ARIA (France) http://www.aria.developpement-durable.gouv.fr/  
Hosts the ARIA databases of industrial accidents but also contains many in-depth reports of those accidents including chemical accidents.

Dutch Safety Board  https://www.onderzoeksraad.nl/en/ 
The Dutch Safety Board investigates into the causes of disasters and accidents, including industrial disasters. 

EC-JRC Lessons Learned Bulletin https://minerva.jrc.ec.europa.eu/en/shorturl/minerva/publications
A summary of lessons learned from accidents based on a thematic topic. 

IChemE Loss Prevention Bulletin https://www.icheme.org/knowledge/loss-prevention-bulletin/free-downloads/articles/articles/
The IChemE Loss Prevention Bulletin (LPB) is a leading source of process safety case studies from 40 years of publication.  Subscription to the LPB can be ordered at: https://www.icheme.org/knowledge/loss-prevention-bulletin/subscribe/

Several articles are also available free of charge online: https://www.icheme.org/knowledge/loss-prevention-bulletin/free-downloads/articles/articles/
A few special complete issues of the LPB are also available online: https://www.icheme.org/knowledge/loss-prevention-bulletin/free-downloads/issues/issues/

United Kingdom COMAH Competent Authority  http://www.hse.gov.uk/comah/investigation-reports.htm 
The COMAH Competent Authority undertakes investigations as a result of an incident or complaint at a COMAH establishment. 

U.K.  Health and Safety Executive Safety Bulletins http://www.hse.gov.uk/safetybulletins/
The UK HSE issues safety bulletins to communicate major faults that would result in a serious or fatal injury and where immediate remedial action is required. Many of these are derived from achemical incident occurrence.

UK Health and Safety Executive accident reports https://www.icheme.org/membership/communities/special-interest-groups/safety-and-loss-prevention/resources/hse-accident-reports/
By arrangement with HSE a selection of old or out-of-print accident reports are available through the IChemE.

U.S. Chemical Safety Board  https://www.csb.gov/ 
The CSB is an independent federal agency charged with investigating industrial chemical accidents.

U.S. National Transportation Safety Board   https://www.ntsb.gov/investigations/Pages/default.aspx 
The NTSB investigations include accidents in transportations and pipelines carrying dangerous goods.

UEMS (Unplanned Explosions at Munitions Sites) database   http://www.smallarmssurvey.org/home.html
Hosts a database of unplanned explosions occurring at munitions sites, including production and storage but also a list of publications associated with munitions explosions, including accident studies, on its website.

The following organisations investigate incidents in transport and their site includes reports from investigations of accidents in transport involving dangerous substances.

Finnish Safety Investigation Authority https://www.turvallisuustutkinta.fi/en/index.html 
The Safety Investigation Authority investigates all major accidents regardless of their nature as well as all aviation, maritime and rail accidents and their incidents.

Japanese Failure Knowledge Database  http://www.sozogaku.com/fkd/en/
The Japanese Institute for the Advancement of Technology hosts the Failure Knowledge Database, a collection of case studies covering 16 industries, including the Petrochemical and the Chemical industries.  There are 100 cases presented for each industry.

Swedish Accident Investigation Authority https://www.havkom.se/en/ 
The SHK is a government authority which investigates accidents and incidents with the aim of improving safety, including accidents involving dangerous substances.

Swiss Transportation Safety Board  https://www.sust.admin.ch/en/stsb-homepage/ 
The STSB investigates accidents and dangerous incidents involving trains, aircraft, inland navigation ships, and seagoing vessels.

Transportation Safety Board of Canada http://www.tsb.gc.ca/eng/ 
The Transportation Safety Board of Canada (TSB) is an independent agency that advances transportation safety by investigating occurrences in the marine, pipeline, rail and air modes of transportation, including incidents involving dangerous goods.