B4-MONITORING AND MEASURING Flashcards
Five employees work an 8 hour shift during which they are exposed to a hazardous dust.
The employer has asked an occupational hygienist to undertake monitoring of the employees’ personal exposure to the
hazardous dust.
(a) Describe how the hygienist should determine the employees’ long term personal exposure to the total inhalable hazardous
dust. (10)
In determining the employees’ long term personal exposure to the total inhalable
hazardous dust, the hygienist would be expected to monitor the exposure throughout
the eight hour shift and note both the work undertaken during the monitoring and the
time for which the sampling was undertaken.
A gravimetric method should be used
incorporating a pump, a filter and an appropriate sampling head such as a 7 hole, an IOM or a conical inhalable head with the head being positioned in the breathing zone
of the employee.
The pump flow rate would be calibrated and noted as would the volume of air in the sample collected, and the filter weighed before and after the sampling to determine any gain in the weight.
The concentration of total inhalable dust
could then be calculated by dividing the weight gain by the volume of air with the result
being expressed in mg/m³.
(b) The five employees were each monitored for exposure to total inhalable dust during the same 8 hour shift.
Four of the results are roughly equivalent but the fifth is significantly higher.
Outline the possible reasons for this discrepancy. (10)
the working environment and the tasks being
performed;
those resulting from possible failures with the monitoring equipment and those connected with the individual employee.
In considering the working environment,
there could have been areas in the workplace which were not as well ventilated as
others with possible problems with the local exhaust ventilation provided.
As for the monitoring equipment for the individual concerned, there could have been errors in the calibration of the pump flow, in the timing of the air measurement, in the selection of the filter and in weighing the filter at the end of the exercise either because of a mis-reading or because different and possibly uncalibrated scales were used for the rogue
sample.
The individual, too, could have had a part to play if they had been particularly
involved in the more dusty operations, had taken fewer or shorter breaks than the
other operators and had not taken sufficient care with personal hygiene and had
continued to wear dusty overalls for long periods.
Finally the possibility of deliberate sabotage could not be discounted.
A healthcare research laboratory undertakes work with hazard group 3 biological agents which require containment level 3 controls.
Outline a range of technical controls that should be used to minimise the risks to those working in the laboratory, where elimination or substitution
of the hazard is not possible. (10)
the separation of the laboratory from other activities in the same
building; passing extracted air through a HEPA (high efficiency particulate air) filter;
the provision of engineered access to be restricted to authorised persons by means of
a security pass or swipe card;
the workplace to be sealable to permit disinfection and
to be maintained at an air pressure negative to atmosphere;
all surfaces to be
impervious to water, easy to clean and impervious to acids, alkalis, solvents and disinfectants;
the provision of secure storage for the biological agents;
an observation window to be fitted so that the occupants can be seen at all times;
using a class 111
microbiological safety cabinet with sealed front and glove port access to carry out the
work;
a facility such as an autoclave to be provided for rendering waste safe
and
finally the provision of appropriate and adequate washing and toilet facilities
Outline how the personal exposure of the operative to methanol can be measured. (4)
So while existing control measures are adequate in terms of potential chronic health effects, additional control measures are required to reduce potential acute health effects from exposure
during the measuring activity.
Hierarchy of control to be applied:
eliminate (unlikely?);
Substitute (less hazardous solvent?);
isolate / enclose / automate measuring process;
install or improve LEV;
provide appropriate PPE (gloves etc - see Sk notation = skin absorption) and RPE;
additional air monitoring may be required;
health surveillance programme;
monitoring and maintenance of control
measures.
Some of the measurement principles that can be used include gravimetric analysis, microscopy and chemical
analysis.
