Chemical Health

• 1. 2E1: Chemical Health Hazards Measurement and Analysis

2. Purpose of Sampling

• 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 measurementsto assess average exposure over a given time period

• • Continuous measurementsthat can detect short-term acute exposure to high concentrations of contaminants

• • Spot readingsto measure acute exposure if the exact point in time exposure is known

3. HSG173 - Monitoring Strategies for Toxic Substances

• 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

4. HSG173 - Monitoring Strategies for Toxic Substances

• 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.

5. HSG173 - Monitoring Strategies for Toxic Substances

• 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

6. HSG173 - Monitoring Strategies for Toxic Substances

• Initial Appraisal:

• • Simple qualitative tests can be carried out:

• • • Dust lamps

• • • Smoke tubes

• • • Stain tubes

7. HSG173 - Monitoring Strategies for Toxic Substances

• Strategies:

• • First level for basic surveys

• • Second level for more detailed surveys

• • Third Level for surveys needing high degree of sophistication

8. HSG173 - Monitoring Strategies for Toxic Substances

• 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

9. HSG173 - Monitoring Strategies for Toxic Substances

• Second level strategies:

• • Appropriate for most detailed surveys and for routine monitoring

• • Emphasis on accurate measurement of average exposures and relating them to OELs

• • Entire periodof exposure should be covered

10. HSG173 - Monitoring Strategies for Toxic Substances

• 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

11. HSG173 - Monitoring Strategies for Toxic Substances

• 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?

12. MDHS

• Series of detailed descriptions of analytical methods approved by HSE

• Provide reliable and consistent methods

• Covers samplingANDanalysis

13. Solid Particulate Sampling

• 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

14. Solid Particulate Sampling

• 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

15. Solid Particulate Sampling

• 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

16. Solid Particulate Sampling

• 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)

17. MDHS for Gravimetric Determination of Dusts

• 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/m 3 )

18. MDHS - Sampling Asbestos Fibres in Air

• 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)

19. Sampling for Gases & Vapours

• 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

20. Grab Sampling

• Evacuated flasks

• • Atmosphere drawn in

• Gas/Liquid displacement container

• • Flask connected to a pump

• Flexible plastic containers

• • Plastic bags

• Hypodermic syringes

21. Continuous Sampling - Active

• Liquid sorbents

• Cold traps

• Plastic sampling bags

• Solid sorbents

• • Charcoal or Silica gel

22. Continuous Sampling - Active

• Sampling equipment:

• • Pump

• • • Adjustable flow rate

• • • Able to be worn if personal sampling required

• • Flow measurement

• • • Important to know flow rate to calculate exposure

23. Continuous Sampling - Passive

• Diffusive samplers

• • Badge or tube type

• • Factors affecting performance:

• • • Temperature and pressure

• • • Humidity

• • • Concentration variations

• • • Sorbent efficiency

• • • Face velocity

24. Sampling Procedures for Gases and Vapours

• Sample positioning:

• • General working atmosphere (grab sample)

• • Operators 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

25. Analytical Techniques

• 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

26. Gas Chromatography

• 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

27. Atomic Absorption Spectroscopy

• 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

28. Infra Red Spectroscopy

• 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

29. X-Ray Diffraction

• 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

30. Optical Microscopy

• 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