how to use all other first aid techniques to reduce physical bruises and contusions should also be provided.

Finally, signs regarding the eye protection policy must be posted.  Management should have an enforcement policy so that workers understand that the use of personal protective equipment including eye protection is deemed necessary to perform certain job or in designated area.  Workers must be made aware of the necessity and importance of protecting the eye.

Emergency Response

There are two important aspects of emergency response regarding exposure to eye hazards.  They are emergency eyewash and first aid.

Eyewash

The provision of emergency eyewash station is a mandatory requirement in all workplace health and safety regulations whenever there is a potential worker exposure to a substance that may cause injury to the eyes.  The American National Standards Institute (ANSI) Standard  Z358.1-2014 titled: “Emergency Eyewash and Shower Equipment” specifies the designs and installation requirements of the emergency eyewash equipments.  Of the many specifications and requirements under the ANSI Standard, four are highlighted below:

• The eyewash must be accessible within a travelling time of not more than 10 seconds from the eye hazard location to the eyewash station.  This is extremely important because every second counts when dealing with a chemical exposure.  Most experts agree that the first-aid or eyewash response, if any, to be given within 15 seconds following exposure to a chemical determines whether there will be permanent damage to the eye.
• The eyewash must be capable of providing a flushing liquid (water) for a minimum of 15 minutes. In order to prevent any potential damage after an exposure, the eyes must be flushed or rinsed out for 15 minutes or longer continuously depending on the irritant or corrosive properties of the chemicals of concern. This also means that the eyewash bottle one commonly observed in workplaces is inadequate by itself if emergency eyewash is required.
• The eyewash should be designed to deliver flushing fluid at a tepid or lukewarm temperature. “Tepid” is defined as temperatures between 16 to 38^o C. In circumstances where chemical reaction is accelerated by flushing fluid temperature, medical advice must be obtained.
• Training regarding use of the eyewash is essential.  Eyewash stations look like a simple water fountain, but in an emergency situation workers can become very disoriented and confused.  Therefore they must be well informed about the location and the operation of the equipment so that they can respond quickly in emergency situations.  One trick when teaching workers how to reach the eye wash stations is to train by using a blindfold.  This trains the worker to move without having vision.  The careful planning and training about emergency eye wash stations will ensure effective use of these facilities when the need arises.

First-Aid 

There should be provision for first-aid stations properly equipped with the accessories for immediate treatment of eye injuries.  It is critical that the first-aid kits provided are specific for the eye hazards of concern.  Workers should be trained in emergency first aid procedures as mentioned earlier as part of personal control measures.

What’s next

In the next module we will look at toxic effects of various agents on important systems and organs of the body: liver, kidney, cardiovascular system, nervous system and reproductive system.

Review

Skin is a protective organ that covers the entire body.  Other than acting as a barrier between the internal body organs and external hazardous agents, the skin also provides a mechanism for body temperature regulation and sites for sensory receptors.  However, skin is also exposed to workplace hazards including chemical, biological and physical agents as well as mechanical energies resulting in various occupational skin diseases or injuries.  Controls of skin hazards in the work environment must include provisions for engineering controls as well as having emphasis on personal protective equipment, personal hygiene and emergency response facilities.

The eyes are highly sophisticated and complex organs that require a great deal of protection to maintain their proper function.  Therefore, an eye protection program is imperative in every workplace where eye hazards exist.  When planning this program, we must realize the various types of eye hazards.  There are hazards caused by exposure to harmful chemical and physical agents.  Protection against mechanical hazards such as blows to the head and contusions is a concern in some work environment. Also, exposure to physical agents such as radiation and heat can also cause damages to the eye. Similar to control measures for skin exposure hazards, the controls of eye hazards also focus on environmental and personal control methods and emergency response facilities such as eyewash equipment.