Measuring airborne concentrations and air protection

Personal exposures are measured in the breathing zone of the worker.

Breathing zone: is described by a hemisphere of 300 mm radius extending in front of a worker's face and measured from the midpoint of an imaginary line joining the ears.

There are two general types of sampling techniques:

- active Sampling: using pump;

- passive Sampling: no pump.

There are three key elements of active sampling:

- a sampling pump - something to pull or push air;

- the sampling media - something to pull or push air through;

- a calibrator - something to indicate how much air has been pulled or pushed.

A variety of sampling media is used in sampling for gases and vapours:

- sorbent tubes;

- filters;

- impingers: are specially designed glass bottles that are filled with a collection liquid specified in the sampling method for specific chemicals;

- sampling bags;

- passive samplers: the collection of airborne gases and vapours at a rate controlled by a physical process such as diffusion through a static air layer or permeation through a membrane WITHOUT the active movement of air through an air sampling pump.

Requirements for sampling instruments are:

- to detect airborne contaminant at least at concentration a half of exposure standard in exhaust air;

- and the third of exposure standard in influx air;

- acceptable error is ±25% of measured value.

Airborne contaminants may force to have either antagonistic or synergistic effects.

In first case they are of multidirectional action, in the second – unidirectional. Those types should be considered for assessing concentrations against the standards.

Acceptable condition for multidirectional hazards C₁£TWA₁, C₂£TWA₂...

Acceptable condition for unidirectional ones

Atmospheric air can be referred to inexhaustible resources. However air protection takes an important place in ecology and offers variety of purification methods.

Purification from dust: dust catchers «dry» and scrubbers «wet».

Purification from gases: absorption methods, adsorption methods.

Absorption methods remove airborne contaminants by the liquid.

In absorber gas and liquid move contraflow what’s followed by chemical reaction.

Absorbers advantages: simple, reliable and have high degree of purification.

Disadvantages: cumbersome equipment, salvaging wastes.

Adsorption methods trap airborne chemicals on the surface of solid bodies (sorbents).

Adsorbers advantages: no chemical reaction, adsorbed gases and sorbent can be recycled.

Practice:

Assess the given concentrations of airborne contaminants: 10 mg/m³ of white spirit and 0.01 mg/m³ of lead, which make a group of unidirectional contaminants, and; 50 mg/m³ of gasoline.