Everyone who works on location should be familiar with basic first aid. Most employers will send staff on first aid courses at their request, and for freelancers it's worth checking if courses and/or funding are available via professional bodies (see Appendix A).
High sound levels
One hazard which can be cumulative is exposure to excess levels of sound, especially whilst wearing headphones and working in noisy environments. It is all too easy to overlook, but could well lead to a diminution of your hearing sensitivity if allowed to develop. Check the level you're feeding to your headphones, and whether the volume control is always set to maximum. If in doubt, ask a colleague if they think your monitoring level is excessive, ...