Boris Johnson versus the water cannon

Putting this in weird news because I thought, politics aside, the article was rather funny.


Boris Johnson versus the water cannon

London Mayor Boris Johnson has recently agreed to be hit by a water cannon as part of the ongoing row over the purchase of the weapons. But politics aside, what does the science say about how such an encounter would play out?



There is presently an ongoing political row in the UK over Boris Johnson, London Mayor, purchasing 3 crowd-control water cannons, despite parliament not having approved their use. This has developed into an ongoing controversy, with many people objecting to the use of water cannons on the public. Granted, police in Northern Ireland have been able to use water cannons for many years, but now that they could appear in London it’s a proper scandal.

As part of the ongoing row, Boris Johnson has now publicly agreed to be hit by a water cannon, to “prove the wisdom” of their purchase. This is a bold move, especially as Boris Johnson doesn’t have a great track record for making wise decisions. Many people have expressed great interest in witnessing/assisting with the encounter between Boris Johnson and a water cannon, but it may not be the spectacular slapstick that people are hoping for. Exactly how it will pan out depends on many factors.

Distance

The water cannons in question are Wasserwerfer 9000 models, with a maximum range of 65 metres throwing out 2200 litres of water a minute, or 37 litres a second, at a maximum pressure of 15 bar. That’s about 200lbs/90kg per square inch, which sounds like a lot. And it is. The average human male weighs around 194lbs/88kg, so being hit by the water canon at maximum pressure should be like several people colliding with you at once. Boris Johnson reportedly weighs 17 stone (108kg), possibly double that if he’s carrying his wallet, but a full-pressure water cannon should still be enough to knock him off his feet.

But this depends on the distance. Presumably within 65 metres the water jet maintains enough consistency and pressure to deliver a serious impact. But eventually the jet water will lose kinetic energy and disperse over a wider area, causing a two-fold reduction in the force it can deliver. So if Johnson were to stand, say, 70m from the cannon, the jet would still “hit” him per se, but at most he’d get wet and uncomfortable.

Of course, if he stands right in front of the barrel of the cannon, where the water is at its highest pressure and compressed into the smallest possible space, he risks serious or even fatal injury. Why he’d do this is anyone’s guess though. He’d need a ladder, and that’s just inconvenient.

Location

Distance from the cannon is one thing, but where this takes place is also important to consider. If a person is going to be thrown around like a dog’s chew toy by incredibly powerful jets of water, their surroundings are going to come into play very quickly. If Johnson is standing in an open field, then he may be knocked about, but there’s little else to factor in. If he’s standing next to a drop like into a river, then he could very well be pushed over the edge and into it, risking further injury. If he’s standing in front of a wall, then that could be very bad news.

All that kinetic energy has to go somewhere, and it’s usually transferred into movement of the human body. But if there’s something like a wall in the way, then for every action there is an equal but opposite reaction, to the water canon pressure will be matched by the pressure of the solid barrier. That’s a lot of pressure to apply to a squishy human form, and it may “yield” in decidedly unhealthy ways.

The water cannon are also difficult to target with great accuracy, so any bystanders there to watch the spectacle may find they’re actually involved in it.
What it's actually like to face a water cannon.

Payload

The name “water cannon” obviously suggests that they fire water, and presumably that will be the case here. But it has not been specified. Water cannons can actually fire alternative payloads, like water laced with dye or even tear gas. The former would be amusing if red dye was used, coating Johnson in the colours of the rival Labour party, whereas the latter would actually be illegal in the UK. But then, Johnson isn’t legally allowed to use water cannons at present and has gone ahead and acquired them anyway, so clearly the law isn’t a major consideration here.

There are even designs for an electrified water cannon, delivering electrically-charged fluids that “stun” targets, which is about as worrying as it sounds. Some charitable souls have even offered to donate “alternative” fluids, but given the Wasserwerfer 9000 is so named for its 9000 litre tank, this would require a group effort to fill it.

“Hit by”...?

We keep saying Johnson has agreed to be “hit by” the Water Cannon, but what he actually did was agree with interviewer Nick Ferrari that he would “stand... in front of them” when they arrive. He didn’t specify that he’d let them shoot him. “Water cannon” as a term appears to apply to the whole vehicle, and Johnson said he’d stand in front of them, so possibly he meant he’d be hit by the cannon itself, not the payload.

That’s approximately 30 tons of vehicle that’s been reinforced enough to withstand being attacked by furious mobs. Even without a full tank, it seems highly unlikely that Johnson would survive such a collision.

So until we know variables mentioned above, it’s impossible to say exactly what will happen if Boris Johnson is hit by a water cannon.

Odds are it’ll never actually happen now, meaning this article has been a total waste of time, both of mine for writing it and yours for reading it. I can only apologise for this.


Dean Burnett doesn’t actually condone the use of potentially-deadly weapons in order to make needless political points. He is on Twitter, @garwboy

http://www.theguardian.com/science/brain-flapping/2014/jun/12/boris-johnson-verses-water-cannon

I read somewhere that water cannon should only be used where people are throwing petrol bombs, no, people throwing petrol bombs should be shot with live bullets. I saw a Police man in Ireland hit by a Petrol bomb,it burned off his nose, his lips and his cheeks. After many ops he commited suicide. In a riot situation use water cannon.