04_monitoring_and_measuring_20140117153031 Flashcards
Workplace exposure limits (WELs) are
occupational exposure limits (OELs) set under the CoSHH regulations in order to help protect the health of workers
In the UK WELs are set at levels which are either:
The level at which no adverse effects on human health (NOAEL) would be expected to occur based on the known and/or predicted effects of the substance, or if this is not reasonably achievable. A level corresponding to what is considered to represent good control, taking into account the severity of the likely health hazards and the costs and efficacy of control solutions.
NOAEL is
the highest point on the exposure response curve at which there are no adverse health effects observed in humans
Control of exposure to substances hazardous to health is adequate if:
The principles of good practice set out in schedule 2A of CoSHH (page 87) have been applied WELs have not been exceeded Exposure is reduced to as low a level as is reasonably practicable for: - Carcinogens - Mutagens - Respiratory sensitisers or any other substance which the risk assessment has shown to be a potential cause of occupational asthma.
WELs apply only to people at work and to conditions where the atmospheric pressure is normal, i.e. between 900 and 1100 millibars, and WELs are expressed in the following way:
Parts per million (PPM) for gases and vapours Milligrams per cubic metre (mg/m-3) for dust, fume, airborne particles.
Short-term exposure limits (STELs)
15 minute reference period Protect against acute adverse health effects arising from brief exposures Example: eye irritation, narcosis from an alcohol based substance, irreversible tissue damage such as asbestos
Long-term exposure limits (LTELs)
8 hour reference periods Control health effects arising from prolonged or accumulated exposure Restricting the total intake by inhalation over one or more work shifts Example: ammonia, styrene, trichloroethylene
If the working exposure is less than 8 hours, the LTEL may be exceeded in proportion to the hours worked, as long as
the STEL is never exceeded
Some dusts have a specific LTEL, for example: silica dust. However, where there is no WEL assigned, dust may still be harmful, especially if it is respirable i.e. enters the alveoli. In this case CoSHH sets the WEL for ‘nuisance dust’ LTEL as:
Respirable dust = 4 mg/m3 Total inhalable dust = 10 mg/m3
Limitations to the application of exposure limits There are a number of problems associated with standard setting.
Inhalation may not be the sole route of entry into the body. Some substances have the ability to penetrate intact skin and become absorbed into the body, thus contributing to systemic toxicity. The exposure limits relate to personal monitoring. The doses received by workers may vary depending upon, for example, their work rate. A higher work rate will cause workers to breathe more deeply and inhale more air. This is not taken into consideration during standard setting … but must be taken into account during CoSHH assessment. Working conditions may impose additional stress on the body, for example: high temperatures, pressures and humidity may increase the toxic response to a substance. Errors in estimating workplace exposure could have significant effects on the controls decided upon. Toxicological knowledge may change with new knowledge.
More prescriptive risk controls lead to the introduction of the eight ‘principles of good practice’, which apply to all agents regardless of whether a substance has a WEL:
- Design and operate processes and activities to minimise emission, release and spread of substances hazardous to health. 2. Take into account all relevant routes of exposure. 3. Ensure control measures are proportionate to the health risk. 4. Choose the most effective and reliable control options to minimise the escape and spread of hazardous substances. 5. Where adequate control cannot be achieved by other means, provide, in combination with other control measures, suitable personal protective equipment (PPE). 6. Check and regularly review control measures to ensure their continuing effectiveness. 7. Inform and train all employees on the hazards and risks and the control measures developed to minimise the risks. 8. Ensure that the introduction of control measures does not increase the overall risk to health and safety.
The occupational exposure limits for lead are:
Lead (other than lead alkyls): 0.15 mg/m3 Lead alkyls: 0.10 mg/m3.
The term ‘significant’ in relation to exposure to lead is defined in Regulation 2 of CLAW as:
1) Where any employee is, or is likely to be, exposed to a concentration of lead in the atmosphere exceeding half the occupational exposure limit. 2) Where there is substantial risk of any employee ingesting lead. 3) Where there is the risk of contact between the skin and lead alkyls or other substances containing lead that can be absorbed through the skin.
