Appropriate protective equipment must be worn when training weapons are used, even if just for simple drills or exercises. Fencing masks must always be worn if there is any chance that a weapon could go anywhere near a face or head. Instructors must enforce this rule.
If there are not enough fencing masks available, then change the exercise to make sure that there is no possible risk for individuals without a fencing mask (for example: by splitting the class into halves, with one half using masks and doing the drill, and the other half waiting for their turn to take the masks and do the drill; alternatively, by ensuring that there is no possible chance that the people without masks will have a weapon near the face or head, even if an accident occurs).
Standard and non-standard equipment
Typically, the advice is that modified or non-standard equipment should not be allowed. You do not necessarily know how expertly (or not) the equipment has been modified or constructed, what quality of materials have been used, and what flaws or weaknesses are present.
The use of modified and non-standard equipment may be allowed, as long as the instructor or event organiser examines it and believes that it is fit for purpose and is safe to use. Instructors have the right to refuse the use of any particular non-standard piece of equipment if it is deemed unsafe; common sense and safety should be the two deciding factors in whether or not to allow it.
Club leaders, instructors, tournament organisers, and event organisers may require certain modifications to equipment, and this might be quite a reasonable thing to do. For example, it might be a club or event requirement that blunt steel swords are fitted with some kind of external rubber, leather, or plastic tip over the point of the sword; if you believe that this (or any other similar modification) is a reasonable requirement in the interests of safety, then please do insist upon it.
Tournament organisers and event organisers may choose to specify that non-standard equipment is not suitable for the event, and may choose to specify which types of standard equipment are permissible. This decision would be to ensure that all equipment used by participants meets a minimum recognised level of performance, and so it is up to the event organisers to decide what the rules will be for any given event.
Finally, it is worth saying that equipment, whether standard or non-standard, might be sufficiently safe early in its life, but may become less safe after some amount of use. Instructors and organisers should feel able to require that equipment is in good condition, and should also feel completely able to tell participants that equipment is to be retired or otherwise forbid a piece of equipment from use at the club or event due to its current condition.
Build safety into every exercise
Drills and exercises should be constructed in such a fashion that safety is built into the activity.
Instructors should always make an explicit verbal note of safety considerations when describing the exercise, even if it seems like it should be obvious.
Levels of force and intensity
Levels of force and intensity should remain at a reasonable and acceptable level, where this is determined by the instructor and/or by the person receiving the strikes. The instructor should supervise the session to ensure that everyone is working at an appropriate level of force and intensity.
Even if speed increases in the exercise, the level of force and intensity should always remain safe.
The default assumption should be that sparring is a friendly activity, where training partners look after each other. Competition-level intensity should not be seen as the default, but instead as a special case.
Sparring in a club is a privilege and not a right. Individuals who consistently hit too hard or who exhibit unsportsmanlike behaviour should have their sparring privileges revoked until they can improve their behaviour.
Removing people from practice
At any time, the instructor may tell someone who is consistently posing a safety hazard that they should sit out or leave the practice.
This can include non-fencers; audience and any other non-participants who are present may still be capable of distracting fencers, getting in the way of fencers, or otherwise posing risks.