Forms of Chemical Agent:

When we consider chemicals in the workplace we are not solely concerned with substance and preparations which are used directly in work such as paints or cleaning materials. We are also concerned with chemicals which arise from the work, such as the dusts or fumes given off during a process, for example when grinding or heating solid metals.

A chemical may be in the form of a substance or a preparation :

• A substance is a chemical element or a compound, including any impurities.
• A preparation is a mixture of substances, usually with a deliberately proportioned composition.

Liquids:

Many chemicals are supplied and used in the workplace in liquid form. They can vary from relatively harmless cleaning fluids through to highly toxic and corrosive acids and alkalis.

Gases:

A gas is a formless chemical which occupies the area in which it is enclosed. Its volume and state can be changed by the combined effect of increased pressure and decreased temperature. There are many toxic gases used in industry, such as chlorine, hydrogen sulphide, etc.

Vapours:

Vapour is the gaseous form of a liquid below its boiling point. There is an equilibrium or balance between the two phases or states. Heating a liquid causes evaporation. Solids also exist in equilibrium with vapour, hence we can smell them, but in most cases the amount of vapour is negligible.

Mists:

Mists consist of finely suspended droplets formed by condensation from a gas or the atomising of a liquid or from aerosols. Mists are created by many industrial processes, such as chromium plating or charging lead acid batteries and car paint spraying.

Fumes:

Fumes are fine particulate solids, which are created by condensation from a vapour, often after a metal has been converted to the molten state. The metallicfumes are usually the oxide of the metal and produce highly toxic fumes.

Dusts:

Dusts consist of solid particles of varying size and are created by such operations as grinding or sieving of solid materials, controlled detonations and various drying processes. In still atmospheres, dusts tend to settle under gravity and accumulate on surfaces. Where there is turbulence or air movement at least some element of the dust will remain airborne.

Aerosol:

Fine suspension of solid particles or droplets in a carrier gas.

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Health Risks from Blood Borne Viruses

Blood Borne Viruses are Hepatitis (causative agent for jaundice nd liver damage) and HIV – Human Immunodeficiency Virus ( Causative agent for AIDS – Acquired Immune Deficiency Syndrome). Contaminated body fluids can cause infection by contact with damaged skin, needle-stick injury and even splashing to the eyes and mouth.

Circumstances that a worker may be exposed to Blood Borne Viruses

Health care workers are more vulnerable to infection while handling body fluids of infected patients and when disposing infected needles. Waste disposal workers are other category of people who may contract infection while incorrect handling of clinical waste. 

Workers who are engaged in the transportation of body fluids are also vulnerable, who may inadvertently contract infection. Other circumstances that would lead to exposure to BBVs may be through injuries to infected person when occur at workplace such as cuts, bruise crush etc., and workers engaged in acts of tattooing and body piercing.

Control Measures to overcome the Health Risks from Blood Borne Viruses

The control measures to overcome the health risks from blood borne viruses would be correct Disposal of potentially contaminated material such as clinical waste; 

Prevention of needle-stick injuries by correct disposal of sharps in a sharps bin; 

Use of PPE such as gloves and eye protection when handling potentially contaminated material; Drawing up and enforcement of decontamination and disinfection procedure; 

Vaccination where appropriate (for hepatitis) for vulnerable persons;

Covering up the wounds; 

Procedures to deal with accidental exposure.

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Biological Hazard - Biological Agents

Biological agents are micro – organisms such as:

Fungi

Moulds, yeast and mushrooms mostly harmless to human but some can cause disease such as athlete’s foot and farmer’s lung, both fungal infections.

Bacteria

Single celled organisms that are found in vast numbers in and on the human body. Some are beneficial while others can cause disease such as legionnaires, leptospirosis etc.,

Viruses

Very small infections organisms that reproduction on living cells of human body. Example – Hepatitis

Possible routes of Entry for a Biological Agent

The possible routes of entry for a biological agent into the body would be 

inhalation – airborne micro-organisms, 

absorption through the skin, injection for example through cut and grazes, exchange of body fluids, and 

ingestion – contaminated food.

Control Measures to Reduce Risk of Exposure to Biological Agent

• In order to reduce the risk of infection from biological organisms we can adopt a number of control Measures such as cleaning and disinfecting
• The use of personal protective equipment like respiratory protection, aprons and gloves
• Engineering controls such as containment for example in glove boxes, can also be provided with local exhaust ventilation and the use of microbiological safety cabinets
• The introduction of procedures for the disposal of waste
• The prohibition of eating or drinking in the work area
• Vermin control
• Procedures for site monitoring and health surveillance
• Immunization and a good standard of personal hygiene.

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Local Exhaust Ventilation (LEV)

Local Exhaust Ventilation (LEV) is the standard control measure for dealing with dusts, vapours and fumes which are generated from a point source. The harmful contaminant is extracted at the point of generation using engineered systems to ensure that the direction of the ventilation flow is away the breathing zone of any operators.

LEV is a mechanical system of ventilation designed to remove a specific contaminant from its source, e.g. Welding fume. It consists of the following: a receptor or capture hood; ducting to remove the contaminant; an a irc leaning device, e.g. Filter to remove the contaminant from the air; a fan to ensure an adequate ventilation rate for the contaminant. This will be dependent on the size of the particles and the size of the LEV system; and a discharge point.