Blood Lead Action level Suspension level General employee Young person under 18 Woman of child bearing age
Blood Lead Action level Suspension level 50 μg/100ml 60 μg/100ml 40 μg/100ml 50 μg/100ml 25 μg/100ml 30 μg/100ml
LTEL long term exposure limit (asbestos)
0.1f/cm3 (equivalent to 0.1 f/ml) over 4 hours
STEL long term exposure limit (asbestos)
0.6f/cm3 over 10 minutes.
Regulation 3 (application) of the Control of Asbestos Regulations (CAR) specifies that asbestos work will not need to be licensed under the following conditions:
The exposure of employees to asbestos is sporadic and of low intensity. * It is clear from the risk assessment that the exposure of any employee to asbestos will not exceed the control limit. ** The work involves: - short, non-continuous maintenance activities - removal of materials in which the asbestos fibres are firmly linked in a matrix - encapsulation or sealing of asbestos-containing materials which are in good condition - air monitoring and control, and the collection and analysis of samples to ascertain whether a specific material contains asbestos.
Sporadic and low intensity exposure (asbestos)
This applies where a suitable and sufficient risk assessment clearly shows that work does not expose workers to more than the 10 minute control period (STEL) of 0.6 fibres per cubic centimetre (0.6 f/cm3) in the air.
Monitoring of hazardous substances is necessary: 4
when failure of control measures could result in a serious health effect to demonstrate that a WEL is not being exceeded as an additional check on the effectiveness of control measures when changes in work occur that could affect employees’ exposure, for example: increase in quantity of a substance used; new systems of work or new plant.
There are different types of monitoring and equipment that may be required. These relate to the following terms. 3
Type of sampling: personal or static (environmental). Timescales: short or long term. Types of equipment: direct reading or indirect reading; active or passive air sampling.
Active air sampling
Uses a calibrated air pump to draw a known volume of air over the reagent, over a known period of time.
Passive air sampling
Allows air to diffuse over the sampling head which may be a badge, impinger / bubbler or dosimeter tube (no pump).
stages of the monitoring strategy
Initial appraisal Basic survey Detailed survey Reappraisal Routine monitoring
The initial appraisal is
Qualitative sampling methods may be used to carry out the initial appraisal, for example: Smoke tubes can illustrate the movement of air under the influence of draughts, general and local exhaust ventilation systems, and show what the effects are. A dust lamp helps to identify emission sources and watch the movement of airborne dust. Smell can also be used as an indicator of contamination, however, this is an unreliable method. If the initial appraisal were to indicate that there would be significant exposure, a basic survey would be necessary.
A basic survey is
The basic survey estimates employees’ personal exposure and provides an indication of the efficiency of process and engineering controls. It usually surveys the worst-case situations, for example: the ‘dirtiest’, or where employees have made complaints. Qualitative and semi-quantitative sampling methods can be used to estimate personal exposure. These provide a rough numerical estimate of exposure. Some semi-quantitative methods are comparatively inexpensive and easy to use, for example: chemical indicator tubes or dust lamps.
Some semi-quantitative methods are comparatively inexpensive and easy to use, for example:
chemical indicator tubes or dust lamps.
The basic survey may highlight defects and deficiencies in control strategies. If the conclusion is not certain, there will be two choices:
(1) To carry out a more detailed survey and take remedial action as necessary. (2) Take direct action to control exposure.
A detailed survey may be required when:
The extent and pattern of exposure cannot be confidently assessed by a basic survey. Exposure is highly variable between employees doing similar tasks. Carcinogenic substances, respiratory sensitisers or mutagens are involved. Undertaking major maintenance and one-off jobs, such as plant decommissioning The initial appraisal and basic survey suggest that: - the time-weighted personal exposure may be very close to the WEL - the cost of additional control measures cannot be justified without evidence of the extent of exposure variability.
