B Part 11 Chemicals

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Chemicals

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B Part 11 Chemicals

  1. 1. Measurement and Analysis
  2. 2. 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
  3. 3. 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. 4. 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. 5. 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. 6. Initial Appraisal:  Simple qualitative tests can be carried out:   Dust lamps  Smoke tubes  Stain tubes
  7. 7. Strategies:  First level for basic surveys   Second level for more detailed surveys  Third Level for surveys needing high degree of sophistication
  8. 8. 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. 9. 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
  10. 10. 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. 11. 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. 12. Series of detailed descriptions of analytical  methods approved by HSE Provide reliable and consistent methods  Covers sampling AND analysis 
  13. 13. 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. 14. 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. 15. 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. 16. 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. 17. 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)
  18. 18. 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. 19. 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. 20. Evacuated flasks  Atmosphere drawn in  Gas/Liquid displacement container  Flask connected to a pump  Flexible plastic containers  Plastic bags  Hypodermic syringes 
  21. 21. Liquid sorbents  Cold traps  Plastic sampling bags  Solid sorbents  Charcoal or Silica gel 
  22. 22. 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. 23. Diffusive samplers  Badge or tube type  Factors affecting performance:   Temperature and pressure  Humidity  Concentration variations  Sorbent efficiency  Face velocity
  24. 24. 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 
  25. 25. 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. 26. 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. 27. 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. 28. 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. 29. 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. 30. 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

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