Chemical Health
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Transcript of 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:
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- Long-term measurementsto assess average exposure over a given time period
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- Continuous measurementsthat can detect short-term acute exposure to high concentrations of contaminants
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- 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:
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- Static sampling
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- Primary aim is to assess effectiveness of engineering controls or measure plant emissions into work environment
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- Levels should be set well below personal exposure limits
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- Personal sampling
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- Assess individual exposure
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4. HSG173 - Monitoring Strategies for Toxic Substances
- Factors influencing airborne concentrations:
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- No. of sources of contaminant
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- Rates of release from each source
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- Type and position of each source
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- Dispersion or mixing of contaminants
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- 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:
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- Substances which occur in workplace
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- Airborne nature of substances
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- Hazardous properties of substances
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- Synergistic effects
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- Possible exposure by inhalation, ingestion, skin contact?
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- During which processes/tasks will exposure occur?
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- Groups/individuals at risk
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- Likely pattern and duration of exposure
6. HSG173 - Monitoring Strategies for Toxic Substances
- Initial Appraisal:
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- Simple qualitative tests can be carried out:
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- Dust lamps
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- Smoke tubes
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- Stain tubes
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7. HSG173 - Monitoring Strategies for Toxic Substances
- Strategies:
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- First level for basic surveys
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- Second level for more detailed surveys
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- Third Level for surveys needing high degree of sophistication
8. HSG173 - Monitoring Strategies for Toxic Substances
- First level strategies:
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- Used where crude quantitative information is required so that decisions can be taken as to whether problem actually exists, prior to conducting detailed survey
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- Divide population into groups in relation to work or degree of exposure
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- High risk groups can be studied in detail
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- Personal sampling, especially at peak periods
9. HSG173 - Monitoring Strategies for Toxic Substances
- Second level strategies:
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- Appropriate for most detailed surveys and for routine monitoring
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- Emphasis on accurate measurement of average exposures and relating them to OELs
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- Entire periodof exposure should be covered
10. HSG173 - Monitoring Strategies for Toxic Substances
- Third level strategies:
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- Occasionally high degree of sophistication required
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- E.g. if all reasonably practicable steps have been taken and exposure is still close to OEL; or
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- 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:
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- Is immediate action necessary to eliminate or reduce exposure?
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- Is immediate action necessary to re-establish adequate control?
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- Is a programme of planned improvements necessary?
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- Is a more detailed survey required?
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- 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:
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- Inhalable fraction:
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- Total particles inhaled through nose and mouth
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- Respirable fraction
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- Less than 10 microns
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- Able to penetrate the respiratory system as far as the alveolar region
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- Fibrous particles:
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- Shape is as important as size
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- Long thin fibres more dangerous
14. Solid Particulate Sampling
- Components:
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- Sampling head
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- Size selection
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- Cyclones to separate respirable fraction
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- Filters
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- Used to collect sample before assessment
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- Wide range depending on contaminant
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- Pumps
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- Must be able to be worn on body if personal sampling required
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- Flow meter required
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15. Solid Particulate Sampling
- Static sampling:
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- Complete assembly includes filter, pump and flow meter
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- Left unattended in workplace
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- Use cyclones to remove larger particles
- Personal sampling:
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- Preferred technique - more realistic measurement of exposure
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- Cyclones used to remove larger particles
16. Solid Particulate Sampling
- Direct Reading Instruments:
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- Gives instantaneous result
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- Can be:
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- Light scattering
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- Beta particle attenuation
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- Oscillating micro-balance (quartz crystal oscillation changes with build up of dust)
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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:
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- Open faced filter holder
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- Membrane filters which can be rendered transparent to allow fibre counting by phase contrast microscopy
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- Flow rate is specified and measurement must be over 4 hour period
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- Fibres are counted on membrane filter
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- 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:
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- Sample taken in flask, bottle bag etc.
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- Useful for peak concentration or when concentrations are constant
- Continuous or Long-Term Sampling:
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- Sample removed from air over measured time period and concentrated by passage through solid or liquid sorbent
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- Useful if:
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- Concentration varies time with time
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- Concentration is low
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- TWA exposure is required
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20. Grab Sampling
- Evacuated flasks
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- Atmosphere drawn in
- Gas/Liquid displacement container
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- Flask connected to a pump
- Flexible plastic containers
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- Plastic bags
- Hypodermic syringes
21. Continuous Sampling - Active
- Liquid sorbents
- Cold traps
- Plastic sampling bags
- Solid sorbents
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- Charcoal or Silica gel
22. Continuous Sampling - Active
- Sampling equipment:
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- Pump
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- Adjustable flow rate
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- Able to be worn if personal sampling required
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- Flow measurement
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- Important to know flow rate to calculate exposure
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23. Continuous Sampling - Passive
- Diffusive samplers
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- Badge or tube type
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- Factors affecting performance:
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- Temperature and pressure
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- Humidity
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- Concentration variations
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- Sorbent efficiency
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- Face velocity
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24. Sampling Procedures for Gases and Vapours
- Sample positioning:
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- General working atmosphere (grab sample)
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- Operators breathing zone (TWA sample)
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- Close to contaminant generation (continuous monitored sample)
- Sampling frequency:
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- Statutory in some cases (asbestos every 4 hours)
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- 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:
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- Gas Chromatography
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- Atomic Absorption Spectroscopy
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- Infra Red Spectroscopy
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- X-Ray Diffraction
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- 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