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Occupational exposure limits (Application of relevant limits (OELs are…
Occupational exposure limits
Definition of occupational exposure limit (OEL)
Maximum concentration of airborne substance or mixture, referenced over a defined time period, by which employees may be exposed by inhalation
Purpose of occupational exposure limits
To allow comparison of airborne monitoring data against legal standards (Comparison Vs Legal standards)
To identify where controls need to be improved
Long-term exposure limit (LTEL) - 8 hours
Concerned with chronic health effects
Concerned with the total exposure and the pattern of exposure
Referenced over a period representing a work period, usually 8 hours
Known as a time-weighted average (TWA) worker exposure
Significance of time-weighted average (TWA)
Important to know exposure (the dose) that the worker is exposed to over a period of time (8 hours)
This will influence the amount of the substance taken into the body and the effects of that exposure
The concentration of a substance may vary over the reference period on the work activity
Exposure may exceed the limit as long as the 8-hour average does not
Short-term exposure limit (STEL) - 15 mins
Concerned with avoiding the acute health effects of exposure to chemicals
Limits the total exposure of the worker averaged over a short reference period, usually 15 mins
Where a STEL is not listed, recommendation is a figure of 3 times the LTEL
Ceiling exposure limit
The maximum allowable or acceptable concentration (MAC) that should not be exceeded
Ensures protection against acute effects, particularly those that may develop from a single exposure
Limitations of exposure limits
Other routes of entry may be cause of harm rather than inhalation
Individual susceptibility
Origin of exposure limit data (limited to exposure of individuals mainly in Europe)
Errors in monitoring - leading to misjudgement on exposure
OELs relate to single substance use (workplaces uses a number of substance)
Application of relevant limits
OELs are maximum allowable (acceptable) concentrations (MAC) of airborne substances
Measured in parts per million (ppm) for gases and in cubic metres (m3) for solids
Workplaces exposure limits (WELs) in the `UK
Where limits are exceeded, there should be a method to reduce them back under the limit values
The absence of a substance from established lists does not mean that it would not cause harm, but merely that the link has not been clearly established
Measurements should be taken regularly to demonstrate controls and compliance
Limits are the maximum and should be reduced where possible
OEL data published in EH40 (supporting to COSHH regulations)