On July 30, ACGIH announced the release of its 2019 two-tier “Under Study” list, which includes chemical substances and physical agents to be considered for Threshold Limit Values and Biological Exposure Indices. Welding fume, cyclohexane, sodium silicate, and styrene oxide are among the chemicals recently added as tier 1 entries, which indicate chemical substances and physical agents for which ACGIH may issue a Notice of Intended Change or Notice of Intent to Establish in the upcoming year. NICs and NIEs represent additional steps toward the issuance of a TLV or BEI. Ionizing radiation was added to tier 1 of the physical agents Under Study list, and hyperbaric pressure was recently added as an “other issue under study.” Tier 2 entries are substances and agents for which ACGIH will not issue an NIE or NIC in 2019. Chemicals recently added to tier 2 of the Under Study list for TLVs include diacetyl, hydrogen peroxide, and isoprene. ACGIH has presented its Under Study list in two tiers since 2006. View the full list on the organization’s website. More information is available in ACGIH’s press release. TLVs and BEIs are health-based values derived from ACGIH’s conclusions of the exposure levels that typical workers can experience without adverse health effects. According to ACGIH, BEIs are guidance values for assessing biological monitoring results. Most BEIs are based on a direct correlation with the TLV, although some are instead directly related to the development of an adverse health effect. For more information, see the TLV/BEI overview on ACGIH’s website.