A detailed survey would have a greater emphasis on personal sampling over longer periods of time, and the taking of a greater number of samples over a wider range of conditions. More sophisticated quantitative sampling methods and equipment would be used, for example:
those reliant on laboratory analysis and biological monitoring
A detailed survey will require an in-depth investigation of the process, and its environment, including: 11
Existing CoSHH assessments. Procedures and work methods. Maintenance procedures. Existing control measures and their suitability, For example: the results of the annual examination and testing of the local exhaust ventilation could be compared with its commissioning data. Existing PPE provided and its suitability. For example: the comparison of the chemical resistance of gloves against information contained in material safety data sheets (MSDS). Workplace exposure limits, with a comparison between actual exposures from personal sampling to the relevant WELs Results of biological monitoring and those of biological monitoring guidance values (BMGV). Previous environmental monitoring results. Results of health surveillance programmes. Information and instruction provided to the employees for carrying out the tasks involved. Training provided to employees.
A reappraisal is
an assessment to determine whether changes to control measures have had a positive effect.
Schedule 5 of the CoSHH Regulations requires continuous monitoring for the following chemical exposures:
Vinyl chloride monomer. Hexavalent chromium: every 14 days for sprays given off from vessels during electroplating processes.
Factors which influence the release and airborne concentration of substances include: 7
Physical and chemical properties of the substance, for example: vapour pressure, boiling point and particle size. The number of sources from which the substance is released. Rate, duration and speed of release from each source. Arrangement of the process, temperature and design of the control measures. Variations in the process, job and tasks being carried out, for example: hour, day or even week. Dispersion or mixing of the substance in the workplace air due to general or local ventilation. Ambient conditions (temperature, pressure and humidity).
From the exposure monitoring results the following conclusions may be made: 4
The data is, or is not, adequate and/or representative of all those exposed. Compliance with WELs, etc. has, or has not, been achieved. Further actions are, or are not, necessary to prevent or reduce exposure. More monitoring is, or is not, needed.
Qualitative methods are
simple observational techniques that do not involve any quantified measurement. They rely on judgment, knowledge and experience. The threshold of smell and the Tyndall light beam are examples of qualitative sampling methods.
The strengths of using stain detector tubes
Relatively cheap. Simple to use – no major costs for training or expertise. Direct reading – immediate result. Provides an indication of the need for more sophisticated measurement.
The weaknesses of using stain detector tubes
Substance specific – the correct tube must be specified for the suspected contaminant. Only suitable for chemical contaminants (gases and fume). Not very accurate – variables include: bellows efficiency wrong number of pumps cross sensitivity and date sensitivity of tubes sampling point – proximity to contaminant. A grab sample may miss the presence of the contaminant.
Qualitative sampling methods (examples)
Threshold of smell Tyndall light beam
Semi-qualitative sampling methods (examples)
stain detector tube
Personal monitoring sampling apparatus consists of:
a sampling head, positioned in the wearers breathing zone (clipped to collar, for example), connected with tubing to a calibrated portable medium flow pump (powered by rechargeable battery) and clipped to a belt or carried in a holster
There are four types of sampling head recommended for particulate sampling:
IOM sampling head, multi-orifice total inhalable sampler, conical inhalable sampler and respirable dust cyclone sampler.
The process for taking a personal sample is as follows: 11
(1) A filter is dried out in a clean area and weighed. (2) The sampling head is cleaned before use. (3) The pre-weighed filter is placed in a sampling head in a clean, dust-free environment. (4) Each sampler is labelled so that it can be uniquely identified and sealed with its protective cover, or plug, to prevent contamination. (5) The volumetric flow rate is set, for example: two litres per minute (±0.1 litre/min). (6) Each loaded sampler is connected to a sampling pump, ensuring that no leaks can occur. (7) The protective cover from the sampler is removed. (8) The sampling pump is then switched on, and attached to a calibrated flow meter so that it measures the flow through the sampler’s inlet orifice(s). (9) Air is drawn through the filter over a known period of time, for example: 4 hours. (10) The filter is then sent to an approved laboratory to be dried out again for gravimetric analysis. (11) The filter is re-weighed.
