As I’ve mentioned I’m an instructor with the National Cave Rescue Commission. During our classes we teach a variety of skills using a variety of equipment. Among the equipment we use are carabiners of various sizes and materials. The two most common materials are aluminum and steel. Each has its advantages and disadvantages.
Aluminum is almost always lighter and this can be a real advantage when you have to carry a lot of them.
An aluminum carabiner may have a MBS (mean breaking strength) of 20kN (kiloNewtons or about 4,500lbs) along its long axis. (Different designs and different manufacturers will have different values, and orientation can make a huge difference).
A steel carabiner may have an MBS of 25kN along the same axis. So, it’s obviously stronger.
But here’s the thing. When we’re moving a patient, we have to look at the entire system. In the NCRC we call this the system safety ratio (SSR). You can’t look at just one component. Imagine using a carabiner (steel or aluminum) and trying to haul a patient with dental floss. It doesn’t matter what carabiner you use, that dental floss won’t get you very far.
And honestly, if you’re at the point where the strength of the carabiner is that critical such that the difference between 20kN and 25kN is critical, I would recommend you review your entire system. There might be a better way of doing it. But yes, sometimes you MIGHT need that extra strength.
That said, why do students often reach for the steel carabiners in some cases? It’s not strength. It’s size and durability. Generally the largest carabiners we have are steel and they work best in the eyeholes of the Ferno litters we use. The Ferno has a load limit of approximately 2.6 kN. (Note how much less this is than the carabiners holding the litter! At this point 25kN vs. 20kN isn’t really important).
Besides fitting better, the steel carabiners tend to be more resistant to dings and scrapes and other forms of damage. In other words, it’s not as simple as “use the stronger one”. It’s more complex and really comes down to “use the one that best fits the situation.”
I’ve mentioned previously the use of passwords and how we have rules we often follow in regards to them. I think it’s always worth understanding the WHY of rules and when to best apply them. For some accounts, I might have an easy to remember password because if it IS breached, the harm will be negligible. For example, I’m a moderator for the sci.space.tech group on USENET (look it up if you’re below 40!). I have to log in about once a week to moderate an article. That account has a fairly simple password because in the worst case scenario, if someone DOES breach the account, the most they could do is… approve the 1 or 2 articles that come in each week. So it’s a password that’s “secure enough” (i.e. nothing anyone is going to guess from knowing me) but easy to remember.
On the other hand, the login for my E*Trade account is far more secure because if someone could access that, I could lose a lot of money.
So it’s not always “use the stronger one” it’s “use the one appropriate to the situation.”
This applies to many areas of life.