When a person is hired for a job where a safety vest might be required, one of the first questions is what size the vest should be for the particular job at hand. While sometimes the purpose of a safety vest is simply to create a visible stripe so as to ensure an employee is visible during the night or in traffic, sometimes it's more important to use something like OK1 safety vests which can also protect the wearer from the elements of high heat, potential acid damage or other environmental concerns that sometimes come with highly physical jobs.