IB-4 Monitoring & Measuring Flashcards
Calculate the 8 hour TWA (time weighted average) for chemical exposure
exposure mg x exposure time (calculate for each task in the shift if under an hour use 0.) / 8 (8 hour shift)
explain what OEL (occupational exposure limits) means?
OEL is the maximum concentration of an airbourne substance averaged over a reference period to which employees may be exposed.
Controls personal exposure to hazardous substances / noise / vibration / radiation
Specified by a competent authority
expressed in units mg/m3 or ppm.
2 different reference time period STEL (15mins) acute ill health - LTEL (8hr) chronic ill health symptoms
State the information that should be included in a record of monitoring
- date, time, duration of monitoring
- location - what equipment / dates of calibration
- who conducted the tests / credentials
- operations in progress at the time of checks
- result - calculated exposure
- identification of relevant OEL
- assessments whether any improvements or repairs are needed
- date of last examination and test
How long should records be kept and the factors that determine this period
Depends on the measurement taken. Personal dosimeters 40 years, static sampling 5 years
Outline what is meant by biological monitoring and indicate circumstances in which such monitoring may be appropiate
Involves measurement / assessment of workplace agents (or metabolities) in tissues bodily fluids or breath. indicates how much of the chemical as entered the body
Compliments air monitoring and helps determine adequacy of existing controls
can be used when there is significant absorption by non respiratory routes & in circumstances when there is a significant reliance on PPE
Eg isocyanate can be found in urine
eg. the detection of significant levels of lead in blood
What factors need to be considered when completing a risk assessment for limestone dust
- nature of dust
- number of people exposed
- individual susceptibility
- routes of entry
- particle size
- level and duration of exposure
- work methods - power tools
- current controls
- monitoring results
Describe an overall monitoring strategy that could assess the actual exposure of toxic substances
HSG173 Monitoring strategies for toxic substances
stage 1
- establish the need for and the extent of exposure monitoring
- what are the potential risks - is more information needed
a) information gathering
b) simple qualitative tests
stage 2
- estimate the employees personal exposure and the effectiveness of controls
- identify the groups most likely to be exposed and the conditions & factors which give rise to this exposure
- use semi quantative methods or full quantative laboratory based sampling & analysis
- personal sampling / anemoters for LEV / static sampling /stain tubes / direct reading instruments
stage 3
- dealing with carcinogens / mutagens / respiratory sensitisers
- exposure is highly variable between employees doing the same task
- complex process
- step 1&2 indicate concentrations are close to OEL or that additional controls need to be justified
- mutagens and carcinogens
what are the advantages & disadvantages of biological monitoring
advantages
- it can help demonstrate if PPE & engineering controls and effective
- it measures individual exposure to a chemical by all routes of entry
- it identifies what has been absorbed by the body
- it shows how effective improvements in control measures have been
- it provides reassurance to workers that their individual exposure is being monitored
disadvantages
- sampling may require blood to be taken which requires a nurse of physician - suitable facilities & can be costly
- confidentiality and data protection
- aims to protect the majority of the population - an individual may suffer adverse changes below the concentration level published
- need informed consent
- avoid sample contamination
if no agreed technique exists or recognised standard then there is no point in conducting biological monitoring
what are direct reading instruments, and the advantages and disadvantages of using these
they measure the concentration of chemicals in the air and quantify the concentration of the contaminant. they can monitor data and trigger alarms
eg. photoionisation detector PID
advantages
- can continually monitor the air
- can be specific to a given substance
- immediate readings
- identifies periods of peak concentration
- can be connected to a chart or data logger
disadvantages
- an be expensive
- need a competent technician
- need to be calibrated
- can be influenced by mixtures
what is a stain tube detector and how does it work
they are a type of colourimetric direct reading instrument that provides a convenient method of analysing gas & vapour contaminant in the air. grab sampling - point in time.
a known volume of air is drawn into the tube by using a specifed number of strokes counted by a stroke counter. the contaminant reacts with the agent in the tube and a coloured stain is produced
what are the limitation of using a stain tube detector to analysis the gas or vapour contaminant in the air
- in correct broken ends can effect the flow rate
- bellows must be fully actioned for each stroke
- possibility of cross sensitivity
- problems caused by variations in pressure and temperature
- shelf life of reagent tubes
- grab sample only a point in time measurement
what is the general principle for sampling for solid particles (gravimetric analysis of dust)
- contaminated air is drawn in through a filter held inside the sampler
- the filter is weighed before and after sampling (accurately using laboratory scales)
- the weight of the dust collected is used to calculate the dust concentration in the air in mg m3
the sampling equipment consists of - air pump - hose - sampler (small filter) - flow meter (used to check the flow rate of the sampler)
Outline the qualitative tests which can be done to identify management of dusts
- Tyndall beam - shows air movement
- Dust lamps - makes fine dust visible & helps identify emission sources
- smell and sight
what is phase contrast microscopy
used to count the number of asbestos fibres collected on the filter.
once the slide has been cleared (acetone vapour) the slide is viewed on a phased contrast light microscope. that allows the fibres to be distinguished from the background
Outline what information is needed
about chemical exposure (HSG173 initial appraisal)
- identify the hazardous properties of the chemicals exposed
- identify the routes of attack
- where in the process is exposure likely to occur
- number, type & position of emission sources
- groups of individuals likely to be exposed
- qualitative methods
- likely patterns and duration of exposure
- existing control measures in place
