The short version
- Heat stroke can push body temperature to 106°F or higher within 10 to 15 minutes[2]. On a ship, the cooling has to start before any evacuation does.
- MLC 2006 requires air conditioning for crew accommodation, any separate radio room and any centralized machinery control room, not the engine spaces themselves[3].
- NIOSH limits a new worker to 20% of a normal shift in the heat on day 1, rising by no more than 20% a day[1]. A relief engineer joining in the Gulf in August is that worker.
- NIOSH hydration: 1 cup (8 oz) every 15 to 20 minutes for moderate work, and generally no more than 6 cups an hour[1].
Where heat illness happens on a vessel
Britannia P&I names three places: the working deck in sun and humidity, hot engine rooms, and enclosed spaces with poor ventilation[5]. It flags two groups to watch: new crew members, and crew who come from cooler climates[5].
The law covers some of those spaces and not others. MLC Standard A3.1 requires ships, except those regularly trading where temperate conditions make it unnecessary, to have air conditioning for seafarer accommodation, any separate radio room and any centralized machinery control room[3].
| Space | MLC A3.1(7) air conditioning[3] | What that leaves the operator |
|---|---|---|
| Cabins and mess rooms | Required (cabins and mess rooms also adequately ventilated) | Recovery space exists if it works |
| Engine control room | Required if centralized | A cool refuge next to the hot space |
| Engine room floor plates | Not listed | Managed by work-rest, water and acclimatization |
| Open deck | Not listed | Managed by scheduling and shade |
| Tanks and enclosed spaces | Not listed | Managed by entry planning and time limits |
The US has not ratified MLC 2006, but US ships calling at ratifying ports meet its inspectors. The pattern is the useful part: the regulation protects where crew rest, and leaves where they work to the operator’s heat plan.
Acclimatization: the NIOSH schedule for crew changes
Most heat illness plans miss the crew change. NIOSH‘s schedule limits how much of a normal shift a worker spends in the heat during the first days[1].
| Day | New to heat work[1] | Experienced, returning[1] |
|---|---|---|
| 1 | No more than 20% | No more than 50% |
| 2 | No more than 40% (20% increase per day) | No more than 60% |
| 3 | No more than 60% | No more than 80% |
| 4 | No more than 80% | Up to 100% |
| 5 | Up to 100% | Full duty |
The new-worker column applies NIOSH’s rule of 20% on day 1 and no more than a 20% increase each day after[1]. Britannia gives the same advice in maritime terms: allow acclimatization over several days[5]. On a vessel the practical lever is the watch bill: put a joining engineer on the cooler watch, or pair them, for the first days.
Hours of rest are a heat control too
Fatigue and heat stack. MLC sets minimum rest at 10 hours in any 24-hour period and 77 hours in any seven days, in no more than two periods, one at least 6 hours long, with no more than 14 hours between rest periods[4]. Britannia advises scheduling work away from peak heat hours with frequent breaks in shade[5]. Planning hot-space jobs for the coolest part of the day uses the same rest hours more safely.
Water: how much, how often
- Moderate work under 2 hours: 1 cup (8 oz) every 15 to 20 minutes[1].
- Sweating for several hours: sports drinks with balanced electrolytes[1].
- Upper limit: generally no more than 6 cups an hour[1].
- Water at the work site, not only in the galley: Britannia recommends drinking throughout the day, water or electrolyte drinks[5].
That makes potable water supply a heat control. For storage and quality rules, see vessel potable water and sanitation rules.
Heat exhaustion or heat stroke: telling them apart at sea
| Sign | Heat exhaustion[2] | Heat stroke[2] |
|---|---|---|
| Mental state | Irritability, dizziness, weakness | Confusion, slurred speech, loss of consciousness, seizures |
| Skin | Heavy sweating | Hot, dry skin or profuse sweating |
| Temperature | Elevated | Very high; can reach 106°F or more in 10 to 15 minutes |
| Other | Headache, nausea, thirst, less urine | Medical emergency |
NIOSH first aid for heat stroke: call for emergency care, move the worker to a cool shaded area, remove outer clothing, cool with a cold water or ice bath if possible or wet the skin, circulate air, and place cold wet cloths or ice on the head, neck, armpits and groin[2]. Britannia gives the same cooling sites[5]. At sea, “call 911” becomes a call for medical advice and a decision on evacuation: see when to medevac a seafarer.
Cool first, then call
The 10 to 15 minute climb NIOSH describes[2] is shorter than any helicopter response. The ice, the cold water and the person trained to use them have to be aboard. Stock cold packs and a thermometer that reads high temperatures in the chest; see how to stock a ship medicine chest.
Discovery Health MD writes vessel heat plans with a physician’s sign-off: acclimatization rules in the watch bill, hydration targets and a heat stroke cooling protocol through maritime medical consulting, with the cooling and thermometer supplies stocked through ship medical chest management. Pain and sedation medicines in the same chest stay lawful through controlled substances management. Get a heat plan for your summer routes.
Common questions
What causes heat stroke on ships?
Britannia P&I points to the sunny, humid working deck, hot engine rooms and enclosed spaces with poor ventilation, with new crew and those from cooler climates most exposed[5].
Does MLC 2006 require air conditioning in the engine room?
MLC Standard A3.1(7)(b) requires air conditioning for seafarer accommodation, any separate radio room and any centralized machinery control room, except on ships regularly trading in temperate conditions[3]. The engine spaces themselves are not listed.
How long does acclimatization to heat take?
NIOSH limits new workers to 20% of normal heat exposure on day 1, rising by no more than 20% a day; experienced workers go from 50% to 100% over four days[1].
How much water should crew drink in the heat?
For moderate work under 2 hours, 1 cup (8 oz) every 15 to 20 minutes, and generally no more than 6 cups an hour; use electrolyte drinks if sweating lasts several hours[1].
What is the first aid for heat stroke?
Call for emergency help, move the person somewhere cool, remove outer clothing, and cool fast with cold water or ice, especially at the head, neck, armpits and groin[2].
How quickly does heat stroke become dangerous?
Body temperature can rise to 106°F or higher within 10 to 15 minutes[2]. For the wider data, see medical emergencies at sea.
Do MLC rest hour rules help with heat?
They set the floor: 10 hours of rest in 24 and 77 in seven days[4]. Scheduling hot work away from peak heat within those hours is Britannia’s advice[5].
