Final answer:
The first action after arriving at a scene where CPR is being performed should be to assess the scene for safety, check the man's responsiveness, and ensure emergency services are contacted. Then, if trained, assist with or continue high-quality CPR.
Step-by-step explanation:
You arrive at the scene shortly after a 55-year-old man collapsed. Two bystanders are performing CPR. Your FIRST action should be to assess the scene for safety, ensuring that it is safe to approach the victim. If the situation is safe, you should then check the man's responsiveness. If he is unresponsive, immediately call for emergency services if it has not already been done and then continue with the CPR, making sure to perform high-quality chest compressions as described in standard CPR guidelines.
In scenarios involving CPR, always remember that personal safety comes first. Observing the scene for potential dangers like traffic, fire, or electrical hazards is crucial. If you are trained in CPR, you may assist the bystanders or take over if necessary, ensuring proper hand placement on the sternum for effective chest compressions between the lines at T4 and T9 and following the compression depth and rate as recommended in CPR standards.