For EACH of these measurement principles:
(a) Identify a type of hazardous substance for which it can be used AND suggest a typical workplace situation where such a measurement may be necessary. (6)
Gravimetric: used for inhalable and respirable particulates / dusts eg wood dust
(sawmill); flour dust (bakery);
respirable crystalline silica dust (quarry / stonemasons)
Microscopy: used to determine the airborne concentration of fibres eg asbestos fibres during asbestos removal / stripping
Chemical analysis: used to determine airborne concentrations of vapours, gases, fumes - eg solvent vapours during degreasing; isocyanate during car body spraying; welding fume
(b) Outline the type of equipment and the methodology used to determine the employee’s personal exposure to the hazardous substance. (14)
Equipment = pump, filter membrane, sampling head (IOM single hole, IOM 7 hole or cyclone for respirable fractions);
weigh filter before - pass known vol of air through filter via pump then re-weigh;
calculate gain in weight per vol of air = mg/m3
a sampling pump that draws air at a controlled flow rate (2.2l/min) through an acetate membrane filter which collects the fibres; the filter is housed in a sampling head (IOM) with a cowl to prevent ingress of dust particles; the sampling head should be non-conductive to avoid static charge
attracting dust/ fibres to the filter; following the sampling process the filter is mounted on a microscope slide marking with a grating (graticule) and the filter is dissolved leaving the fibres on the slide;
the fibres are then counted using phase contrast microscopy - only certain fibres are counted (aspect ratio 3:1 and > 5 microns);
the number of fibres and the volume of air drawn through the filter
can be used to calculate the fibre concentration (fibres / millilitre of air)
The quantification process would require the use of calibrated pumps drawing a known quantity of air through the sampling medium - eg silica, charcoal or Tenax. The contaminant is adsorbed onto the sampling medium and sent for laboratory analysis whereby the contaminant is de-sorbed and
analysed via techniques such as infrared or mass spectrometry, or gas-liquid chromatography.
This identifies it and the concentration of each of the airborne contaminants can be calculated.
(a) Give the meaning of the term biological monitoring. (2)
Biological monitoring is the measurement / assessment of hazardous substances or their
metabolites in tissues, secretions, excreta or expired air and is complementary to air monitoring.
(b) Outline the circumstances in which biological monitoring may be appropriate. (4)
BM is appropriate:
• where required by law - CLAWR eg Lead exposures - blood / urine lead levels monitored;
COSHH / EH40 - BMGVs Carbon monoxide 30 ppm carbon monoxide in end-tidal breath -
Post shift; Chromium VI 10 μmol chromium/mol creatinine in urine - Post shift; Isocyanate 1 μmol urinary diamine/mol creatinine in urine
- Post task; Lindane 35 nmol/L (10 μg/L) of
lindane in whole blood (= 70 nmol/L of lindane in plasma) – Random - where there is a risk of significant absorption through non-respiratory routes - esp. skin
- where there is significant reliance on PPE
- where there is a valid technique for measuring exposure / body burden
- in order to evaluate the effectiveness of existing control measures
- where there is a specified BMGV
- as part of a health surveillance programme
- where there is a need for information on accumulated dose
(c) Outline the practical difficulties that an employer must take into account when introducing a
programme of biological monitoring. (4)
Practical difficulties include:
gaining informed consent - dealing with objections / concerns / fears - ethical / phobias / suspicion
etc;
expensive / time consuming - staffing problems / cover (post-shift / task / random);
requires specialist (medical) expertise;
requires special facilities - hygiene etc;
maintaining sample integrity -
avoiding cross-contamination / cross-infection;
maintaining personal records over long periods - 40 / 50 years / confidentiality issues;
dealing with “over-exposed” persons - change of duties / suspension / counselling
Five employees work an 8 hour shift during which they are exposed to a hazardous dust.
The employer has asked an occupational hygienist to undertake monitoring of the employees’ personal exposure to the hazardous dust.
(a) Describe how the hygienist should determine the employees’ long term personal exposure to the total inhalable hazardous dust. (10)
Personal exposure to total inhalable dust should be carried out by:
Monitoring throughout an 8 hour shift;
keeping a record of activities involved;
noting the time / duration of sampling;
use an approved gravimetric method - MDHS 14/3;
calibrated pump (2.2l/min;
sample head (IOM / 7 hole / conical);
filter (pre-weighed);
sample head in breathing zone (within
30cm - eg lapel);
pump air through filter at specified flow rate for specified time period (8 hour?);
check flow calibration;
collect filter / cartridge and send to be weighed (calibrated scales / approved / accredited laboratory);
calculate weight gain and determine volume of air drawn through pump during
sampling period;
calculate concentration of dust in air (weight gain / volume = milligrams of dust per
cubic metre of air = mg/m3)
(b) The five employees were each monitored for exposure to total inhalable dust during the same 8 hour shift.
