Chapter 1 of NFPA 1033 is quite explicit. It applies to all fire investigators, public and private.

1.1* Scope. This standard shall identify the minimum job
performance requirements QPRs) for fire investigators.

A 1.2* Purpose. This standard shall specify the minimum JPRs
for serving as a fire investigator in both the private and public
sectors.

1.2.1 This standard shall define the fire investigator position.

1.2.2 The intent of this standard shall be to ensure that individuals
who serve as fire investigators are qualified to do so.

1.2.3 It shall not be the intent of this standard to restrict any
jurisdiction from exceeding or combining these minimum
requirements.

1.2.4 JPRs for each duty are the tasks personnel shall be able
to perform to successfully carry out that duty.
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1.2.5 Fire investigators who perform or support fire investigations
shall remain current with the general knowledge, skills,
andJPRs.

1.2.6 Fire investigators who perform or support fire investigations
shall remain current with practices and applicable standards.