B4 Ollie Flashcards
Workplace Exposure Limits (1)
Airborne concentrations , averaged overtime, which according to current knowledge are thought to be safe
Published every year in HSE
Environmental lHealth EH40
Substances are allocated a WEL in either parts per million (ppm) or milligrams per cubic metre (mg/m3)
Basis for determining compliance with COSHH Regulations
Workplace Exposure Limits (2)
WELs MUST not be exceeded
Principles require that reduction below WEL to be proportionate to the health risk
Some WELs must be must be reduced to a level as low as reasonably practicable :
Carcinogens and mutagens (R45, R46, R49)
Respiratory sensitisers (R42, R43)
Lack of WEL does not mean substance is safe
Workplace Exposure Limits - WATCH & ACTS
WATCH:
Working Group on Action to Control Chemicals
Reviews scientific evidence and publishes risk assessments
Scientific evidence includes epidemiological studies /animal testing etc
ACTS:
Advisory Committee on Toxic Substances
Considers evidence and takes into account socio-economic factors Makes recommendation to HSE
Workplace Exposure Limits - First & Second Level
First: Set at a level where there is no adverse affects on human health(NOAEL) - exceptions : Genotoxic carcinogens Asthmagens Mixtures Lackof data If not reasonably practicable
Second:
Set at a level that is considered to represent good control
Workplace Expos ure Limits - 8Hour TWA
Represent an average level of exposure measured over an eight hour working shift
Calculated by:
8 hour TWA=C1T1+ C2T2+ C3T3……divided by 8 hour period
C = Concentration
T = Time (hours )
Role of the Occupational Hygienist
Usually trained to Degree level, and preferably a member of British Occupational Hygiene Society (BOHS)
Identification of occupational health hazards
The measurement and evaluation of exposure to hazards Interpretation of results
The design of control measures
Education and training of workers and management
Preparation of labels and keeping of records Conducting research
Why Measure Airborne Contaminants ?
Risk assessment To ensure compliance with WELs To determine design of control measures To check effectiveness of controls To indicate the need for health surveillance To establish in-house standards Insurance Legal requirement
Legal Requirements
COSHHReg 10:
If risk assessment indicates that it is requisite for ensuring maintenance of adequate control
COSHH Schedule 5:
VCM continuous , chromium electrolysis every 14 days
CAR:
If likely to exceed control limit (0.1f/cm3 of average air over 4hr period)
CLAW:
Every 3 months if exposure likely to be significant (lead other than lead alkyls 0.15mg/m3 & lead alkyls 0.10mg/m3)
Types of Monitoring
Static sampling
Personal monitoring
Monitoring Strategy (HSG173)
Initial Appraisal:
If exposure not under control - move to
Basic Survey:
Evaluate results - if more information is required or conclusion not certain - move to
Detailed Survey:
Following conclusions - carry out reappraisal & monitoring
Initial Appraisal
Enables you to decide on risks and hazards
Enables you to decide if monitoring is required
Consider:
Substance, physical properties , points of exposure, number and nature of release points , pattern and degree of exposure, WELs
Sources of information:
Labels , safety data sheets , HSE publications , technical literature, experience etc
Simple qualitative tests:
Smoke tubes , dust lamp (MDHS 82), odour
Methods for the Determination of Hazardous Substances
Series of publications from HSE
Provide standard methods for analysis
Currently 125 methods
Can be downloaded from HSE website
Examples:
MDHS14/3: General methods for sampling and gravimetric analysis of respirable and inhalable dust
MDHS 82: The dust lamp, a simple tool for observing the presence of airborne particles
Basic Survey (1)
Estimates exposure, estimates efficiency of engineering controls
Needed if:
There is an exposure risk and level uncertain Major changes made since last assessment
Unusual operations planned (e.g. maintenance)
New process/WEL
Basic Survey (2)
Estimates personal exposure, estimates efficiency of engineering controls
Uses semi-quantitative methods: Indicator (Draeger)tubes Computer exposure monitoring Photoionisation Detectors Flame Ionisation Detectors Portable Gas Chromatographs Infra-red Analysers
Detailed Survey
If the extent cannot be determined by the basic survey
Exposure highly variable between employees Carcinogens or senstisers involved
If BS indicates close to WEL and cost not justified Complex and usually involves occupational hygienists Quantitative methods e.g. personal samplers
May need to include biological monitoring
