WDR: the purpose of this story is not to judge but to draw all possible lessons and bring a conclusion and advice to avoid this kind of event from happening again. For this we suggest you to answer the following questions and to motivate your answer.
During one month the discussion will remain open for new posts and then will be closed.

1 / Is it normal to dive with a defective gauge when you know it?
2 / Who makes the mistake of diving despite this problem?
3 / Why the teacher does not understand the person? How it could have been avoided?
4 / Did the teacher had the proper behavior?
5 / Did the person had the right reaction? How would you have done in his place?

Conclusions and advices:

Thank you to all of you for your valuable comments. It seems we all agree without any doubt about the following rules:

Mistakes done:

- Divers is responsible for its own equipment and even in doubt should report the problem to the dive guide.

- Diver should not dive with defective gauge even though it apparently worked for the second dive.

- Dive center didn’t check properly the equipment.

- Diver should ask to review signs with the guide.

- Guide didn’t ask if the pre-dive check was done and if equipment was ok.

- Guide didn’t review signs.

- Guide didn’t detect that student was in trouble underwater.

- Guide and student were too far from each other.

How to prevent it:

1.It is NOT normal to dive with a defective gauge. All your gauges must be tested prior to diving. In case of doubt ask for changing it.

2. The pre-dive safety check done properly doesn’t allow diving with defective gauge. So follow the basic rules from the safety check.

3. Dive centre/instructor should test properly such item and remove faulty equipment for maintenance.

4. Both guide and student should revise signs prior to diving. It is a basic rule of safety!

5. Guide should always be alerted on a potential problem and not being too relax. Probably an incident training should be organized by agencies on regular basis. 

In terms of decision:

Student did well when she took the alternate air-source from the guide. However we think that with the distance between her and the guide (and the uncertainty of the next moves from the guide) plus the fact that she was at 12m, the safest way would be to go back to the surface at normal speed (18m/mn).

Alternate air source is the best choice if the distance between the two buddies is short (say around 2m) or if you don’t feel comfortable to go back to the surface beyond 18m (means you must have enough air to blow for 1mn).