Analysis of information sources in references of the Wikipedia article "Список вибухів та пожеж на військових складах в Україні" in Ukrainian language version.
Conclusion: A massive explosion occurred on the site of the Pavlograd Chemical Plant. Not a train loaded with Ukrainian S-300's. "To date, more than 1.8 thousand tons of expired solid rocket fuel are stored on the site. It has been 20 years since its expiration date."