Factors Affecting Airborne Contaminant Exposure
Physical and chemical properties
Number of sources
Rate, duration and release from each source
Arrangement of the process , temperature and design of control measures
Dispersion or mixing due to air movements /gdv Proximity/frequency of employee exposure to source If employee has control/poor appreciation
Factors Affecting the Design of Monitoring Strategies
Health effect e.g. chronic or acute Grouping of employees: Similarly ExposedGroups (SEGs) Type of measurement: Personal or static, representative or worst-case Duration: Depends on variables in exposure e.g. 25% of shift Sampling equipment: Heavy, battery life etc Accreditation/ quality control : NAMAS, WASP, MDHS
Reappraisal/Routine monitoring
Reappraisal: Change in process Change in number of personnel Routine monitoring: To ensure controls remain effective Specific requirement e.g. VCM continuous (COSHH Schedule 5) COSHH Regulation 10
Monitoring Techniques
Gases & Vapours Dusts
Fibres
Collection of Samples
Grab Samples:
Collection of single sample
No pump or known collection rate
Qualitative
Continuous samples:
Known amount of contaminated air collected at known rate for known time
Quantitative
Can be static of personal
Calibrated pump, flow meter, appropriate sampling device
Known as sampling train
Collection of Gases and Vapours - Grab Samplers
Gases collected and sent to laboratory for analysis
Grab Samplers:
Evacuated flasks
Gas /liquid dis placement containers Plastic containers,Syringes
Collection of Gas es and Vapours - Continuous
Continuous samplers:
Means of collection using calibrated pump
Liquid (midget) impingers
Air containing gas /vapour drawn through liquid using calibrated pump
Gas /vapour dissolves in liquid e.g.
Methanol vapour/water Impinger can be worn on lapel
Collection of Gas es and Vapours - Adsorption Tubes (1)
Tubes of glass or stainless steel
Approximately 7cm in length, 6 mm diameter
Adsorbent:
Activated charcoal, e.g. used for hydrocarbons
Silica gel, e.g. used for phenol
Calibrated pump draws known volume of air across charcoal at known rate and known time (e.g. 4 hours )
Collection of Gas es and Vapours - Adsorption Tubes (1)
Contaminant binds to charcoal - more than 20%in second chamber represents sample loss
Ends capped and transported to laboratory
Contaminant released from charcoal with carbon disulphide (solvent) or thermally
Chemical analysis of contaminant carried out
Collection of Gases and Vapours - Passive Samplers (1)
Usually take the form of a badge containing the adsorbent
No pump required
Chemicals diffuse from the atmosphere in to the sampler at a fixed rate
Seal broken on sampler at s tart and worn or fixed time
Re-sealed and sent for analysis
Concentration in air can be calculated from the quantity adsorbed
Analysis of Collected Samples - Chromatography
Method for separation of mixtures of substances
Principle:
Mixture dissolved in mobile phase
Passed through a stationary phase
Substance in mixture adsorb to stationary phase at different rates
Example:
Paper chromatography
Mobile phase solvent
Stationary phase paper
Analysis of Collected Samples - Spectroscopy
Technically the study of the interaction between matter and radiated energy
Analytical techniques referred to as spectrometry:
Infra-red absorption spectrometry
Atomic absorption spectrometry Mass spectrometry
Analysis of Collected Samples - Infra Red Spectroscopy
Principle:
Measures the way that infra-red radiation is absorbed by a sample
So-called patterns or bands of absorption are characteristic of particular chemical bonds
Can be used to identify unknown chemicals e.g. Hydrocarbons , chlorinated hydrocarbons
Analysis of Collected Samples - Atomic Absorption Spectrometry
Principle:
Measures the way that infra-red radiation is absorbed by a sample
So-called patterns or bands of absorption are characteristic of particular chemical bonds
Can be used to identify unknown chemicals e.g. Hydrocarbons , chlorinated hydrocarbons
Analysis of Collected Samples - Atomic Absorption Spectrometry
Principle:
Sample is raised to a higher energy status by heating in flame
The amount and wave length of energy absorbed can be measured
Wave length characteristic of particular substance
Used for metals e.g. Lead, cadmium, copper
Analysis of Collected Samples - Mass Spectrometry
Principle:
Substance is ionised, generating charged molecules /ions
These are passed through electromagnetic fields causing deflection of these ions
The amount of deflection is related to the mass and structure of the molecule
Frequently used with GC (GC-MS)
