Does LoRa Mesh Work Underground? A Safety-Bounded Buyer Test

Prepared by the ChatField Editorial Team. Evidence reviewed August 18, 2026.

“Does LoRa work underground?” has no responsible yes-or-no answer without identifying the structure, depth, turns, materials, openings, equipment classification, power, work rules and required safety function. A signal may cross one stairwell or service level and fail at the next turn.

Current ChatField J25 is not represented as MSHA-approved, intrinsically safe, explosion-proof, a mine tracking system, an underground emergency communication system or a replacement for any required voice, alarm, check-in or rescue capability.

Short answer

Do not infer underground suitability from an open-terrain range figure. First determine whether ordinary phones and J25 terminals are permitted in the exact area. Keep all required underground communication systems in place. If a qualified site owner authorizes a non-hazardous evaluation, test only safe checkpoints and record the result as route-specific evidence.

Why underground paths are different

Rock, reinforced concrete, steel, earth, machinery, bends, doors and below-grade geometry can obstruct or redirect radio energy. Distance alone is a poor predictor. A short path through multiple walls may be harder than a longer path along a clear passage.

Open shafts, portals, ramps and aligned corridors can behave differently from rooms behind turns or sealed structures. Movement, equipment position and carrying height also matter.

Do not use the 10 km figure underground

Current J25 evidence includes 5 km in urban-obstructed testing and up to 10 km in ideal open terrain. An underground route is not ideal open terrain. Neither figure establishes a basement, tunnel, mine, subway or utility-vault result.

The J25 specifications page provides the evidence boundary. A buyer should never convert the open-terrain number into an underground guarantee.

Check equipment permission before radio performance

OSHA requires equipment in hazardous classified locations to be approved or intrinsically safe as applicable. MSHA states that manufacturers must obtain appropriate approvals for communication and tracking systems used in gassy underground mines.

An FCC ID is not a hazardous-location, intrinsic-safety or MSHA approval. Current public J25 evidence includes FCC ID 2BVP9-J25, but that does not authorize the equipment for a classified or regulated underground environment.

If the site owner cannot confirm that the exact phone, terminal and accessories are permitted, do not take them into the area.

Preserve required underground communications

OSHA 1926.800 contains specific underground-construction communication, check-in/check-out, training, independent-power and testing requirements. A product pilot cannot replace those obligations.

Keep required power-assisted voice communication, alarms, tracking, check-in procedures, emergency plans and rescue arrangements intact. J25 should not be used as the sole method for a worker to obtain emergency assistance underground.

Define a non-safety-critical evaluation

If qualified management permits a test in a non-hazardous, accessible area, define a narrow routine workflow such as a labeled test message between a surface office and a safe lower-level checkpoint. Do not conduct the test during active blasting, confined-space entry, energized work, flooding, fire, gas release or another hazardous condition.

Identify a responsible supervisor, observer, stop conditions and an approved independent communication method.

Map the path as segments

  • surface office to entrance or portal;
  • entrance to first safe checkpoint;
  • straight passage segment;
  • turn, door or change in elevation;
  • equipment or vehicle obstruction;
  • final permitted checkpoint.

Record construction materials, openings, depth, turns, machinery, door state and device position. A pass on one segment does not prove the next segment.

Test the complete J25 workflow

The smartphone is the interface. Bluetooth connects it to the carried J25 terminal. The configured terminal carries supported traffic through the local LoRa mesh to another equipped terminal and paired phone.

Both the phone and terminal must be permitted, powered and paired. The phone alone does not transmit LoRa. The terminal is not held like a conventional walkie-talkie.

Review the How It Works page before defining the safe test path.

Use participating relays only where permitted

For current planning, evaluate no more than two participating relay nodes where the tested layout and configuration permit. Do not place a relay inside a restricted, hazardous, inaccessible or unapproved area to improve coverage.

Every participating node requires an approved location, power plan, responsible owner and retrieval method. Remove one node in a controlled test and confirm the fallback.

Record pass, marginal and fail

A pass should require repeated completion of the agreed end-to-end message at the exact checkpoint. Mark delayed, reposition-dependent or inconsistent results as marginal. Record failure rather than moving into an unsafe area to chase a signal.

Retest after construction, door changes, new machinery, route changes, software updates or revised site rules.

Underground boundary checklist

  • Qualified site owner and safety authority identified
  • Exact area classification confirmed
  • Phone, J25 and accessories permitted
  • Required communications remain primary
  • Non-safety-critical test workflow
  • Independent fallback and observer
  • Safe checkpoints and stop conditions
  • Materials, turns, doors and equipment recorded
  • Phone-to-terminal pairing confirmed
  • Direct and permitted relay paths separated
  • Pass, marginal and fail criteria
  • Result limited to tested route and configuration

Contact ChatField procurement support with a non-sensitive route description, destination market and permitted operating zones. ChatField may help scope a bounded evaluation but cannot approve equipment for a hazardous or regulated underground location.

Sources reviewed

OSHA and MSHA do not endorse ChatField or J25. Their materials define safety and approval boundaries, not J25 underground performance.

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