Difference between Volenti Non-Fit Injuria and Contributory negligence

Greetings Tutor, I hope you are doing well.
Although i have a general idea as to the Meaning, Case Laws and Difference between Volenti Non-Fit Injuria and Contributory negligence, and it is quite easy to answer in a particular scenario if only one of them shows up as a possible option for defence used by the Defendant.

However, i often get confused when both of them comes as an Option for Defence that can be used by the Defendant.

Ex- 1) Bee injured her eye after failing to close a safety gate on a machine as instructed. She was also not wearing mandatory safety goggles as required by her contract of employment. Which of the following is this an example of?
a) Volenti Non-Fit Injuria.
b) Novus Actus Interveniens
c) Res ipsa loquitur
d) Contributory negligence
Ans – Option A

2) Bizzy Ltd operates a Building Construction Business. During the Course of a new building development some scaffolding collapses and a number of employees are injured. Their injuries would have been greater if a warning shouted by the works foreman had not enabled them to start moving away from the building.
However, two employees, Dennis and Sam, received more serious injuries. Dennis is deaf and did not hear the warning and Sam, contrary to instructions, was not wearing a safety helmet.

Which defence can may reduce the liability of Bizzy Ltd for a claim of negligence by Sam.
a) Volenti non fit injuria
b) Res Ipsa loquitur
c) Novus Actus Interveniens.
d) Contributory Negligence
Ans – Option A

One Principle that i apply in such question is to first check whether there is any Negligence on the Part of Defendant and then Negligence on the Part of Claimant if it is the Case then i select Contributory Negligence or else the Option of Volenti.

But sometimes this trick does not work, as it felt the right answer of Bizzy Ltd shall be Contributory but which was not the Case.

So can you please tell in such Scenario how to differentiate between Volenti Non Fit-Injuria and Contributory Negligence and identify which defence the Defendant would actually use?