Used to identify and quantify range of molecules , e.g. Hydrocarbons , biological molecules , drugs
Collection of Gas es and Vapours - Direct Reading
Instruments
Available for a range of substances and include:
Infra-red gas analys er (e.g. ammonia, carbon monoxide, s tyrene, toluene) Photoionis ation detectors (PID)
Flame ionis ation detectors
Oxygen electrodes
Collection of Gas es and Vapours - Stain-indicator Tubes (Drager Tubes /Colour-metric Detectors ) - Advantages
Relatively cheap Can be used with little or no specialist training A wide range of tubes are available Results are easy to interpret Give an (almost) immediate reading No power source required Inaccurate (typically + or - 20%)
Collection of Gases and Vapours - Stain-indicator Tubes (Drager Tubes /Colour-metric Detectors ) - Limitations
Often subject to interference by similar substances
Can only be used if the identity of the contaminant is known Broken glass can be a hazard
Temperature and humidity sensitive
Limited shelf life
Usually small sample volume
Collection of Particulates
Dusts , fibres , fume
Total inhalable dust
Respirable dust (< 7 microns aerodynamic diameter) Fume
Gravimeter analysis: Collect particulate and weigh using sensitive balance Continuous sampling: Calibrated pump Flow device Sampling device Known flow-rate for known time Particulate in air can be calculated
Collection of Particulates
IOM Sampler for Total Inhalable Dust
Collection of Particulates - Samplers for Total Inhalable Dust
Most commonly used :
IOM Sampler 25mm diameter filter
Face protected with cover plate (protected face head)
Also useful for collecting metal fume e.g. lead, cadmium
One problem is uneven distribution of dust on filter
Air flow rates typically 2.0 litres /min for 4 hours
Collection of Particulates - Respirable Dust
Dust < 7 micrometers
Relates to aerodynamic diameter so simple filters not suitable
Usually collected using a cyclone preselector
Large particles pass into grit-pot
Smaller particles collect on pre- weighed filter
Attached to calibrated pump at known rate for known time
Collection of Particulates -Asbestos and Other Fibres
Cowled head sampler used
Ensures even spread of fibres on filter
Gridded, clearable filter used
Attached to calibrated pump for at known rate for known time
Filters removed, cleared in propanone (acetone) and observed under phase-contras t microscope
Fibres manually counted
Asbestos Fibre Counting
The diameter of micros cope field is known
The number of fibres in 100 fields is counted
The counter can identify asbestos fibres
If the full fibre cannot be seen counts as half a fibre
Can therefore es timate the number of fibres on the filter
From pump flow-rate and time can then calculate the number of fibres/ml
Factors to Consider in the Hygienists Report
Competence of author/service provider Methods employed (e.g. MDHS) Quality control (e.g. NAMAS) Strategy employed (e.g. Number of samples , personal monitoring) Substances measured Conclusions
Biological Monitoring
Measurement and assessment of hazardous substances or their metabolites in tissues ,secretions ,excretaor expired air:
Blood e.g. Lead
Urine e.g. Hexavalentchromium
Breath e.g. Carbon monoxide
Biological Monitoring - Advantages
Gives measurement of amount accumulated, not theoretical amount
Gives indication of direct effects
Allows for variations in individuals (size,weight,gender etc)
Takes into account metabolites
Can show damage from other routes of entry Can. show if controls are working
Biological Monitoring - Disadvantages
May be intrusive e.g. blood samples Not always possible(e.g.asbestos)
Expensive,Expertise needed to interpret results
Reactive rather than proactive
Subject to time factors
May be affected by diet & other external lifestyle factors Limited methods
Biological Monitoring - BMGVs
EH40:
Biological Monitoring Guidance Values (BMGVs ) – non statutory
CLAW Reg 10 :
Biological monitoring required if lead exposure significant
Every 3 months for young person or woman of reproductive capacity
Every 6 months for others
Medical surveillance
Blood-lead level concentration
General employees:
Blood Action Level - 50um/dl
Suspension Level -60um/dl
Women capable of having children:
Blood Action Level - 25um/dl
Suspension Level -30um/dl
Young persons:
Blood Action Level - 40/dl
Suspension Level - 50 um / dl
Urinary-lead level concentration
General employees:
Urine Action Level - 50 um / dl
Suspension Level - 110um/dl creatine
Women capable of having children:
Urine Action Level - 2 5u m / d l
Suspension Level - 25um/dl creatine
Young persons:
Urine Action Level - 40um/dl
Suspension Level - no figure