Examples of LEVs include:

• Glove boxes
• Fume Cupboards
• Captor Hoods
• Receptor Hoods

Factors that may reduce the effectiveness of a Local Exhaust Ventilation System (LEV)

The factors that may reduce the effectiveness of a local exhaust ventilation (LEV) are failure to position the hood close enough to the source of emission; damaged ducting; blocked, damaged, unsuitable or incorrectly installed filters; fan inefficiency perhaps due to wear or corrosion of the impeller blades; inappropriate initial design that was made further worse due to process changes; unauthorized alternations such as increasing the number of inlets; a build up of contaminant in the dusting and a blocked/ obstructed outlet; incorrect settings such as angle of dampers; scrubber saturation, and a failure to introduce procedures for the regular maintenance, inspection and testing of the system.

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Wood Dust Risk & Control Measures

Health Risk which could be associated with the wood dust

Wood dust is a ‘substance hazardous to health’ because it can cause serious non-reversible health problems, such as skin disorders; obstruction in the nose, and rhinitis; occupational asthma (mainly when cedar wood is used) and a rare type of nasal cancer.

Operations that produce high levels of Wood Dust Exposure

• Machining operations, particularly sawing, routing and turning; 
• Sanding, by machine and by hand; 
• Hand assembly of machined or sanded components; 
• The bagging of dust from dust extraction systems; 
• Using compressed airlines to blow dust off furniture and other articles probably for housekeeping or for preparing the furniture for coating varnishes and paints;

Control Measures that reduce the Risk from the Wood Dust

Set Exposure Limits
These are limits placed on the amount of dust in the air, averaged over an eight-hour working day. Workplace Exposure Limit (WEL) of 5mg/m3 is set by HSE(UK), which must not be exceeded. However, exposure must reduced to as low as ‘reasonably practicable’.

Dust Extraction
Provide dust extraction (also known as local exhaust ventilation or LEV) at woodworking machines to capture and remove dust before it can spread. Extraction system must to take into account the number and type of machines to be connected to it, and the layout of the workshop or factory. Fitting air flow indicators will help to know and maintain required air flow and extraction vacuum.

Education and awareness
Workers need to be educated about the risks from wood dust and the control measures required. They must be aware of the extraction system’s functioning and ways to improve efficiency of LEV system; never to sweep up or use compressed air lines as this will disturb the dust and allow it to become inhaled; clean up using a suitable industrial vacuum cleaner.

Respiratory Protective Equipment (REP)
Mask with appropriate cartridge for activities such as sanding may be needed and correct fitment is to be ensured.

Health Surveillance
As workers are at risk of acquiring asthma – a chronic case, health surveillance would be required to identify early symptoms. A low level health surveillance involving workers to complete questionnaire will be sufficient. Where high risk is involved (using red cedar wood), a higher level of health surveillance, including lung function testing, is needed.

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Routes of Entry of Toxic Substance into the Body

There are four main routes of entry for the toxic chemical into the body:

INHALATION - the substance is breathed in through the nose and mouth and down into the lungs. This is a significant route of entry for many toxic substances in the form of gas, vapour, mist, fume or dust.

INGESTION - the substance is taken in through the mouth and swallowed down into the stomach and then moves on through the digestive system. Unless there is a mistaken ingestion or cross contamination, this is a less significant route of entry since people are unlikely to swallow deliberately.

ABSORPTION through the skin - the substance passes through the skin and into the tissues beneath and then into the blood stream. Only some substance such as organic solvents can permeate.

INJECTION through the skin - the substance passes through the skin barrier either by physical injection such as needle-stick injury or through damaged skin such as cuts and grazes.

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Workplace Exposure Limits (WEL)

An Workplace Exposure Limit is an upperlimit on the acceptable concentration of a hazardous substance in workplace air for a particular material or class of materials. It is typically set by competent national authorities and enforced by legislation to protect Workplace safety and health.

Types of Exposure Limit:

Short term exposure limit (STEL)- maximum concentration of airborne contaminates too which employees may be exposed for a short period of time equal to 15 minutes.

Long term exposure limit (LTEL)- maximum concentration of airborne contaminants to which employees may be exposed over their entire working life for a reference period equal to 8 hours per day, 40 hours per week.

Purpose of WELs

The purpose of WEL is to combat the ill-health effects of being exposed to very high levels of the substance for quite short periods of time (sudden acute effects), and also to combat the ill-health effects of being exposed to relatively low concentration of substance for prolonged period or all hours of working day through an entire working life time (delayed chronic effects).

The aim is to ensure that the exposure to contaminants is below WEL, by having arrangements for monitoring the concentration of airborne substance in workplace along with suitable controls such as extraction system.

Limitations of WELs

Workplace exposure limits are set based on inhalation, whereas other routes are not considered. They are set with reference to male physiology of certain European countries and USA, hence it will have significant impact on race and gender. 

They becomes invalid if the environmental parameters, such that humidity temperature etc. in which the tests are carried out, vary largely with actual workplace environment. They don’t account for synergistic effect of multiple substances. 

Some limits are only ‘guidelines’. Some limits do not consider all the possible health effects of a substance such as dermatitis would not be considered with an airborne limit. 

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