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Air sampling

Air sampling:-
Basic need of air quality sampling and work environment monitoring and analysis is to find the level of pollution and to work out strategy to reduce it. Need of sampling and monitoring is statutorily suggested by Form no. 37,Rule 12B of the Gujarat Factories Rules. The format calls for identification of airborne contaminants, sampling instruments and methods, number of samples and comparison of measured value with the TWA concentration in 2nd schedule of the Factories Act to assess the working environment also the number of workers exposed to that. Correct record of such workplace monitoring is essential for good health and good housekeeping. 
Need of sampling and monitoring is also inferred from the types, sources and hazards of air pollutants. Monitoring is more than air sampling or medical examination of a worker. It includes a series of actions to assess the protection necessary. 

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Purpose and types of Air sampling:-

Purpose of sampling are (1) To determined type and concentration of exposure due to health hazards to workers (2) To determine the types and effectiveness of the control measures provided, any change if necessary in them and new control measures to be provided (3) To investigate complaints and (4) For research purposes. 
Types of Air sampling:

1) Personal Sampling. 
2) Area Sampling. 
3) Grab Sampling. 
4) Integrated Sampling. 

In personal sampling the sampling device is worn by the worker near his breathing zone to evaluate personal or individual exposure to him. 

In area sampling the air samples are taken at fixed places at Workroom or confined spaces to evaluate general concentrations of flammable, explosive or toxic material in the air for the purpose of isolation or restriction to work for leak detection, ventilation failure, equipment malfunction etc. 

Grab sampling:- Short period (instantaneous) sampling at a particular time ( at least two samples within 5 minutes) e.g. peak value of NH3 or CL2 at a particular time. The sample is collected in evacuated flask or plastic bag, sealed and sent to a laboratory where trace analysis is carried out by gas chromatography, IR spectrometry etc. Direct reading instruments can also be used for grab sampling. Temperature and pressure should be recorded during sampling. It should not be used for recative gases. 

Integrated sampling- Long period sampling is called integrated sampling. Integrated air sampling is carried out by direct reading instruments (e.g. gas detector tubes or digital meters) to measure STEL value for 15 minutes and TLV for 8 Hrs TWA limits. An air-sampling train consisting of air-inlet orifice, collection media ( solid or liquid sorbent, filters and passive monitors), air-flow meter, flow-rate control valve and suction pump, is used by qualified and trained personnel. 

Direct reading gas and vapour monitor include:-
1) Colorimetric device- stain tubes and hand or battery operated pump. 
2) Colorimetric paper tape samplers. 
3) Electrical Instruments. 
4) 0 monitors. 
5) CO monitors and 
6) IR analysers. 
Types of sampling is also classified as 
1) Passive or diffusive air sampling which involves collection of airborne gases/vapours through a diffusion barrier onto absorbing medium without the use of air sampling pump. 
2) Active air sampling which involves collection of airborne contaminants by means of a forced movement of air by a sampling pump and through appropriate collection medium i.e. filter. 
. Selection of equipment for air-sampling is important and depends on many factors such as purpose of sampling, type of sampling, type of equipment available, nature of toxicant, environmental conditions, required accuracy and sensitivity, reliability, property of air-contaminant, presence of other chemicals which may mix or interfere, duration of sampling, cost etc.
Air sampling methods. 

Two basic methods employed to collect the Gaseous contaminants are:

1.Use of a gas collector, such as an evacuated flask. The collector is resealed immediately to prevent loss before to the sample is analysed and 
2.Passing a known volume gas or air through an absorbing medium to remove the desired contaminants from the sampled atmosphere. The absorbing medium is chosen according to it's efficiency for a particular contaminants. 

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