Atmospheric monitoring Flashcards
What is a personal sampler
Attached to the person
What is a static sampler
positioned in work area
continuous sampling
mains or battery powered pumps
What document details standard methods of sampling
MDHS series - methods for determination of hazardous substances
Short term sampling
spot, snap or gran sampling
take immediate sample of air, pass through a chemical agent that responds to chemical being monitored
or direct reading instrument
Long term sampling
personal or static samplers
Considerations for sampling strategy / method
type of air contamination from initial appraisal
people affected - representative group or random sampling
frequency of measuring - depends on hazard, acute / chronic effects, exposure limits, previous results
technique - depends on hazard, purpose of sample
measurement for chronic hazard
continuous personal dose measurement
spot readings at selected locations / times
measurement for acute hazard
continuous rapid response personal monitoring
spot readings at selected locations / times
measurement for safe entry
direct reading instrument
direct reading instrument examples
combustible gas detector
oxygen meter
ultraviolet photo ionisation detector (PID)
advantages of direct reading instrument
info at time of sampling
quick detection
disadvantages of direct reading instrument
only measure specific chemical classes
not designed for less than 1 ppm
can be affected by other substances - false readings
need to be operated by qualified person
reasons for atmosphere monitoring
health risk assessment compliance with WELs help design controls check effectiveness of controls info for employees indicate need for health surveillance establish in house standards
Info sources
labels on containers safety data sheets HSE publications technical info from trade assocs accident records health surveillance records absence rates staff complaints
stain tubes
contain inert material with reagent for substance being tested for
glass tubes
passive or via pump (manual or powered)
advantages of stain tubes
easy to use
easy to read
wide range of tubes available
low cost
disadvantages of stain tubes
limited shelf life false reading from other chemicals safe disposal issues limited accuracy depends on skill of operator
bags & canisters
evacuate air before use
use where constant concentration
bag is chemically inert
sent to lab for analysis
Tyndall lamp
light that shows dust floating in the air
factors influencing health effects of dust
nature of the dust
particle size
exposure time
airborne concentration
where is the breathing zone
300 mm in front of and around face
dust filtration sampling system
filter suitable for dust being sampled
sampling head - holds the filter, prevents problems ref wind
tubing
pump - to maintain smooth flow at required rate, light for personal sampling system
types of sampling head
protected
cyclone
cowl head
protected head sampler
no problems ref orientation or wind speed
best in workplace conditions
cyclone head sampler
cyclones simulate nose / mouth
used for respirable dust sampling
cowl head sampler
for fibre sampling
open faced filter
cowl faces downwards
types of sampling pump
piston / compressed chamber
rotary vane
diaphragm
piston / compressed chamber pump
volume depends on number of pump strokes
relies on manual operation
cannot be used for dust sampling
rotary vane pump
flow rate measured with integral flow meter
sample volume = flow rate x time
diaphragm pump
sample volume = number of diaphragm moves
other pump considerations
dust explosion risk, therefore must not be source of electrical ignition
battery capacity
serviced regularly
pump cleaning
filter types
paper - cheap but absorb water
glass fibre - cheap, high particle retention but shed fibres
silver - low chemical interference but expensive
plastic membrane - good for use with microscope but high static, poor dust adhesion
PVC - low chemical interference but high static, poor dust adhesion
filter weighing
pre-weighed and weighed again after sampling
matched weight - contains 2 filters but only one collects dust. Both weighed at lab
MDHS dust sampling method
decide on sample head select clean dry head fit with required filter attach to pump have blank samplers available use blanks as control attach to worker with head in breathing zone check often for correct operation at end, record flow rate and duration fit protective cover over head and remove from worker remove filter and send for analysis
dust measuring analysis
gravimetric
physical
chemical
gravimetric analysis
measure weight of dust collected
weigh filter before and after
calibrated weighing device
calculate dust concentration
physical analysis
techniques inc xray fluorescence spectroscopy xray diffraction infra red atomic absorption
chemical analysis
analysis of metal dusts
fibre analysis
use microscope
difficult to accurately count fibres
use phase contrast microscope to help see fibres - enhances contrast of fibres on filter
use polarising filters also
passive personal samplers
no pump some change colour to indicate contamination light easy to use activated charcoal to collect solvents
active personal samplers
worn by worker
pump fitted to belt
tube attached near to collar
activated charcoal tubes
absorbs vapours
tube sealed with plastic caps
sent off for analysis
sampling technique requirements
minimum 75% collection efficiency for contaminant being tested for
collect enough to analyse
collection means compatible with analysis technique
minimum on-site preparation
equipment / technique does not create a hazard to worker
vapour analysis techniques
remove contaminant from material that absorbed it
use solvent (carbon disulphide) or heat to desorbe into gas
analyse vapour
types of vapour analysis
infrared spectrometry - used for organic chemicals
ultraviolet spectrometry - metals
atomic absorption spectrometry - determines actual concentration levels
chromatography - colour separation of substances in mixtures
gas liquid chromatography - solid / liquid vapourised and separated in an inert gas stream
xray diffraction - xrays diffracted when pass through substance, diffraction pattern analysed
formula for dust concentration
weight gain in filter divided by total volume of air sampled
mg / m3
advantages of Tyndall lamp
very fine dust not visible to naked eye, lamp shows this up can see source of dust use as first stage analysis qualitative technique easy to use minimal training needed
disadvantages of Tyndall lamp
provides immediate info only
does not measure particle size
