There are numerous barriers; some more effective and safe than others. Short answer is 3 types; a mask, a non-rebreather mask, and a BVM.
The older microshield and other types without a 1-way valve should no longer be used. At least, you want a CPR mask that has a 1-way valve.
The next better would be the CPR mask with the O2 connection (and1-way valve).
As you get more into the clinical setting, a non-rebreather and BVM would be the other types.
according the red cross guidlines how many students can be in a clss for CPR
It only takes 1 person to perform CPR. An advanced CPR course can be taken to train you on 2-person CPR, which makes it easier and more productive than 1 person CPR.
Contact your local American Red Cross. If they do not have them in stock, you can order online from a business like the one on the related link.
In the world, about 1 in every 50 teens knows CPR.
You don't have to know CPR to baybsit; however, it would be a very good thing if you do know how to perform CPR. Also, many parents would prefer someone who is trained in CPR to babysit their children over someone who is not trained in CPR.
everyone
Depending on the type of class and number of students, it can range from 3 to 9 hours (CPR for Professionals) to become CPR certified.
2
Although humors, and maybe even possible, it is not suggested that you give CPR to a frog for many biohazards may exist. CPR is used for humans who require medical assistance.
CPR-FPR is CPR for the Professional Rescuer.
According to the American Heart Association, "There are no reliable national statistics on CPR because no single agency collects information about how many people get CPR, how many don't get it who need it, how many people are trained, etc.". See the related link.
9 Digit