Unit-iv unit-iv environmental Hygiene

Methods of air sampling

3. Impingement

3. Impingement

• To collect atmospheric particles in a liquid medium
• The air is sucked through a glass instrument at a defined rate into the fluid
• The microbial load: determined by examining the fluid

4. Precipitation

• The precipitation of atmospheric particles in two ways:

1. Thermal precipitation

• A slowly moving air current (3 lit/min) is directed between heated & cooled surfaces (distance 0.038 cm)
• The heated wire/surface repulses the particles towards cold surface
• They get collected in cold surface
• The organisms are then transferred on to the agar medium

2. Electrostatic precipitation

• Collects the organisms on the basis of their electric charge
• It is a highly efficient instrument for collecting the airborne particles

Methods of air sampling

5. Filtration

5. Filtration

• The microorganisms are trapped on a filter (cotton, glass wool or paper) or membrane filter
• Membrane filter technique is considered to be better for the purpose
• Air is filtered through the membrane
• The particles (with microbes) are impunged on this membrane
• The membrane is then placed on a paper saturated with an appropriate medium & incubated

6. Sieve (cascade) samplers

• It is desired to collect samples of air on the basis of the particle size of the pollutant
• Sieves of varying sizes are arranged in a cascading manner (one upon the other)
• Larger particles are collected on top
• Smaller ones towards the bottom sieves
• Cascade impactor is a highly efficient trap

Methods of air sampling

Control of air pollution

• Minimize the production & release of pollutants near the animal or human dwellings
• Control of dust particles: by improving sanitary conditions within the houses
• Frequent washings of floor & equipment: controlling the dust within the buildings
• Vacuum cleaners: used effectively
• Proper ventilation: a prompt clearance of foul gases & particulate pollutants

Filters can be installed to check the entry of external contaminants

• Use of laminar air flow systems for closed compartments/ cabins

Allows unidirectional passage of air through cellulose acetate filters