There are more than 2,000 substances used in flavoring manufacturing. The FDA regulates flavorings to ensure they are safe when eaten. Many flavorings have been in longstanding use and are classified by the FDA as "Generally Recognized as Safe" (GRAS) to eat. Thus far, the FDA does not require testing for other routes of exposure, such as inhalation.
Some flavoring manufacturers are using alternative substances for diacetyl in formulating flavorings. These compounds are acetoin and acetyl propionyl. Like diacetyl, these are 'GRAS' substances that are approved for use in food. Their chemical structures are very similar to diacetyl and have been found to be equally as harmful for inhalation.
Companies are not required to report if their flavorings contain less than 1% of diacetyl or diacetyl substitutes (https://www.dir.ca.gov/title8/5197.html).
Two companies (FA and TFA) have shown that in quantities with less than 0.5%, 1000s of ppbs have been found, yet NIOSH recommends the exposure limit (REL) for vapor inhalation up to 8-31 ppb.
CDC - NIOSH flavorings exposure
OSHA- Diacetyl and Diacetyl Substitutes
FDA New Authority on E-cigarettes
1% WITHOUT REPORTING
Department of CA Diacetyl Report of Use
Diacetyl Standard Becomes Official - Cal-OSHA
FlavourArt Clearstream
TPA Spec Sheet and Components 513-86-0
TPA Spec Sheet and Components 600-14-6
IJ - Impact of Flavor Variability
VP LIVE - interview
EUROPEAN INFORMATION
Flavor and Manufactures Association Updated List April 28, 2014
FEMA flavor - Safety/Assesment/Regulatory Flavors (E-Cigarettes)
Perfumer/Flavorist Fema
Special thanks to we2rcool =)