Reasonable Maximum Exposure

A total of 10,000 iterations or calculations of dose were performed as part of this simulation, and Figure 4 shows the resulting distribution of average daily doses of chlorpyrifos as determined by the Monte Carlo simulation. Common practice in exposure and risk assessment is to characterize the 50th percentile as a "typical" exposure and the 95th percentile as the "reasonable maximum" exposure.4 The distributional analysis for these calculated doses... 

Reasonable maximum exposure (RME) Used in conservative exposure assessment calculations - based not on a worst-case scenario, but on 90 % and 95 % upper confidence limits on input parameters (AIHA, 2000). 

A baseline risk assessment is conducted to assess the potential human health and environmental impacts associated with soil contamination. The primary exposure pathways evaluated for explosives contaminated surface soils are dust inhalation, soil ingestion, and dermal absorption. Reasonable Maximum Exposure (RME) concentrations are based on the 95% upper confidence interval (UCI) on the arithmetic mean of soil sampling data. The land use scenarios quantitatively evaluated may include industrial and residential use, utilizing EPA standard default exposure parameters. 

Maximum exposure limit (MEL) - the maximum eoneentration of an ahhome substanee, averaged over a referenee period, to whieh employees may be exposed by inhalation under any ekeumstanee. Thus, exposure to a ehemieal assigned an MEL must be as low as is reasonably praetieable and, in any ease, below the MEL. 

In the UK a list of occupational exposure limits is published by the HSE in Guidance Note EH40, which is updated annually. There are two kinds of occupational exposure limits maximum exposure limits (MELs) and occupational exposure standards (OESs). For substances which have been assigned a MEL, the level of exposure should be reduced so far as is reasonably practicable and in any case should not exceed the MEL. For substances which have been assigned... 

Copeland (USA) 1993 Assessment of exposures at a wood treatment site by comparing Monte Carlo analysis and EPA s Reasonable Maximum Exposed Individual (RMEI) approach Soil samples of PCDDs and PCDFs mg/kg/day... 

Carcinogens are assessed by estimating the excess lifetime cancer risk and therefore always have an averaging period of 70 years (the biblical life span of three score years and 10). Exposure periods, however, represent reasonable maximum estimates of exposure to the soil at a site. 

Determine the percent of time that the potentially exposed population (s) spends in the contaminated area. For people in a commercial or industrial area, a reasonable maximum daily exposure period is likely to be eight hours. If the population is residential, a maximum daily exposure period of 24 hours is possible. We should determine if activities occur primarily indoors, outdoors, or both. Determine how activities change with the seasons. 

In the U.K., the Health and Safety Executive (HSE) publish recommended levels for occupational exposure as maximum exposure limits (MEL), which are reasonably practicable for all work activities and occupational exposure standards (OES) which cover realistic plant design, engineering and control of exposure and can be used to help in the selection of personal protective equipment. Further subdivision of limits occurs into long-term (usually 8-hour) and short-term (10-minute). Short-term limits are of use where brief exposure may cause acute effects. Both levels are expressed as time-weighted average concentrations (TWAs) over the specified period. Studies of OELs in other countries reveal that there are some differences, but generally they fall close to each other in industrial societies. ... 

In the United Kingdom, there are two types of occupational exposure limits occupational exposure standards (OESs) and maximum exposure limits (MELs). An OES is set at a level at which there is no indication of risk to health, while the MELs are set for materials for which serious health implications exist, but which due to socioeconomic factors must have a numerically higher value in order for the controls associated with certain uses to be regarded as reasonably practicable. 

In order to clarify an environmental effect it can be advantageous to analyze longer lengths of hair—3 to 5 cm—since the analysis results then reflect an average of several months. Such results are valueless for individual hair analysis since the maximum exposure can differ markedly from the mean. For the same reason it is necessary to know whether or not the hair analyzed has been sorted into the different growth cycles. The analysis results obtained with an unsorted hair sample could lead to false interpretation of the results if they were used for an individual assessment [59]. Such false interpretations are avoided by using anagen hair follicles for individual hair analyses. 

The list of exposure limits is divided into two basic parts — namely Maximum Exposure Limits (MELs) and Occupational Exposure Standards (OESs). For substances that have been given MELs, exposure should be reduced as far as reasonably practicable, and in any case should not be exceeded. With respect to OESs, it will be sufficient to ensure that the level of exposure is reduced to the OES level. This latter requirement reflects the standard demanded for compliance with the COSHH Regulations but it should not obscure the desirable aim of reducing all exposure as far as reasonably practicable. 

Atmospheric corrosion typically occurs only during a small percentage of the total exposure time, typically when the surfaces are wet fix>m precipitation, dew, fog, or when hygroscopic compounds on the surfitce absorb moisture during periods of high humidity. For this reason, atmospheric corrosion occurs slowly, and long exposure durations are usually necessary. Most tests typically involve minimum durations of 1 to 3 years, with 20 years maximum exposure not unusual. Tests of shorter duration than one year not only have so litde corrosion as to make evaluation of mass loss difficult, but also suffer from the effects of seasonal variation of corrosion rate. 

If, despite the use of other control measures, exposures still have the potential to exceed the control limits, employers must provide suitable respiratory protective equipment and make sure that it is used correctly by those carrying out the work. Employers must choose RPE which is designed to provide an adequate margin of safety. To be suitable, RPE must be matched to the job, the environment, the anticipated maximum exposure, and the wearer. It should be checked to make sure it is compatible with the personal protective equipment (PPE), particularly that any PPE which protects the head or eyes of employees does not affect the fit of the RPE. It must reduce the concentration of asbestos fibres inhaled to a concentration which is as low as is reasonably practicable, and in any case to a level which is below the control limits. 

Man-made mineral fibres irritate the skin, eyes and upper respiratory tract. A maximum exposure limit has been set based on the risk of hmg cancer because a no-adverse-effect level carmot be established with reasonable certainty. ... 

In some appHcations the high heat stabiHty of the micropowder can be utilized over a reasonably wide temperature range. A maximum service temperature is normally 260°C, provided the crystalline melting point is between 320 and 335°C. Exposure above 300°C leads to degradation and possible evolution of toxic decomposition products. 

Another reason for using higher temperatures is that for an application requiring long-term exposure a candidate plastic is often required to have an RTI value higher than the maximum application temperature. The properties tested can include mechanical strength, impact resistance, and electrical characteristics. A plastic s position in a test s RTI is based on the temperature at which it still retains 50% of its original properties. 

A maximum flexural stress of 9,500 psi is assumed for polycarbonate. This conservative stress value should account for degradation in ultraviolet stabilized polycarbonate exposed to long term solar exposure. While more research is required in this area, it is reasonable to expect at least a ten year useful life for ultraviolet stabilized polycarbonate. A Young s modulus of 345,000 psi and a Poisson s ratio of 0.38 are also assumed for polycarbonate. 

The standard set of toxicological studies can be very extensive and use many experimental animals, so it is important to make maximum use of data waivers . Clearly any studies that are impossible for technical reasons have to be omitted, but there may be a justification for data waivers on the grounds of low exposure or because the study is not scientifically necessary. 

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