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.