RESPIRATORY FIBROGEN BASIC INFORMATION AND TUTORIALS

BASIC INFORMATION ON RESPIRATORY FIBROGEN

What are Respiratory fibrogens?

The hazard of particulate matter is influenced by the toxicity and size and morphology of the particle. Figure below gives typical particle size ranges for particles from various sources.

The critical size of dust (and aerosol) particles is 0.5 to 7 μm, since these can become deposited in the respiratory bronchioles and alveoli.

If dust particles of specific chemicals, e.g. silica or the various grades of asbestos, are not cleared from the lungs then, over a period, scar tissue (collagen) may build up; this reduces the elasticity of the lungs and impairs breathing.

The characteristic disease is classified as pneumoconiosis. Common examples are silicosis, asbestosis, coal pneumoconiosis and talc pneumoconiosis.

An appreciation of the composition and morphology of the dust is important in the assessment of hazard.

Thus, among silica-containing compounds, crystalline silicates and amorphous silicas (silicon dioxide) are generally not considered fibrogenic, whereas free crystalline silica and certain fibrous silicates such as asbestos and talcs can cause disabling lung diseases.

RATES OF CHEMICAL REACTION BASIC INFORMATION AND TUTORIALS

BASIC INFORMATION ON RATES OF CHEMICAL REACTION

What is the rate of chemical reaction?

Rates of chemical reaction
Whereas thermodynamics describes the energy requirements of a reaction, the speed at which it progresses is termed kinetics. It is important to be able to control the rate of chemical reactions for commercial and safety reasons.

If a reaction takes too long to progress the rate at which a product is manufactured would not be viable. Alternatively, if reactions progress too fast and ‘runaway’ out of control there could be dangers such as explosions.

The rate at which reactions take place can be affected by the concentration of reactants, pressure, temperature, wavelength and intensity of light, size of particles of solid reactants, or the presence of catalysts (i.e. substances which alter the speed of reactions without being consumed during the reaction) or impurities.

Catalysts tend to be specific to a particular reaction or family of reactions. Thus nickel is used to facilitate hydrogenation reactions (e.g. add hydrogen to C==C double bonds) whereas platinum is used to catalyse certain oxidation reactions. Sometimes care is needed with the purity of reactants since impurities can act as unwanted catalysts; alternatively, catalysts can be inactivated by ‘poisoning’.

The effect of temperature on different types of reaction is shown in figure below:

For reactions which progress slowly at room temperature it may be necessary to heat the mixture or add a catalyst for the reaction to occur at an economically-viable rate. For very fast reactions the mixture may need to be cooled or solvent added to dilute the reactants and hence reduce the speed of reaction to manageable proportions.

In general the speed of reaction

• doubles for every 10°C rise in temperature;
• is proportional to the concentration of reactants in solution;
• increases with decreased particle size for reactions involving a solid;
• increases with pressure for gas phase reactions.