. >> reporter: chrisfielder has been with the american red cross for 25 years and teaches cpr classes. he emphasizes with or without formal training. >> if it's not perfect, if you are not certified. >> reporter: people who find themselves in an emergency situation can make a difference. >> one, two, three. >> reporter: simply by learning chest compressions. >> compressions are the most important part of cpr. circulating that blood, because there is going to be some oxygen still left in those lungs, even when the person becomes unconscious. one, two, three, four, five. the clicking that you hear is a mechanism in the manequin that kelsey that -- that you are compressing the proper depth. they may crack a rib. but a cracked rib isn't life-threatening. cardiac arrest is, and that's why learning cpr is so critical. >> it's being prepared on all levels. >> reporter: because none of us can predict when we may be called upon to save a life. >> place my face shield on over the mouth. >> reporter: the rescue breath are also critical as you want to get oxygen into the lungs of someone who isn'