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の際に

at the time of

→ の
phrase Rare #39,467
at the time of A formal expression used to refer to the time of an event or occasion, often after a noun.
JA: ご利用の際には、こちらのカードをご提示ください。
EN: Please present this card when you use the service.

“爆発の際に”

in the event of an explosion

— 海の上のピアニスト (1998)