Work Study and Ergonomics

Introduction

Dust is as an aerosol composed of solid inanimate (non-living) particles, as defined by the ILO. The term aerosol implies that airborne particles are carried in or contained in air which may be inhaled. An aerosol can embrace liquid droplets as well as solid particles.

Some dusts are fibro-genic that causes fibrotic changes to lung tissue or toxic, they eventually poison the body systems. Examples of fibro-genic dust are silica, cement dust and certain metals, whereas toxic dust may include arsenic, mercury, beryllium, phosphorous and lead. Some toxic dust, such as arsenic, has an acute effect. Others, such as mercury, have a chronic effect. A number of dusts, although not harmful to health, can have a nuisance effect, for example, dust from combustion of solid fuels.

Definitions Relevant to Dust and Fumes

Particulate–It is a collection of solid particles, each of which is an aggregation of many molecules.

Mist–It is airborne liquid droplets, e.g., oil mist.

Fumes–These are airborne fine solid particulates formed from the gaseous state usually by vaporization or oxidation of metals, e.g., lead fume.

Vapour–These are airborne liquid droplets given off from the surface of a volatile liquid, e.g., trichloroethylene.

The Behavior of Dusts

All dusts are potential aerosols and the behavior of particles is influenced by

The unit of particle size is the micron, which equals one thousandth of a millimetre, designated µm.

When a particle falls in air it does not accelerate indefinitely. Eventually it reaches a speed at which air resistance equals its weight, and thereafter it falls at constant speed, which is called as ‘terminal velocity’. That depends to a great extent upon its size and density.

Physiology of the Human Lung

The lungs are enclosed in the thoracic cavity and have a sponge-like elastic texture. There are expanded or compressed by movements of the thorax in such a way that air is repeatedly taken in and expelled. They communicate with the atmosphere through the trachea or windpipe, which opens into the pharynx. In the lungs, gaseous exchange takes place.