The volume of air passing through the sampler is calculated by
multiplying the mean volumetric flow rate in cubic metres per minute by the sampling time in minutes
Average dust concentration (mg/m3) =
The net weight gain (mg) of the sample substrate is divided by the volume of air sampled (m3)
The strengths of personal dust sampling are
AccurateIndicates the workers actual exposure during real work activity Allows direct comparison to workplace exposure limits (WEL) Can be used to identify a chemical
The weaknesses of personal dust sampling are
ExpensiveRequires expertise to set up Time consuming (sample to lab for analysis) May be tampered with by wearer
Spectrometry, spectroscopy and chromatography are
analysis techniques that can identify both the chemical and its concentration
Spectrometry
measures the intensity of light in a part of the spectrum specially transmitted or emitted by particular substances. This is measured using a spectrophotometer.
Spectroscopy
Spectroscopy is concerned with the investigation and measurement spectra produced when matter interacts with or emits electromagnetic radiation. It relates to the dispersion of an object’s light into its component colors (i.e. energies). By performing this dissection and analysis of an object’s light, analysts can infer the physical properties of that object, for example: temperature, mass, luminosity and composition.
Chromatography
Chromatography is the separation of a mixture by passing it in solution or suspension, or as a vapour (as in gas chromatography), through a medium in which the components move at different rates. The mixture is dissolved in a fluid called the ‘mobile phase’, which carries it through a structure holding another material called the ‘stationary phase’. The various constituents of the mixture travel at different speeds, causing them to separate. Chromatography can separate complex mixtures with great precision. Even very similar components, such as proteins that may only vary by a single amino acid, can be separated with chromatography.
Depending on the activities of an organisation, there are a number of roles that would be involved with occupational health in the workplace, for example: 6
an occupational health physician an occupational health nurse a physiotherapist a counsellor or psychologist an occupational hygienist (Note: occupational hygiene, as discussed earlier, is a different profession involving more proactive interventions, although hygienists often work with occupational health practitioners) an ergonomist.
Health surveillance is
the on-going assessment and/or medical examination of an employee at regular intervals to determine the employees’ health state in the context of exposure to occupational health hazards
The objectives of health surveillance are to: 3
Protect the health of individual employees by detecting as early as possible adverse changes which may be caused by exposure to substances hazardous to health Help evaluate the measures taken to control exposure Collect, keep up to date and use data and information for determining and evaluating hazards to health.
Health surveillance is necessary under CoSHH Regulation 11 when: 6
An employee is exposed to one of the substances specified in Schedule 6 Is engaged in a process specified in Schedule 6 There is a reasonable likelihood that an identifiable disease or adverse health effect will result from that exposure. There is a disease or adverse health effect associated with the hazardous substance in use, for example: asthma, dermatitis, cancer. There is a reasonable likelihood that the disease or effect may occur under the particular working conditions. There are valid techniques for detecting indications of the disease or the effect.
Health surveillance requiredSystemic agents 2
Appropriate clinical or laboratory investigations Biological effect monitoring
Health surveillance requiredSubstances known to cause severe dermatitis 1
Skin inspection by a responsible person
Health surveillance requiredChrome solution, acid or compounds in: Electrolytic plating or oxidation of metal articles Dyeing processes etc. Liming and tanning of raw hides and skins1
Skin inspection by a responsible person
The benefits of health surveillance include: 4
Ensuring the early identification and treatment of an occupational disease. Provision of statistics relating to the health of the workforce. A feedback mechanism for risk assessments, to establish whether control measures are effective. Provision of evidence of due diligence and relevant information for defending legal action.
Biological monitoring measurements reflect the total uptake of a chemical by an individual by all routes. It is often used to complement….
personal air monitoring (which measures inhalation of a chemical in the air in a person’s breathing zone).
Biological monitoring may be particularly useful in circumstances where there is likely to be: 5
When there is significant absorption by non-respiratory routes, for example: significant skin absorption and/or ingestion. Where control of exposure depends on respiratory protective equipment. Where there is a reasonably well-defined relationship between biological monitoring and effect. Where it gives information on accumulated dose and target organ body burden that is related to toxicity. When there is a specified guidance value against which a comparison might be made (such as in EH40).
Practical difficulties that may be encountered during biological monitoring are that biological monitoring is normally conducted on a voluntary basis, unless required by statute, for example: lead. Consequently the informed consent of those involved would have to be obtained and their concerns overcome. Other difficulties include: 6
The availability of suitable facilities or a location to carry out the monitoring especially if this has to be done at the end of the shift. The availability of specialists to carry out the monitoring, for example: if blood samples are to be taken. Maintaining the integrity of samples to avoid cross contamination and ensuring there is no possibility of cross infection. The fact that there are few guidance values available for comparison. Exposure may be non-occupational. The cost of carrying out biological monitoring is high.
