Reference period

OES, OCCUPATIONAL EXPOSURE STANDARD (uk) The Concentration of an airborne substance (averaged over a reference period) at which, according to current knowledge, there is no evidence that it is likely to be injurious to employees if they are exposed by inhalation, day after day. (Specified by HSC in Guidance Note EH40.)... 

The long-term OES is 50 ppm (8 hr TWA), set to protect against CNS effects, which will also protect against liver or kidney damage and initation. The short-term OES is 1000 ppm (15 minute reference period) to minimize exposures at initant levels. 

The Occupational Exposure Standards imposed for trichloroethylene are Maximum Exposure Limits of 100 ppm (8 hr TWA) and 150 ppm (15 minute reference period). A skin notation Sk is applicable because of the potential for skin absorption. Because of its volatility, trichloroethylene is not recommended for cold cleaning it is normally used in partially enclosed vapour degreasing equipment provided with local exhaust ventilation. 

Maximum exposure limit (MEL) The maximum concentration of an airborne substance, averaged out over a reference period to which employees may be exposed by inhalation. 

Occupational exposure standards (OES) U.K, standards relating to the concentration of an airborne substance that can be tolerated without harmful effects on workers over a reference period. See Long term exposure limit (LTEL) and Short term exposure limit (STEL),... 

Reference period A specified time period allowed for human exposure to a specific concentration of a biological agent or chemical. 

Maximum exposure limit (MEL) — the maximum concentration of an airborne substance, averaged over a reference period, to which employees may be exposed by inhalation under any circumstance. Thus, exposure to a chemical assigned an MEL must be as low as is reasonably practicable and, in any case, below the MEL. 

In accordance with EEC ordinance no. 793/93 (existing substances ordinance) dated 1993, manufacturers and importers have to submit the available data for every substance listed in EINECS to the European Chemicals Bureau (ECB), if their production volume or import volume was in excess of 10 t/a in a predefined reference period. All in all, the industry has submitted data covering the basic data set of European chemicals legislation in only 14% of cases for high-volume existing substances (2500 substances > 1000 t/a) . Details concerning exposure were even more patchy. 

The retreat of glaciers will be the most obvious change in the Alps as a result of climate change. Model calculations of the expected glacier retreat in relation to the reference period 1971-1990 are shown in Fig. 3a. They were calculated for a warming in summer between +1 and +5°C and a change in annual rainfall between -20% and +30%. 

The maximum ultrasonic amplitude must be chosen so that the average threshold amplitude occurs at roughly three-quarters of the reference period. 

However, several assumptions are inherent in this interpretation of the data. First, it is assumed that the change in the observed effect (such as conversion of 850°F+, percentage denitrogenation, etc.) is linear with respect to time. Thus a linear delta-effect per period of time could be established and intermediate data could be adjusted to a MfreshM activity corresponding to that observed at the reference period and at any desired temperature. Second, it is assumed that the intermediate process parameter variations had no adverse effect on the catalyst deactivation function. For example, operation at constant temperature for a given interval of time would produce the same catalyst deactivation as varying temperatures (within limits) over the same interval of time. 

Such changes could only take place for the next reference period, starting in 2008, following the procedure laid down in the Directive. 

This issue might be more problematic, were the Commission, the Regulatory Committee and/or the Council to take the view that it would not be possible to make the appropriate amendments to Annex III without this undermining the system and provisions of the main text of the Directive -and the main text could only be amended by legislation, adopted jointly by the European Parliament and the Council, after a process that could well be too lengthy to effect the required changes before the commencement of the next reference period. 

A. Reference period consisted of 3 days prior to treatment. Measured consumption values were used as a reference for comparison purposes. 

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