Entry must be justified
NOM-033-STPS-2015, listed as current in the official catalogue, applies to confined space work in Mexico. It states that entry should preferably be avoided and the activity performed from outside where possible. The first decision is whether a person needs to enter, rather than which respirator to select.
The confined spaces entry explains the general hazard. The standard requires identification, classification and assessment of each task. Its scope includes qualifications concerning diving and underground mines that need checking where those activities are involved.
Classification and task analysis are different
Prior sampling supports classification as Type I or Type II using oxygen, flammability and toxicity criteria. Initial classification does not replace task analysis or establish that conditions will remain stable throughout the work.
The standard requires consideration of a Type I space becoming Type II because of activities undertaken. Introducing a substance, generating fumes or changing connections may create hazards absent during the first measurement. Mechanical, electrical, biological, thermal and engulfment or entrapment hazards must also be considered.
Plan, authorisation and attendance
Procedures, a specific work plan and written authorisations are needed, with a responsible person and at least one attendant. Communication, equipment, lighting, protection and nearby activities must be controlled. Records cover authorised personnel, entry, exit, time inside and sampling or monitoring results.
The permit is not a form to reuse without checking conditions. Changes to equipment, substances or the space, incidents and unforeseen hazards require review of the analysis. Coordination includes contractors and operations capable of affecting conditions from outside the space.
Prepared rescue rather than improvisation
The emergency and rescue plan must address injured workers and the resources needed to recover them. Preparation must exist before entry and match the space and task. Willingness to help does not replace training, equipment or an organised response.
This entry does not provide an entry sequence or declare an atmosphere safe from an isolated reading. Authorisation requires competent assessment, complete controls and a practical ability to respond when conditions change. The arrangement must remain valid throughout the work, not merely at the moment a permit is signed.
