A car deck at sea is watched by a heat detection cable along the deckhead and carbon monoxide sensors along the bulkheads, because a vehicle left running in a closed deck is a fire and a poisoning at once. On the night crossing, bay 2C, which is empty, reads the heat of a warm engine and the exhaust of an idling one, for the whole passage, and the deck fans run to clear it.
I am the bosun, and the car deck at sea is my round.
How the deck is watched.
A linear heat detection cable runs the length of the deckhead over every lane, and it reports a temperature at every point along it, so a hot vehicle shows as a warm spot at a known position. Carbon monoxide sensors sit along the bulkheads at breathing height, and the deck fans run on their readings, because a running engine in a closed deck poisons the air in minutes.
Vehicles are switched off and left in gear, and the round confirms it: every vehicle, every crossing, engine off, and the deck lights are dimmed, and the doors are shut.
On the night crossing, bay 2C reads a warm engine and an idling exhaust.
2C is the after end of lane 2, and it is empty on the night crossing, because the loading officer leaves it empty, because of this.
The heat cable shows a warm spot over 2C at the temperature of a car's bonnet with a warm engine under it. The gas sensor nearest 2C shows carbon monoxide at the level an idling petrol engine makes in a closed deck, and the fans run to clear it, and it does not clear, because it is being made.
For the whole crossing. It starts when the doors shut and stops when they open, and in between the deck is watched by a camera that shows bay 2C empty, in dim light, with the fans running over nothing.
What has been checked.
The cable, which has been tested with a heat gun at 2C and reads the gun's heat exactly where the gun is, and reads the warm spot when the gun is not there.
The gas sensor, replaced, and cross checked with a handheld meter carried down to 2C on the crossing.
The handheld read carbon monoxide at 2C. In my hand, in an empty bay, at the level that makes the fans run, and the air there smelled of exhaust, and the deck plates under 2C, when I put my hand flat on them, were warm, in the shape of a car, which I could trace with my palm, and cold outside it.
What the fans do.
They run all night on the night crossing because the sensor says they must, and the fan hours are on the maintenance log as excess, and the engineers have asked why the car deck fans do a night crossing's worth of running for a deck that the camera says has nothing running on it.
I have told them. The chief engineer came down with me on a crossing and stood in 2C with the handheld and the smell and the warm plates and said nothing for a while and then said that he would put the fan hours down to sensor sensitivity, and he has.
The camera.
The deck camera records on motion and it does not record 2C on the night crossing, because nothing moves there.
Except that the recording from one crossing in the winter has, for four seconds at about the middle of the passage, the camera's exposure adjusting, the way it does when a light comes on in its field, and in those four seconds the deck plates in bay 2C are lit from about a foot above them, in two pools, the way the plates are lit by a car's headlamps when somebody sitting in a parked car switches them on to see, and switches them off.
What is done about it.
2C is left empty on the night crossing, by the loading plan, which says the bay is reserved, and the fans run, and the log says sensor sensitivity, and the port inspector, who has read the fan log, has been satisfied by the chief's note.
What I do.
I do the round.
The one thing I have changed is that on the night crossing I do not walk down lane 2 to the after end.
I do the round from the other lanes and I look across at 2C from lane 3, and the reason is the crossing when I walked down lane 2 with the handheld and stopped at the edge of 2C, in the warm, in the exhaust, and heard, from about where the driver's window of a car parked in that bay would be, a window wind down.