Like-for-Like Swap in a Division 1 Area
You are an instrument technician at a products terminal. The area around the transfer pumps is classified Class I, Division 1, Group D on the site area classification drawing. A 2-wire, 4-20 mA pressure transmitter on the discharge header has failed and must be replaced. The only spare on the shelf is marked: Nonincendive - Class I, Division 2, Groups A-D, T4; 24 VDC nominal. The existing rigid conduit enters the transmitter enclosure through a listed seal fitting located 24 in. from the enclosure, and the run continues 40 ft to a junction box in the unclassified area. The line cannot be drained for another 8 hours. The shift supervisor says, It is a like-for-like swap, just do it, no permit needed.
1. Evaluate the spare transmitter against the area classification. Can it be installed? Justify your answer from the nameplate markings and the code logic.
Read the worked answer
No. The spare cannot go in.
Nonincendive protection is recognized only for Class I, Division 2. It works by limiting the energy that can appear at the instrument during normal operation; it does not survive the fault conditions that a Division 1 classification assumes can exist. The nameplate says Division 2, so that is the only environment where it is listed.
A Division 1 location requires one of:
- an intrinsically safe circuit - an IS-rated transmitter plus a listed associated apparatus (barrier or galvanic isolator) in the unclassified area, with entity parameters matched, or
- an explosionproof or purged housing suitable for Class I, Division 1, Group D.
Either path still requires verifying the T4 rating against the process autoignition temperature and confirming Group D covers the gas present.
Since the spare satisfies neither path, the correct judgement is to hold the job until the correct device arrives. The phrase like-for-like assumes the failed unit and the spare are interchangeable; the nameplates prove they are not. Installing it would put a Division 2 device in a Division 1 boundary and create an ignition source.
2. The seal fitting is 24 in. from the enclosure. Evaluate this and state what you do about it during this job.
Read the worked answer
It is noncompliant, and it matters here.
For a Division 1 conduit entry, the code requires a sealing fitting within 18 in. of the enclosure. At 24 in. the seal does not do its job: it exists to stop gas from migrating down the conduit run into the junction box in the unclassified area.
Because this job opens the enclosure and breaks the process connection, this is the moment to correct it:
- Install a listed sealing fitting within 18 in., compound poured per the manufacturer's instructions, conduit made up wrench-tight.
- If the correction cannot be made in this window, do not return the transmitter to service. Document the deficiency, raise it through the work order/MOC system, and schedule the repair.
Do not install a second seal further down the run and assume it compensates, and do not accept close enough. A seal in the wrong place is a documented safety defect, not paperwork.
3. List the permits, isolations, and safeguards required before you break the process connection.
Read the worked answer
Before any wrench touches the fitting:
- Safe work / cold work permit signed by the area authority, plus a JSA covering the specific task.
- MOC or approved deviation for substituting the instrument, since the spare is not equivalent.
- LOTO on the transfer pump motor and any isolation valves; verify zero energy by attempting a start and by test-before-touch on the conductors.
- Depressurize, drain and vent the impulse line; confirm 0 psig at the transmitter block with a gauge you trust.
- Gas test for LEL and H2S if the stream is sour; continuous monitoring if the permit requires it.
- PPE appropriate to the hazard (FR clothing, face shield, gloves), plus a fire extinguisher staged nearby.
- If re-making the conduit seal requires hot work, a separate hot work permit and fire watch.
- Barricade the area below the work and confirm the drain/vent route is safe before opening anything.
If any of these cannot be obtained, the job does not start.