In order to achieve an effective exposure assessment it is essential that clear criteria are available for interpreting the results of biological monitoring. For this reason the HSE has established…
a system of non-statutory Biological Monitoring Guidance Values (BMGVs) to provide an authoritative guide to the interpretation of biological monitoring results. The BMGVs can be found in Table 2 (page 52) of the HSE publication: EH40/2005 Workplace exposure limits.
BMGVs are set where: 3
they are likely to be of practical value suitable monitoring methods exist there are sufficient data available.
The type of data that is available will vary between substances and therefore the route taken to deriving the BMGV will vary between substances. BMGVs are either based on: 3
A relationship between biological concentrations and health effects Between biological concentrations and exposure at the level of the WEL Are based on data collected from a representative sample of workplaces correctly applying the principles of good occupational hygiene practice.
Health guidance value (HGV) HGVs are set at a level at which, from the scientific evidence available,….
there is no indication that the substance being monitored is likely to be injurious to health.
Benchmark guidance value (BGV) BGVs are not health based. They are set at a level….
achievable by good occupational hygiene i.e. they are practicable, achievable levels set at levels achieved by 90% of a representative sample of workplaces with good occupational hygiene practices.
Health surveillance is a process. It may be a regular planned assessment of one or more aspects of a worker’s health, for example:
lung function or skin condition
There are a number of health surveillance procedures that can be used. The most suitable one will depend on the particular workplace circumstances: 4
Medical surveillance, i.e. by a registered medical practitioner, which may include clinical examinations and measurements of physiological, for example: lung function testing, which may show as changes or alterations in body function. Enquiries about symptoms, inspection or examination by, for example: an occupational health nurse. Inspection by a responsible person, such as a supervisor or manager, for example: chrome ulceration. Review of records, i.e. the occupational history of workers during and after exposure.
The main steps involved in a biological monitoring programme are: 8
Step 1: Define the purpose of the programmeStep 2: Appoint a competent person to manage the programme Step 3: Define the monitoring strategy Step 4: Consult on the programme Step 5: Discuss the programme individual employees concerned Step 6: Collect, store, transport and analyse sample Step 7: Give feedback Step 8: Act on the results and evaluate the effectiveness of the programme
A manufacturing process involves the use of three organic solvents, exposure to which is controlled by local exhaust ventilation (LEV) and personal protective equipment. The LEV system is regularly inspected and is subject to thorough examination and testing on an annual basis. (a) Outline how the exposure of the process workers to solvent vapours could be assessed. 10 marks (b) Outline how the data obtained could be used to determine if the exposure of the process workers to the solvents is adequately controlled. 10 marks
The outline could have been based around the 3 stage monitoring strategy as described in HSG173 comprising an initial appraisal and then a basic and, if required, a more detailed study. The initial appraisal would consider: the nature of the solvents involved, for example whether they were toxic, harmful or irritant the existing control measures such as the local exhaust ventilation and the personal protective equipment provided the health surveillance records the known health effects of the solvents on the body and target organs the volatility of the solvents at the process and/or workplace temperatures the synergistic or additive effects of the three solvents the frequency and duration of exposure and any WELs or relevant biological guidance values. As a result of this appraisal a decision could be taken on the necessity to undertake workplace monitoring. A number of sampling methods could be used including: static, personal, passive, active, direct reading and laboratory analysis. The equipment used would include stain and adsorbent tubes. It would also be necessary to carry out biological monitoring to measure what has actually been taken into the body rather than the airborne concentration. b.)The data would enable comparisons to be made: between actual exposures from personal sampling to the relevant WELs (workplace exposure limits) between the workplace monitoring results and in-house and industry standards between the results of biological monitoring and those of biological monitoring guidance values (BMGV). If personal monitoring exposure values were very close to the workplace exposure limit (WEL) or one or more of the solvents was a carcinogen or asthmagen, then further monitoring would have to be undertaken as advised in HSG173 to confirm whether the solvent required further control to bring its exposure to a level as low as is reasonably practicable. A comparison would also have to be made between the performance of the personal protective equipment provided against information contained in material safety data sheets (MSDS) such as, for example, the chemical resistance of gloves. Finally the results of the annual examination and testing of the local exhaust ventilation could be compared with its commissioning data and the performance recommended in HSG258 to ensure the adequacy of its level of control.
