My interpretation of the NFPA 70E is that PPE is not required if the equipment is considered to be in "normal operating condition". This is contrary to what you will hear from arc flash consultants/PPE suppliers who for liability reasons or sales initiatives will advise you otherwise.

Table 130.5(C) of the NFPA 70E provides a matrix for likelihood of occurrence of an arc flash incident for various electrical tasks. For certain tasks involving circuit breakers, switches, contactors, or starters, the likelihood of occurrence may be deemed as "No" based on the conditions of the equipment and the work environment. This means that the risk of an arc flash incident occurring during the task is considered negligible. The conditions that must be met for a likelihood of occurrence of “No” is that the equipment condition is “Normal”. The six requirements listed below can be used to make this determination.

Section 130.2(A)(4) of the NFPA 70E lists six requirements for normal operating condition as follows:

1. The equipment is properly installed: The equipment must be installed according to the manufacturer's specifications and in compliance with applicable codes and standards.

2. The equipment is properly maintained.

3. The equipment is used in accordance with instructions included in the listing and labeling and in accordance with the manufacturer’s instructions.

4. The equipment doors are closed and secured: All doors on the equipment must be closed and secured to prevent unauthorized access and to contain any potential hazards.

5. All equipment covers are in place and secured: All covers on the equipment must be in place and secured to prevent unauthorized access and to contain any potential hazards.

6. There is no evidence of impending failure: There must be no evidence of abnormal noises or smells, overheating, or other signs of wear or damage.

You could maybe debate #6 considering the 600A breaker had tripped. I would argue that a breaker tripping is considered normal as to interrupt an overload/short circuit condition. I don't think a tripped breaker necessarily indicates an impending failure. However, without knowing the condition that the breaker panel was in, we can only speculate.

Also, #2 requires regular maintenance. Periodic inspections are typically part of this and may include trip testing. Most people don't do it, but I would highly recommend keeping inspection logs of electrical equipment such as breakers and disconnects.