How Are Thermal Hotspots Detected?
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.]
Questions, answered
Is measuring temperature the hard part of detecting hotspots on a cargo deck?+
No. IR measurement is solved engineering. The hard parts are the next two questions: distinguishing anomaly from noise, and distinguishing anomaly from a real thermal event. That is where detection products actually differ.
Why not just trip on an absolute temperature threshold?+
Because ambient drifts too much. Engine bays cool unevenly, solar gain through deck openings can add 10–15 °C on coastal sailings, and ambient varies around 30 °C across a single voyage. A static trip is the simplest and worst-performing rule. A per-cell rolling baseline (EWMA) that trips on sustained delta-from-baseline is robust to that drift.
How does the system avoid false alarms from sunlight?+
With a cross-cell coherence check. Solar gain is shared by neighbouring cells, so if neighbours share the delta it is suppressed as environmental; if the delta is local to one cell it escalates. Coherence is the suppression layer, not the detection layer.
How fast does a real event reach the bridge?+
The end-to-end budget is under 4 seconds from measurement to a bridge red-state, with the sensor-to-segment-master poll under 8 ms and a roughly 3-second coherence confirmation window. Against ceiling smoke detection, bench data shows 18–25 minutes of lead time.
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 a small fault into a casualty.
Can Gas Sensors Detect Lithium-Ion Runaway?
Yes — and earlier than thermal in some settings. The harder questions: which gases, where to mount the sensor, and why it's a complementary layer at sea.
Thermal Cameras vs Thermal Grids at Sea
Both can image temperature. They fail in different places. On a cargo deck the failure modes are what determine the answer.