Past Perfect Continuous – When do we use it?

1. We use the past perfect continuous to describe an action that started in the past and continued up until another action in the past.

•         The house had been burning for half an hour before the firefighters arrived.
•         They had been discussing the problem for three hours before they finally came to a decision.

2. We also use the past perfect continuous for an action finished in the past whose result was visible in the past.

•         It had been snowing all night. (we could see the result)
•         He had been working all night and was exhausted.