Measurement and Analysis

To identify and quantify chemical health hazards

Health effects can be acute or chronic, so there are different types of measurement to account for this: Long-term measurements to assess average

exposure over a given time period

Continuous measurements that can detect short-term acute exposure to high concentrations of contaminants

Spot readings to measure acute exposure if the exact point in time exposure is known

2 types of sampling:

Static sampling

Primary aim is to assess effectiveness of engineering controls or measure plant emissions into work environment

Levels should be set well below personal exposure limits

Personal sampling

Assess individual exposure

Factors influencing airborne concentrations:

No. of sources of contaminant

Rates of release from each source

Type and position of each source

Dispersion or mixing of contaminants

Ambient conditions e.g. wind speed, air temp.

Before devising sampling strategy, carry out initial appraisal. Info. required: Substances which occur in workplace

Airborne nature of substances

Hazardous properties of substances

Synergistic effects

Possible exposure by inhalation, ingestion, skin contact?

During which processes/tasks will exposure occur?

Groups/individuals at risk

Likely pattern and duration of exposure

Initial Appraisal:

Simple qualitative tests can be carried out:

Dust lamps

Smoke tubes

Stain tubes

Strategies:

First level for basic surveys

Second level for more detailed surveys

Third Level for surveys needing high degree of sophistication

First level strategies:

Used where crude quantitative information is required so that decisions can be taken as to whether problem actually exists, prior to conducting detailed survey

Divide population into groups in relation to work or degree of exposure

High risk groups can be studied in detail

Personal sampling, especially at peak periods

Second level strategies:

Appropriate for most detailed surveys and for routine monitoring

Emphasis on accurate measurement of average exposures and relating them to OEL’s

Entire period of exposure should be covered

Third level strategies:

Occasionally high degree of sophistication required

E.g. if all reasonably practicable steps have been taken and exposure is still close to OEL; or

Where OEL is very low so small changes in exposure are significant

Consideration of results should always lead to answers to 5 questions:

Is immediate action necessary to eliminate or reduce exposure?

Is immediate action necessary to re-establish adequate control?

Is a programme of planned improvements necessary?

Is a more detailed survey required?

Should routine monitoring be implemented or continued?

Series of detailed descriptions of analytical methods approved by HSE

Provide reliable and consistent methods

Covers sampling AND analysis

2 Fractions:

Inhalable fraction:

Total particles inhaled through nose and mouth

Respirable fraction

Less than 10 microns

Able to penetrate the respiratory system as far as the alveolar region

Fibrous particles:

Shape is as important as size

Long thin fibres more dangerous

Components: Sampling head

Size selection Cyclones to separate respirable fraction

Filters Used to collect sample before assessment

Wide range depending on contaminant

Pumps Must be able to be worn on body if personal sampling

required

Flow meter required

Static sampling:

Complete assembly includes filter, pump and flow meter

Left unattended in workplace

Use cyclones to remove larger particles

Personal sampling:

Preferred technique - more realistic measurement of exposure

Cyclones used to remove larger particles

Direct Reading Instruments:

Gives instantaneous result

Can be:

Light scattering

Beta particle attenuation

Oscillating micro-balance (quartz crystal oscillation changes with build up of dust)

Measured volume of air drawn through filter

Mass of dust collected is determined by weighing filter before and after sampling

Size selection devices can be used to measure respirable dust

Volume of air passing through filter is calculated by multiplying flow rate (cubic m per minute) by sampling time (minutes)

Weight gain of filter (mg), divided by the volume sampled, gives average dust concentration in mg per cubic meter of air (mg/m3)

Similar to dust, except: Open faced filter holder

Membrane filters which can be rendered transparent to allow fibre counting by phase contrast microscopy

Flow rate is specified and measurement must be over 4 hour period

Fibres are counted on membrane filter

Concentration is calculated by dividing total no. of fibres collected on filter by total volume of air to give fibres per millilitre (f/ml)

Grab Sampling: Sample taken in flask, bottle bag etc.

Useful for peak concentration or when concentrations are constant

Continuous or Long-Term Sampling: Sample removed from air over measured time

period and concentrated by passage through solid or liquid sorbent

Useful if: Concentration varies time with time

Concentration is low

TWA exposure is required

Evacuated flasks

Atmosphere drawn in

Gas/Liquid displacement container

Flask connected to a pump

Flexible plastic containers

Plastic bags

Hypodermic syringes

Liquid sorbents

Cold traps

Plastic sampling bags

Solid sorbents

Charcoal or Silica gel

Sampling equipment:

Pump

Adjustable flow rate

Able to be worn if personal sampling required

Flow measurement

Important to know flow rate to calculate exposure

Diffusive samplers

Badge or tube type

Factors affecting performance:

Temperature and pressure

Humidity

Concentration variations

Sorbent efficiency

Face velocity

Sample positioning:

General working atmosphere (grab sample)

Operator’s breathing zone (TWA sample)

Close to contaminant generation (continuous monitored sample)

Sampling frequency:

Statutory in some cases (asbestos every 4 hours)

Depends on level of risk

Most involved subjecting substance to burst of energy and examining way substance responds

Response is characteristic of substance and can be used as “fingerprint”

Magnitude of response can be used to estimate how much of agent is present

Techniques: Gas Chromatography

Atomic Absorption Spectroscopy

Infra Red Spectroscopy

X-Ray Diffraction

Optical Microscopy

Chemical is carried down an absorbent column by a carrier gas

The length of time the sample takes to travel down the column is unique to the substance

Size of spectrum peak indicates quantity of substance

Mixed substance can be separated

Used for metallic substances

If certain metals are heated to high temperatures in a flame, electronic changes in the metal atom cause a change in colour to the flame

Sample is injected into an air-acetylene flame and resultant spectrum is analysed by an atomic absorption spectrometer

Both identity and quantity of substance can be determined

Based on principle that chemical bonds that connect atoms into molecules are continuously vibrating and the energy of this vibration falls within the infra-red wavelength range

Infra-red radiation is passed through the sample and the absorption spectrum gives a characteristic fingerprint of the substance

Identifies and quantifies substance

Used for solid analysis

X-rays passed through a sample are diffracted in a characteristic fashion, which depends on the crystal structure and spacing between atoms

Gives characteristic fingerprint of substance

Mostly widely used for fibrous dust

Dust is collected on membrane filter, then counted under optical microscope

As sampling time and flow rate are know, fibres per unit volume can be calculated

Where it is necessary to determine type of asbestos, polarised light microscopy is used

Different types of fibre show different colours under polarised light