(a) Use the data below to calculate the 8-hour Time-Weighted Average (TWA) exposure to a solvent for a factory worker. Your answer should include detailed working to show your understanding of how the exposure is determined. 7 marks 08.00 – 10.30 Weighing ingredients 140 10.30 – 10.45 Break 0 10.45 – 12.45 Charging the mixers 100 12.45 – 13.45 Lunch 0 13.45 – 15.45 Cleaning equipment 25 15.45 – 16.00 Assisting maintenance staff 0 Assuming that exposure is zero during all other times.
To calculate the 8-hour time-weighted average, each time period and exposure need to be multiplied together, then added including the periods of zero exposure and the total divided by eight. TWA = (occupational exposure x exposure time) + (occupational exposure x exposure time) + … / 8 From the data provided this would result in the following calculation: (140 x 2.5) + (0 x 0.25) + (100 x 2) + (0 x 1) + (25 x 2) + (0 x 0.25) / 8 = 350 + 0 + 200 + 0 + 50 + 0 / 8 = 600 / 8 = 75 ppm Note: Remember to include the correct units with the answer. Care should be taken to reflect the period of time accurately as a fraction of an hour i.e. 15mins = 0.25 hours.
(a) Identify the circumstances when health surveillance would be considered appropriate according to Regulation 11 of the Control of Substances Hazardous to Health Regulations 2002 (COSHH). 2 marks
Circumstances where health surveillance would be considered appropriate under Regulation 11 of COSHH include: where employees are exposed to a substance and engaged in a process which are both listed in Schedule 6 of the Regulations when there is an identifiable disease or health effect associated with exposure to a hazardous substance and a reasonable likelihood that the disease will occur when there are valid techniques for detecting indications of the disease or health effect which are of low risk to the employee.
(b) Outline the arrangements and facilities that an organisation should put in place if they are to carry out health surveillance in accordance with the COSHH Regulations. 10 marks
Procedures / arrangements: carrying out of medical surveillance for Schedule 6 substances by an appointed doctor on an annual basis the completion of other health surveillance by a suitably qualified person such as an occupational health nurse or other responsible person under the supervision of a registered medical practitioner procedures for assuring the integrity of any samples taken and their submission to an accredited laboratory informing an employee if an adverse health effect or disease is identified during the surveillance the maintenance of up to date health records which should be confidential, securely kept and retained for a period of forty years arrangements for employees to view their own health records. Facilities: Allocation of a suitable room which would ensure: privacy toilet and hand washing facilities sufficient space to store records.
(c) A small engineering company uses metal working fluids which can cause dermatitis and occupational asthma. Assuming the engineering company has the necessary arrangements and facilities referred to in part (b); outline the practical steps this company could take to meet its responsibilities under Regulation 11 of COSHH. 8 marks
Practical steps that the engineering company could take include: the appointment of a responsible person to oversee health surveillance undertaking regular skin inspections of the employees and, at the same time, monitoring any breathing problems they might be experiencing referring those with breathing problems to occupational health staff for medical assessment training employees to undertake their own skin inspections and advising them to report any problems they might have with skin irritation or breathing organising and administering the completion of confidential questionnaires for skin and breathing issues introducing a record keeping system for health surveillance information carrying out a regular analysis both of this information and of sickness absence data.
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 marks (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 marks
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.)Reasons could have been divided into those to do with: working environment and the tasks being performed those resulting from possible failures with the monitoring equipment 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 misreading 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. The possibility of deliberate sabotage could not be discounted.
(a) Give the meaning of the term ‘biological monitoring’. 2 marks
Biological monitoring is concerned with the measurement or assessment of hazardous substances or their metabolites in tissues, secretions, excreta or expired air.
