I don't know if you have any experience working in triage - I have none, but I googled on "triage labels" and found this on the Scottish National Health Service website:
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The standard format Casualty Triage Label may be folded and fixed to the patient to give a clear indication of the Triage category. Triage categories, shown on the label by both category number and colour coding, are:
* 1 Red: requires immediate evacuation and treatment to save life.
* 2 Yellow: requires urgent evacuation and treatment but whose life is not in jeopardy.
* 3 Green: evacuation and treatment may be delayed. This category includes the lightly injured, walking wounded and others whose condition would not be affected by delay.
* White: dead - clearly labelling the dead saves time and makes further involvement by Health Service staff unnecessary. The triage label has space for a note by the doctor pronouncing death, the time and for police information.
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Stapling white sheets of paper to the casualties' clothing would not have allowed the rescuers to take advantage of the colour coding scheme. Worse, it might have had the unwanted side effect of misleading other rescuers arriving on scene into thinking that living casualties were dead - because that is what a white label signifies.
I saw no indication in the article that the lack of pen and paper in any way impaired the responders' ability to treat the casualties. I got the impression that the triage labels were used when they became available simply to make it easier for ambulance attendants arriving to decide which casualties required priority; without them, the doctors would likely have found some other way to achieve the same result.
Whether this figured into the writer's decision-making I have no way of knowing. But to treat 15 seriously injured casualties and have them all evacuated to hospital in the middle of rush-hour (with the transportation system all but shut down) in 2 hours and 20 minutes (from the time of the explosion to the last casualty being loaded for transport) signifies to me a very high degree of professionalism and competence.
Not a criticism - you're quite right that we should always take the opportunity to ask if something could have been done better. But I think you may have been reading something into the doctor's comment that he didn't even have a pen that wasn't warranted.
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"The mind is not a vessel to be filled but a fire to be kindled."
-Plutarch