Breaking Down Ice on a Frozen Lake – Swiss Cheese Model Analysis
During the winter of 2020 – 2021 in Hervanta, I teamed up with a group of people every Sunday to build snow structures such as igloos, duck sculptures, snow lanterns, and forts. Since the snow was dry, we used to collect water from the lake and mix it with the snow to make it wet.
This ensured that the snow would bind together (like cement) and thus, we could make big bricks of snow which solidified into ice. Despite freezing temperatures, a part of the lake used to be heated for the ducks to swim around. We used to collect the water from that part of the lake.
However, on one occasion, the lake froze completely. We did not want to go home so we decided to dig through the frozen layer of ice to access the water. We decided to dig through the ice layer using a knife, at a portion on the lake where the ice would be the thinnest. At the same time, the knife was the wrong tool to do the digging, so we asked a friend, who was arriving later, to get a hammer along with him.
After around 15 minutes of digging, we finally reached the surface of the water. But the hole was as small as a human fist. We needed the hole to be at least as big as a bucket to scoop out water.
Fortunately, the guy with the hammer arrived just a few moments later. Initially, he started hammering the ice layer, slowly chipping it off, which was much faster than the knife. However, we still needed a bucket sized hole and the hole was expanding very slowly.
Thus, I took inspiration from my carpentry ancestry and started hammering the knife into the ice like a chisel (around 5 to 6 mm away from the periphery of the hole). This sped up the process significantly. After a few moments, the hole was becoming bigger at a faster rate, but my friend wanted it to go faster. So, he directed me to hammer the knife around 10 mm away from the outer diameter of the hole.
Once I hammered the knife till its butt, he would pull away a layer of ice, by pulling the knife in the direction of the hole, like a wedge. The flat face of the knife was in the same plane as the vertical surface of the hole. The hammering effect cracked the ice around the knife, which made it easier to wedge off chunks of ice.
My friend became ambitious and asked me to hammer the knife around 15 mm away from the outer diameter of the hole. When my friend tried to wedge and pull the knife this time, it snapped into two, with the blade getting stuck in the ice and the butt in his hand.
So, what went wrong with our method? I can roughly break it down into the Swiss Cheese Model. Firstly, we communicated using an online messaging app.
I had walked past the lake about 4 days prior to our snow building endeavour and had noticed the frozen lake. I put in a message in the group that the lake was completely frozen and that we may not be able to build the next time. So, if we consider the organisation level, they knew about a possible problem with the snow building activity.
But important to consider is the latent conditions. The temperature on the day that I witnessed the completely frozen lake was -17°C. The temperature prediction on the day of snow building was -4°C. Further, the part of the lake which had never frozen before, was heated by a heating coil under the water.
So, the organisation (group) assumed that -17°C was an exceptional circumstance and that the coil would do its work at -4°C. Thus, the first layer of the Swiss Cheese Model was breached. Nobody checked the status of the lake on the day of snow building.
Now, 2 of us (me included) were the first to arrive at the building location on Sunday. We noticed the frozen lake and tried several methods to break through the ice. All failed until my friend started digging through the ice with a knife.
At this point, we figured out that the ice breaks and I understood the nature of ice (brittle) due to my background in material sciences. So, I told my friend to get a hammer along with him. I could be considered as the person in a supervisory role in this situation. I presumed straight away that my friend did not have an ice drill or that he knew which size of hammer I had in my mind.
When he arrived, I noticed that the hammer was very small, and I asked him if he had a bigger hammer. He said that he brought a small hammer because he thought that we needed it to chip some ice sculptures. Here, my miscommunication and trust in my friend led to the second failure wherein the instructions were not clearly defined.
As mentioned earlier, the temperature was indeed -4°C. That, combined with all the splashing of the water onto our clothes while hammering the knife, made it very uncomfortable to sit on the ice and dig the hole patiently. Thus, we tried to speed up the hole making process. At the same time, I knew that using the knife to pull/wedge out the ice would damage the knife, either by bending it or by breaking it. But my friend has many knives, so I presumed that he knew about the strength of the knife.
When the knife snapped into two, he remarked that he never thought that ice could break the knife because the seller of the knife mentioned that it was carbon steel. I, on the other hand, knew that this was possible. It’s all about leverage and the properties of the metal. Adding more carbon to steel makes it harder but even more brittle at the same time. Ideally, steel will show some deformation before breaking.
But since it was a carbon steel knife, it was brittle and snapped without much indication.
Thus, this led to an active failure where the knife simply snapped into two pieces. It was only a week later, that we realised that the heating coil was broken because the people who visited the lake kept feeding the ducks. The food got stuck up with the heating system and damaged it. Thus, there was a latent failure too, which was completely unforeseen by us.
Overall, the failures/errors could have been avoided through proper communication and more careful analysis of the situation. I was aware that the knife could break, but I did not say anything because I trusted my friend. I was not explicit in telling my friend the purpose for the hammer and thus, he brought a smaller hammer.
The group presumed the conditions of the lake due to an error in judgement. However, the breaking of the heating coil could not be foreseen by us and was completely out of our control. Subsequently, the city of Tampere has put in signboards that inform people not to feed the birds or animals.
Tyrone Machado Doctoral Researcher, MORE-ITN