(b) Outline the circumstances in which biological monitoring may be appropriate. 4 marks
Biological monitoring is a complementary technique to air monitoring or sampling and can be used to determine: if existing controls are adequate when information is required on the accumulated dose in a target organ when there is a specified guidance value against which a comparison might be made (such as in EH 40) when there is significant absorption by non-respiratory routes in circumstances when there is significant reliance on personal protective equipment where required by statute such as for example the Control of Lead at Work Regulations.
(c) Outline the practical difficulties that an employer must take into account when introducing a programme of biological monitoring. 4 marks
Practical difficulties include: obtaining the informed consent of those involved and overcoming their concerns because, apart from the monitoring required by statute, biological monitoring would normally be conducted on a voluntary basis the availability of suitable facilities or a location to carry out the monitoring especially if this has to be done at the end of the shift the availability of specialists to carry out the monitoring, for example, if blood samples are to be taken maintaining the integrity of samples to avoid cross contamination and ensuring there was no possibility of cross infection the fact that there are few guidance values available for comparison that exposure may be non-occupational the cost involved in carrying out the exercise.
It is often necessary to monitor an employee’s personal exposure to hazardous substances. 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 marks(b) Outline the type of equipment AND the methodology used to determine the employee’s personal exposure to the hazardous. 14 marks
The gravimetric method for measuring personal exposure to hazardous substances may be used for measuring total inhalable or respirable dusts for instance in a woodworking workshop or in the manufacture of chemicals. Microscopy would be used for the measurement of fibres such as following the accidental disturbance or planned removal of asbestos. Chemical analysis is used in the measurement of gases, vapours and fumes in workplaces such as laboratories or those involved in the manufacture of chemicals. b.)With the gravimetric method: A filter attached to a pump is used. There are three main types of sample head depending on the type of dust being determined. These are: the multi-orifice (7 hole) sampler, the IOM inspirable dust sampler or the cyclone head. The filter is weighed before and after sampling. The concentration, expressed in mg/m³, is determined from the weight gain and the volume of air used. With microscopy: A membrane fitted on an appropriate sampling head such as a cowl is attached to a pump. After sampling is completed, a phase contrast microscope is used to count the fibres. The number of fibres in a known proportion of the sample is calculated and extrapolated to the whole sample with the result being expressed as fibres per millilitre of air (f/ml). With chemical analysis: A tube or sampling head with a filter impregnated with an adsorbing material such as charcoal, tenax or silica is attached to a pump. After sampling it is desorbed and analysed in a laboratory. The analysis techniques which can identify both the chemical and its concentration include mass spec or IR spectrometry and gas chromatography. Concentrations are expressed in parts per million or milligrams/m³. General points associated with each monitoring method include the necessity: to calibrate the pumps used to draw a known volume of air through the filter or tube to take a number of samples to minimise errors in measurement to ensure the sampling head was placed in the breathing zone to use the appropriate methods (MDHS)for determining the hazardous substances.
Methanol (an organic solvent) is being used in the production of a specialist coating. An employee’s measurement of exposure to methanol varies throughout their 8-hour working day. The results of measurement of their exposure are as follows: Measuring out and adding methanol 15 minutes 320 Adding other components to the mix 1 hour 100 Supervision of mixing and decanting 2 hours 125 Clean down of equipment using solvents 3 hours 150 Assume that exposure is zero at all other times (a) Calculate the 8-hour Time-Weighted Average (TWA) exposure to methanol for the employee. Your answer should include detailed working. 8 marks
TWA = (occupational exposure x exposure time) + (occupational exposure x exposure time) + … / 8 = (320 x 0.25) + (100 x 1) + (125 x 2) + (150 x 3) / 8 = 80 + 100 + 250 + 450 / 8 = 880 / 8 = 110 ppm Note: Remember to include the correct units with the answer. Care should be taken to reflect the period of time accurately as a fraction of an hour i.e. 15mins = 0.25 hours.