Four of the results are roughly equivalent but the fifth is significantly higher. Outline the
possible reasons for this apparent discrepancy. (10)
Apparent discrepancy in the fifth result could be associated with
(i) the working environment - person works in dustier area, different air movement patterns / ventilation,variability in effectiveness of LEV
in sampling area;
(ii) the tasks being carried out - person does different / dustier tasks to others, uses
different equipment or adopts a different work routine / posture / shorter breaks etc;
(iii) the monitoring equipment - defects, false readings, wrong calibration, wrong filter, misreading results, errors in weighing etc;
(iv) the individual involved - poor hygiene, dusty clothing; sabotage
(b) Explain THREE of the “principles of good practice” that should be considered when deciding if the control of exposure can be treated as “adequate” under the COSHH regulations (3)
COSHH principles of good practice include requirements to:
design and operate processes and activities to minimise emission;
take into account all relevant routes of exposure not just inhalation;
periodically check and review control measures to ensure their continuing effectiveness;
identify occasions when personal protective equipment may have to be used alongside other control measures;
provide information and training to employees;
avoid increasing the overall risk to health
and safety by the introduction of selected control measures.
In a manufacturing process, operators use a range of solvents.
Describe a monitoring strategy that
could be used to measure the exposure of the operators to solvent vapours. (10)
The exposure of workers should be assessed in accordance with any procedures set out in the relevant MDHS.
A 3 stage monitoring strategy should be adopted (see “Monitoring strategies for
toxic substances” HSG 173):
(1) initial appraisal;
(2) basic survey;
(3) detailed survey Initial appraisal (qualitative):
should take account of the nature of the solvents and their hazard
categories - toxic, harmful, irritant, carcinogenic etc;
their physical & chemical properties - volatility and ambient temperatures;
potential health effects;
routes of entry;
synergistic / additive effects;
working patterns / duration of use / frequency of use;
numbers and categories of person exposed -
vulnerable / susceptible groups;
occupational exposure limits - WELs and BMGVs;
effectiveness of existing control measures (eg LEV).
The outcome of the initial appraisal provides a basis for deciding whether exposure is likely to be significant and whether a basic / detailed survey and exposure monitoring should be carried out.
Basic / detailed survey (quantitative):
use of static and / or personal monitoring techniques to measure airborne concentrations via passive (colorimetric badges / stain tubes) or active devices,
direct reading instruments or laboratory analysis (eg calibrated pumps draw a known quantity of air through a sampling medium - eg silica, charcoal or Tenax;
the contaminant is adsorbed onto the
sampling medium and sent for laboratory analysis;
the contaminant is de-sorbed and analysed via techniques such as infrared or mass spectrometry, or gas-liquid chromatography);
biological monitoring also required - analysis of solvent levels in blood / urine / exhaled breath to estimate “body burden” (amount absorbed into body) - this is particularly important for solvents, where
exposure may also occur via skin absorption and / or ingestion ie airborne concentration (exposure by inhalation) is only one consideration.
This identifies it and the concentration of each of the airborne contaminants can be calculated.
Comment: some candidates focussed on control measures that should be applied, LEV efficiency and dust monitoring
Describe the approach that is followed when setting a workplace exposure limit (WEL) for a hazardous substance used in the workplace. (8)
WEL set by ACTS (Advisory Committee on Toxic Substances), following a review of toxicological & epidemiological data by WATCH (Working Group on Action to Control Chemicals).
If NOAEL defined then WEL should be below NOAEL;
if there is no NOAEL then WEL should be set at a level that represents good occ hygiene practice within the industry sector.
WEL should take account of
reasonable practicability - ie the cost , effort, inconvenience and practicality as against risk / severity of potential health effects.
Personal dust monitoring has been carried out on five employees, all of whom work in the same factory area where dust is released.
The five employees were sampled at the same time and for equal duration.
