It's always dangerous when you turn left in an intersection. You have to cross over opposing lanes of traffic which leaves you vulnerable in a crash. It also exposes you to drivers who would never think that they might have to yield and let you turn left.
The rule in B.C. for turning left at an intersection requires that you yield to any opposing traffic in or approaching the intersection so closely that it would be a hazard. Having yielded as required, opposing traffic must now yield to you and allow you to make your left turn.
Never, ever expect the opposing drivers to follow this rule, even if you are at an intersection controlled by traffic lights that have turned yellow. In fact, this may be one of the more dangerous times to try and turn. Drivers wanting to get through before the red may not be watching for you.
It would be far safer to wait for the lights to turn red and all the opposing traffic to stop and then make your turn. In this situation you have right of way over cross traffic facing the green light to do so. It also assumes that you have properly entered the intersection on the green light to prepare for the turn.