I am a designer (mechanical engineer) who works for a fire company. My boss asked me to develop and build a new door handle and lock mechanism. Which I did successfully. It has a 16mm Solid vertical handle on the right of the door.
My boss came and viewed the work the first thing out of his mouth was "We will need a hollow handle so that it doesn't get as hot." At this point we had a discussion as to whether changing the handle from solid to hollow would change the maximum temperature.
I argued that by only changing from solid to hollow none of the heat transfer mechanisms will decrease (convection, conduction & radiation) and that only the time it takes to reach maximum temperature (or ambient) will change.
If I am wrong can you please explain why. It just seems like I have the correct answer here.
Thank you for your time.
UPDATE: 07/08/15
Not too sure if all the people who answered this will see this I hope so. Thanks for your time.
Your answers were very good and what I expected. I totally agree a solid handle stores more energy. Which when touched will be available for transfer into your hand and the longer the handle is touched the more of this energy gets transferred and the more the user gets "burned". Veritasium did a great youtube video on this.
https://www.youtube.com/watch?v=hNGJ0WHXMyE
Fun fact, in the fire standards there is no maximum temperature requirement for any part of the fire, be it being touched by the user or not.
Best Answer
Let's take the extremes as examples. Image you had an immensely dense solid door handle that has reached thermal equilibrium with the fire on the hot side of the door. The handle would have an equally immense heat capacity. If you touch that handle, then it would certainly feel very hot and burn your hand. On the other hand (no pun intended), image you had a very very thin hollow door handle, say 1 atom thin at a very low density. Again suppose it was in thermal equilibrium with the fire on the other side. Although at the same temperature as the other handle, being so thin and of low-density, it would hold very little heat energy. So if you touched it, your hand would quickly absorb and dissipate all the heat and not get burned.
So the issue is not the temperature difference of the two handles, but the extensive (total) heat capacity of the two handles. So your boss is right, a hollow handle is safer.
Another intuitive example. Which would feel colder in your hands, a super thin frozen bubble of ice, or a solid ice sphere?
Note: I feel very qualified to answer this because I have a PhD in Molecular Thermodynamics and I'm a certified fire-fighter/EMT at my local volunteer fire station.