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The first reaction should not be an abrupt steering movement.
Check the mirrors.
Observe nearby vehicles.
Look for cyclists, pedestrians and traffic approaching from other directions.
Signal appropriately if a lane change is necessary.
Then make room when it can be done safely.
Predictable driving gives everyone around you more time to understand what is happening.
That includes the responder.
A few seconds of calm awareness can be more helpful than a dramatic maneuver.
Not Every Green Light Means the Same Thing Everywhere
This is perhaps the most important part of the subject.
Green warning lights do not have one worldwide meaning.
Vehicle-lighting laws vary between jurisdictions.
A driver who learned what a flashing green light means in Ontario should not assume the identical rule exists in another Canadian province, a U.S. state or another country.
Different authorities can reserve colors for different categories of vehicles or services.
Some uses may require authorization.
Others may be prohibited entirely.
That is why explanations online should include the jurisdiction instead of presenting one local rule as a universal fact.
The color alone does not tell the whole story.
Ontario Also Restricts Who May Use the Light
Ontario law does more than describe who can use a flashing green light.
It also restricts its operation to authorized categories.
The Highway Traffic Act identifies firefighters proceeding to a fire or another emergency.
Ontario regulations additionally identify specific volunteer medical responders who may use flashing green lights under defined circumstances.
Those circumstances are not unlimited.
For example, the regulation covers specified medical responders while responding to certain medical emergency calls, transporting a patient at the request of a government or government agency, or performing duties assigned through a municipal emergency plan.