Four of the results are roughly equivalent but the fifth is significantly higher.
Outline the possible reasons for this apparent discrepancy. (10)
(i) the working environment - person works in dustier area, different air movement patterns / ventilation,variability in effectiveness of LEV
in sampling area;
(ii) the tasks being carried out - person does different / dustier tasks to others, uses
different equipment or adopts a different work routine / posture / shorter breaks etc;
(iii) the monitoring equipment - defects, false readings, wrong calibration, wrong filter, misreading results, errors in weighing etc;
(iv) the individual involved - poor hygiene, dusty clothing; sabotage
(a) Explain the meaning of the following terms:
i) Chemical Abstract Services CAS number (2
(a) (i) CAS number = a unique internationally recognised identifying number allocated to a particular chemical so as to avoid confusion with other similarly named substances (similar to ISBN for books)
(a) Explain the meaning of the following terms:
ii) Workplace Exposure Limit (2
WEL = the maximum concentration of an airborne substance to which a person may be exposed by inhalation
(a) Explain the meaning of the following terms:
iii) Long-term Exposure Limit (8 hour TWA reference period) (2
LTEL is the airborne concentration (in mg/m3 or ppm) measured as an 8 hour time-weighted
average - representing a working shift
(a) Explain the meaning of the following terms:
iv) Biological monitoring guidance value (Bmgv) (2
BMGV is a value specified in EH40 in relation to hazardous substances where significant
exposure may occur by routes other than inhalation – skin absorption or ingestion (eg lead).
There are two types of BMGV - a Health Guidance value (HGV) which represents a level at which there are no adverse effects on health
– and a Benchmark Guidance Value (BGV) which should not normally
be exceeded.
BMGVs are measured in terms of the concentration of a hazardous substance or its
metabolite present in an exposed person’s blood, urine or exhaled breath.
www.hse.gov.uk/coshh/table2.pdf
(b) Describe the physiological effects of carbon monoxide on the body and identify the symptoms that may be experienced by exposed persons. (6)
CO is inhaled into the lungs where it passes into the bloodstream, displaces oxygen and
combines with haemoglobin to form carboxy-haemoglobin;
as this is a relatively stable chemical
combination which is only slowly displaced from the blood stream it reduces the capacity of the blood to carry oxygen to the brain, vital organs and body tissues.
Resulting symptoms include fatigue, loss of concentration, disorientation, headaches, nausea, dizziness, breathlessness, collapse and ultimately death.
(c) Outline the control measures that could be used to reduce exposure to carbon monoxide in a motor vehicle repair premises. (6)
Exposure to CO in a MVR workshop can be reduced by providing suitable LEV (connected to exhaust system);
reducing the duration of engine running tests etc;
carrying out work outside;
providing natural ventilation of work area / vehicle pits;
monitoring airborne CO levels;
health surveillance - biological monitoring (exhaled breath);
installing CO monitors / alarms;
providing relevant training and information;
segregating test areas from customer facilities.
(a) The term Workplace Exposure Limit (WEL) is defined in the Control of Substances Hazardous to Health (COSHH) Amendment Regulations 2004. Explain what this term means in practice. (3)
WEL = the airborne concentration of a hazardous substance, measured as a time weighted average, above which a person may not be exposed by inhalation.
WELs are listed in EH40 and measured in mg/m3 or ppm over an 8 hour TWA (LTEL) and / or a 15 min TWA (STEL).
In a manufacturing process workers use a range of solvents.
(a) Outline the issues that should be considered and the information that should be consulted when preparing a COSHH risk assessment for this situation. (6)
Issues include: nature of solvents / hazard categories / physical & chemical properties;
health effects;
routes of entry;
synergistic / additive effects; working patterns / duration of use /
frequency of use;
numbers and categories of person exposed - vulnerable / susceptible groups.
Information to be consulted includes: COSHH 2002 / ACoP;
CHIP regs / Approved Supply List;
hazard labels / SDS - risk / safety phrases;
HSG 173 - Monitoring strategies for toxic substances;
EH40 - WELs & BMGVs;
chemical abstract service (CAS);
MDHS.
