one input variable at a time while leaving others constant, to examine effect on output propagation of uncertainty examining how uncertainty in individual parameters affects the overall uncertainty of the exposure assessment probabilistic analysis varying each of the input variables over various values of their respective probability distributions(i.e. monte carlo integration) defining acceptable exposure for occupational environments simple representation of exposure risk assessment and management hierarchy based on available information occupational exposure limits are based on available toxicology and epidemiology data to protect nearly all workers over a working lifetime. exposure assessments in occupational settings are most often performed by occupational/industrial hygiene (oh/ih) professionals who gather "basic characterization" consisting of all relevant information and data related to workers, agents of concern, materials, equipment and available exposure controls. the exposure assessment is initiated by selecting the appropriate exposure limit averaging time and "decision statistic" for the agent. typically the statistic for deciding acceptable exposure is chosen to be the majority (90%, 95% or 99%) of all exposures to be below the selected occupational exposure limit. for retrospective exposure assessments performed in occupational environments, the "decision statistic" is typically a central tendency such as the arithmetic mean or geometric mean or median for each worker or group of workers. methods for performing occupational exposure assessments can be found in "a strategy for assessing and managing occupational exposures". exposure assessment is a continuous process that is updated as new information and data becomes available. systemic errors in the estimation of human exposures to environmental chemicals, the following systemic errors have been known to occur: an ever increasing number of chemicals registered for use and difficulty of regulatory agencies to keep track. many producers use the term ‘confidential business information’ to withhold information, so exposure data are per se unavailable even though under tsca, the us epa may as of 2016, review and determine if a company´s claim is valid. assessments are difficult to be kept up-to-date; underestimates of exposure occur because of inadequate assumptions about human behaviors and co-exposures ; evolving or insufficient models of toxicokinetics