Smoke tablets and the use of smoke itself in drain testing is something that’s been around for over a century and is actually the first way the Victorians used to test their drainage.
Essentially once a waste system has been installed, you should be able to blow smoke inside it and there should be nowhere for the smoke to emerge – the integrity of the waste system should safely contain it within
The pipe joints should be able to keep the smoke within the pipework and the pipe ends/connections should all have water seals (or ‘traps’) to also contain it (but critically also allow waste to flow through)
Only exception would be a vent deliberately incorporated (back in the day) to allow air to enter the waste system and aid flow – however modern systems now have one-way valves (or Durgo’s or AAV’s – Aid Admittance Valves) for these
The Victorians would lightly pressurise the pipework with smoke and bellows following the pipework’s installation and if there were any issues, the smoke would escape giving a visual cue (and an odour) as to where the problem was
Nice simple, low cost system!
If smoke gets out of a section of pipework then sewage gases will as well causing malodours and possibly hazardous gas emissions (lots of nasty gases are found in sewers such as methane, hydrogen sulfide, ammonia etc. – kill you all day long in the right quantities)
The Victorians in particular showed great concern for sewer gases for another reason though as they believed it was these that spread cholera – their great pioneering of the ‘waste system’ was actually prompted by this desperate need to stop cholera killing everyone’s kids & grandparents
They were slightly off with this conclusion re the gases but the sewer systems they built still met the objective as ultimately they stopped populations drinking their own sewage (which was the real cause of the cholera epidemics – bacterial transmission)
They worked out that smoke testing pipework was better than your eyes as it relied on physics rather than human interpretation – if there was a hole or gap somewhere then pressurised smoke will always find it in a way that a casual glance doesn’t always
Same thing applies to the rat game – holes in pipes let rats out just like they do gases
You can have the best, most expensive CCTV equipment available but it is still totally reliant on the human operating it to spot the holes and anyone that has operated a drain camera will agree when I say that this isn’t easy – pipe runs are pitch black and generally smeared with grease, scale, roots and you name it
The other challenge is that decent CCTV cameras (i.e. pan & tilt units) are around 75mm in diameter so they can’t fit up all bits of any given waste system – also blind connections are a challenge as any camera has to be pushed along by a rod and therefore has challenges ‘turning corners’
Smoke gets around all of these issues…
(1) Relies on failsafe physics not a human
(2) Can get into 100% of any waste system
(3) Finds all holes in all locations and gives both a visual and odorous cue
Smoke testing is relatively out of fashion these days but is typically done with smoke tablets when undertaken – these are lit with a naked flame and then dropped into a pipe run whereupon they spit out large volumes of orange smoke until they burn out
Problem is like most combustion processes, you don’t have much control over them – great feature for arson objectives but less helpful for delicate testing scenarios
There is no off-switch for the tablets once they are underway or no way to dial them down so end result is usually smoking out an entire house which will then stink for hours until it finally all goes – not a great customer experience!
We have also learnt that customers cats casually up and leave the building when this happens but then never come back!
Pestology uses smoke tests as part of their survey analysis because they recognise the critical advantages they still offer to supplement visual CCTV work – as outlined above they will give you info that CCTV simply won’t
However here in the 21st century, Pestology surveyors use the ROM e-STEAM ‘smoke’ testing units
These machines use a water vapour form of smoke (type of vape in essence) which is much safer and cleaner than real smoke but the best advantage is its fully controllable in terms of how much volume and how much pressure – just twiddle some knobs like you do on a car stereo for some ‘base and treble’ and you can completely control the ‘smoke’ discharge that comes out the end of the delivery hose
If you do a Google and watch some YouTube, you will see just how versatile and impressive these ROM e-STEAM units are
Not only can they be used for drainage tests but in the rat game they can also be used to link burrow holes with building fabrics and other such reverse usage