How Are Thermal Hotspots Detected on Cargo Decks?
The detection problem on a cargo deck is not measurement — IR sensors are commodity. It is deciding which delta in which cell at which time is real.
Asking how thermal hotspots are detected is really asking three questions in sequence: how is temperature measured, how is anomaly distinguished from noise, and how is anomaly distinguished from a real thermal event. The first is solved engineering. The other two are where products differ.
Three families of measurement
Ceiling-mounted spot sensors
The legacy approach: a few dozen IR or smoke detectors on the deckhead, sampling a deck-wide volume. Trip on absolute threshold. Cheap, certified, and almost useless against the per-vehicle anomalies that matter on EV-mixed cargo.
Line-of-sight thermal cameras
A small number of high-resolution thermal imagers covering long view paths down a deck. Excellent angular resolution where the line of sight is clear; blind everywhere it is not. On a cargo deck this is most places.
Distributed sensor cell arrays
Many small IR sensor cells distributed across the overhead at vehicle-pitch density. Each cell has a narrow field of view scoped to one or two vehicles. Coverage is per-vehicle by design.
Anomaly versus noise
Once the measurement architecture is chosen, the algorithm question is the same: what crosses the threshold? A static temperature trip is the simplest possible decision rule and the worst-performing one. Engine bays cool unevenly. Solar gain through deck openings adds 10–15 °C on coastal sailings. Ambient varies 30 °C across a single voyage.
The approach we use is a per-cell rolling baseline (EWMA over recent samples) and trip on sustained delta-from-baseline rather than absolute temperature. The threshold becomes a relative quantity, robust to ambient drift.
Anomaly versus real event
A true delta in a single cell is still not enough. The most common nuisance source is solar gain on a sun-exposed cell — and it is shared by neighbouring cells. We add a coherence check: if the neighbouring cells share the delta, suppress; if the delta is local to one cell, escalate.
Latency budget
What this implies for system design
- Per-vehicle field of view, not per-deck volume.
- Relative thresholds, not absolute.
- Multi-cell coherence as the suppression layer, not as the detection layer.
- Deterministic latency end-to-end so the confirmation window is bounded.
Sources
- IMO — SOLAS Chapter II-2 and the FSS Code Chapter 9 (fixed fire detection and alarm systems): the regulatory baseline for ceiling-mounted deck detection.
- IMO MSC.1/Circ.1638 — interim guidelines for minimising the incidence and consequences of fires in ro-ro spaces, including electric-vehicle considerations.
- DNV — class guidance and research on fire detection for car carriers and ro-ro vessels.
- [VERIFY: per-cell EWMA-baseline lead-time figures (18–25 min vs ceiling smoke) are RoRoSafe bench-rig data, not externally published.]
Continue the thread
What Causes EV Fires in RoRo Ships?
The headline answer is "lithium-ion batteries." The operational answer is more useful — five compounding factors that turn an unremarkable fault into a casualty.
Can Gas Sensors Detect Lithium-Ion Runaway?
Yes — and earlier than thermal in some environments. The harder questions are which gases, where to mount the sensor, and why we treat it as a complementary layer at sea.
Thermal Cameras vs Thermal Grids — Which Wins on a Cargo Deck?
Both can image temperature. They fail in different places. On a cargo deck the failure modes are what determine the answer.