I remember when I worked in the Wales and West Control, spending a night down at Canton to see what went on. Believe me, your lungs took a pounding come 0300/0400 when all the sets were being started up and prepped for service.
The person who uploaded the video actually replied to someone in the comments section about starting it up outside. They said it was because the locals likely would have seen the smoke rising and try to call the Fire Service. That 37 does look glorious though
TBH, the bulk of those billowing clouds is probably water vapor, the result of hot exhaust hitting cold, damp air. Not even an old EE V-anchor produced THAT much smoke!
