The bombings in Boston turned average citizens into first responders delivering lifesaving first aid.
Would you be able to do the same? If you're confronted by a medical emergency, officials said you should remain calm, make sure you are safe and call 911 immediately.
But there are things bystanders can do to save a life before medical personnel arrive.
"How to do compression-only CPR, knowing how to treat shock and then basic controlled bleeding," said James Boyle, a local emergency medical technician and the owner of Breath of Life CPR.
Boyle said the three lifesaving techniques can be learned in minutes.
Compression-only CPR is used when a person is unconscious and not breathing.
"Start compression by placing the heel of one hand on the chest, on the flat, bony part. The idea is to go a third to a half of their chest depth," said Boyle.
The compression, Boyle said, should be done until help arrives.
Someone in shock will be cold, clammy and will lose color. Boyle said to have them lie down and cover them with a blanket. If you can, elevate their feet.
"For bleeding, the most important thing is direct pressure," said Boyle. "If you don't have gloves then we are going to recommend to try to find a plastic bag."
A tourniquet is something you can do relatively quickly that can save a life. You want to put it above the injury. You can use a scarf or a belt. You want to tie a knot, put something like a pencil or a stick, and then all you have to do is turn it until the bleeding stops.
Learning the basics is a start, but it doesn't replace a first aid class. You can contact the American Heart Association to learn more.
Pennsylvania chapters are trying to teach 250,000 residents bystander CPR before May 26, and the American Red Cross holds first aid classes on a regular basis.
Allentown, PA 18102