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NCC lowered ice thickness standard to push Rideau Canal Skateway open in February | CTV
(ottawa.ctvnews.ca)
Posting this one despite not being a resident of Ottawa. Because I'm somewhat of an ice guru, having been involved in the construction of many ice roads, runways, etc.
There is a rule of thumb in ice safety engineering called "Gold's Equation". Expressed in metric, it goes: w=4h² where h is the thickness in cm, and w is the weight it can sustain in kg.
The equation has been used safely for decades, but there are several variations on it.
(1) It assumes that your measurements are made manually, and that there is some statistical variation that are not captured by the exact locations of your measurements. If you have something that can do continuous measurements (like a GPR), you can use 7 as your factor instead of 4, as you've got better info about the thinnest spots.
(2) It assumes the ice is clear ice (also called blue ice). White ice is treated as only contributing half to thickness because it is weaker.
(3) It assumes the load isn't static. If a load is parked on the ice for 12 or more hours, you treat that load as weighing twice as much.
With all of this in mind, what usually happens is: you go measure the ice. If it passes w=4h² at the outset for your required load, you kind of just accept and move on. But if it doesn't pass, you start looking for ways to get your load approved -- hire a GPR and scan, or spray water on the surface to build more white ice faster, etc.
30cm, as per the article, will handle loads of up to 3600kg. Which is a lot, particularly when compared to skaters. But a Zamboni full of water or a snowplow or something could be risky. Bring out a GPR and truly find your thinnest spots and maybe you can get 4200kg approved. Etc.
This is likely a non-story, for those of use versed in ice safety. But it was worth my time to type it out :)