The STM Explained Why Wind Smacks You In The Face When You Enter A Montreal Metro Station

Montreal pro tip: don't do your hair until after you're off the metro. Montrealers know the struggle of using all their body weight to force open their metro station's doors only to get smacked in the face by a blinding gust of wind that smells like the city's stale, dusty bowels.

So why does entering an STM metro station feel like an amusement park ride? The transit company took to Instagram to share the answer in an eye-opening explainer video on its ventilation system and methods.

The wind, the STM says, is due to what's called "the piston effect."

"In the public areas of metro stations, there's no ventilation system in the buildings, themselves," STM engineer Annie Mcken explains in the video.

"Instead, the circulation of the trains ensures more-than-adequate ventilation and sufficient air change in the stations."

When trains move through stations, Mcken continues, they displace air, which then pushes its way outside or in — this is the piston effect.

This, plus what the STM says are more than 150 ventilation shafts and 90 mechanical ventilation stations, are enough for the network, Mcken concludes.

The piston effect in the Montreal metro is, of course, well-documented and has been widely reported.

It also explains why the STM has those unique "butterfly" doors.

In an online document, the company says the famous doors on a fixed central axis facilitate airflow in and out of stations, reducing resistance and making it easier for riders to enter or exit.

The STM's Instagram video on ventilation also explains how metro trains, buses and adapted transport vehicles are designed to refresh the air.

This article's cover image was used for illustrative purposes only.