CALGARY, Alberta — As leader of one of Canada’s largest refugee agencies, Fariborz Birjandian, a refugee himself, has years of experience welcoming the world’s most vulnerable — Kosovar Albanians fleeing ethnic cleansing, Burmese Karens evicted from Thai refugee camps and Syrians escaping the civil war.

Nothing prepared him for the Yazidis.

Recently, he entered an English-language classroom in his agency’s building near downtown Calgary, just after a 28-year-old woman had finished describing the screams of a young girl being raped by an Islamic State soldier. Suddenly, the woman fell unconscious.

Her eyes rolled into the back of their sockets, her back arched on the floor and she began to hyperventilate, her voice a rising octave until it emerged as a yelp. She grabbed fistfuls of her hair and snapped her teeth at her forearms.

“Don’t let her bite herself,” said Kheriya Khidir, an interpreter, settling down to hold one of the woman’s arms and stroke her face lovingly. Mr. Birjandian raced off to call an ambulance. Then, he slipped into a stairwell to collect his shaken emotions.