Compassion is a response to the suffering of others that motivates a desire to help.
Many who see a colleague with a heavy load (metaphorically or otherwise) will feel inclined to offer support. However, this may feel like “butting in”.
Speaking legalistically, your duty to colleagues is simple: any hazard to safety and health (including mental health) needs to be reported – be it by you or by them (https://bit.ly/2SRO9DX). However, you might also like to have an open-ended discussion. This discussion should be based on compassion rather than finger-waggling and “tut-tutting”. After all, there is almost certainly a ‘root cause’ here that needs to be drawn out. Remember “things may not always be as they seem”. We are good at hiding issues like fatigue, mismanagement, and misunderstood priorities.
Compassion helps us get beyond excuses and/or defensive or superficial responses, whilst building relationships. Experience from the healthcare sector suggests this can be mutually beneficial (see http://goo.gl/Lskj4p). The subsequent hazard report will almost certainly be more grounded and useful as well.