With engine running as part of the job, my staff and I use hearing protection whenever we run one. We use ones that give about 30 dB of attenuation. I've found that using hearing protection becomes a habit. I can't mow the lawn without a set of earmuffs, and use musician's earplugs when I play drums in a local band. Use a grinder? Muffs. Use my bandsaw? Muffs. Once you've begun to notice how loud some things are, you wind up wondering what you did before you started wearing the muffs.