Information relating to methanol in EH40 Workplace Exposure Limits is as follows: Substance MethanolCAS Number 67-56-1 Long-term exposure limit (8-hour TWA limit reference period) 200ppm 266mg/m3Short-term exposure limit (15-minute reference period) 250ppm 333mg/m3CommentsSk R11, 23/24/25, 39/23/24/25 (b) Outline the following terms: (i) Chemical Abstract Services (CAS) number 2 marks (ii) Short-term exposure limit (15-minute reference period) 2 marks
(i) A CAS number is a unique number, recognised internationally, which is assigned to identify a particular chemical, thus avoiding confusion between chemicals with similar names. (ii) A short term exposure limit (15 minute reference period) represents the maximum permissible exposure by inhalation in a 15 minute period. This is relevant where substances may cause adverse and acute effects after a brief exposure. For substances with no assigned short term exposure limit (STEL), it is usual to apply a figure of three times the long term exposure limit (LTEL) as a guideline.
c) Using your results from part (a), the original exposure information in Table 1 and by selecting the relevant data from Table 2, explain what actions might be required by the employer in order to comply with the Control of Substances Hazardous to Health (COSHH) Regulations 2002. 8 marks
The Time Weighted Average (TWA) calculated in part (a) needed to be applied to the additional information contained in Table 2, to determine whether the employer needed to take any action to comply with the requirements of the COSHH Regulations of 2002. The conclusion should have been that the long term exposure (calculated as 110ppm) did not exceed the WEL (given as 200ppm) and it would therefore be sufficient to continue with, and monitor, the existing control measures. However, the short term exposure limit (of 250 ppm) was exceeded during the time when the employee was measuring out and adding the methanol (320 ppm) and consequently further control measures would be required for that part of the process. These might include, for example: substitution with a less hazardous substance automatic dispensing of the solvent installing local exhaust ventilation or improving its efficiency if already installed wearing respiratory protective equipment to reduce inhalation and personal protective equipment to avoid splashing to the skin since the reference to SK indicates that the substance may enter the body through the skin Measuring the level of exposure to other components and comparing them with their respective WELs, and investigating any possible synergistic or additive effects, might also be a good idea.
A manufacturing process involves the use of a solvent which has a Workplace Exposure Limit (WEL). (a) Explain what is meant by the term WEL and how it relates to the term “adequate control” as defined in the Control of Substances Hazardous to Health (COSHH) Regulations 2002. 5 marks (b) Outline a range of methods and equipment that could be used to measure the personal exposure of the process workers to this solvent. 7 marks (c) Exposure of the process workers to this solvent is controlled by local exhaust ventilation (LEV) and personal protective equipment (PPE). The LEV system is regularly inspected and is subject to thorough examination and testing on an annual basis. Using results from personal exposure measurements and information relating to the control measures in use, outline how you could determine if the process workers’ exposure to this solvent is adequately controlled.8 marks
A WEL is the maximum concentration of an airborne substance averaged over a reference period (either a short term exposure limit of 15 minutes, or a long term exposure limit of 8 hours), to which employees may be exposed by inhalation. ‘Adequate control’ is only achieved if the WEL is not exceeded and the principles of good practice are met. There are also additional requirements for carcinogens, mutagens and asthmagens. b.)Personal monitoring is used to establish the concentration of an airborne substance within the employee’s breathing zone, which is generally accepted to be no more than 30cm from the mouth. Personal monitoring sampling apparatus to measure gas or vapours in air, consist of: a sampling head with a filter impregnated with adsorbing material (charcoal or silica, for example), positioned in the wearers breathing zone, connected by tubing to a calibrated, portable flow plump. Once the monitoring (over a specified period) is complete, analysis via spectrometry, spectroscopy or chromatography will identify the chemical and its concentration. Note: Relevant MDHS documents on the HSE website (Methods for Determining Hazardous Substances) describe the methodologies for measuring exposure to solvents. You are not expected to have detailed knowledge about the name/number of these MDHS documents. c.)Comparing the results of personal exposure monitoring with the relevant Workplace Exposure Limit would help determine if the workers exposure to the solvent is adequately controlled. The results of LEV testing compared with the commissioning data for the LEV system could indicate a drop in LEV performance over time, which may result in the control of exposure deteriorating. Comparing personal exposure monitoring results to PPE or RPE specifications would also be useful in determining their effectiveness as a control measure.
