Cold Water Immersion and Hypothermia

What the rule requires

Hypothermia is the leading cause of death among shipwrecked crews and other disasters at sea, and the leading cause of death in cold water maritime accidents Boat Crew Seamanship Manual (M16114.5C) Ch. 5 — Environmental Injuries ¶2. It is a lowering of core temperature, and normal internal temperature is 98.6 °F, held there automatically, so even a minor loss may cause incapacitation Boat Crew Seamanship Manual (M16114.5C) Ch. 3 — Cold-Related Factors ¶1. Water carries heat away many times faster than air of the same temperature, which is why the clock runs so much harder on a person in the water than on the same person on deck in the same air USCG Boat Crew Seamanship Manual §4-A.

Two facts about this cut across most of the questions written on the topic. First, "warm" water still does it: survivors in warm water can become hypothermic given long enough exposure, and cold air alone will do it if adequate protective clothing is not worn. Second, the danger does not end at the rescue — survivors removed from the water and left untreated may suffer further critical loss of body temperature, bringing on death after being rescued, and struggling survivors trying to aid in their own rescue may drive their temperature down to unconsciousness or death.

Survival time is not a single number. It turns on water temperature, the physical condition of the survivor, and what the survivor does Boat Crew Seamanship Manual (M16114.5C) Ch. 16 — Water Survival Skills ¶1, and separately on clothing worn, amount of physical exertion and blood alcohol level . Table 16-1 in the reference library gives the bands, and the exam expects you to read it rather than recite it. Know the shape of it: in 32.5 °F to 40 °F water, exhaustion or unconsciousness is expected in 15 to 30 minutes with expected survival 30 to 90 minutes; in 50 °F to 60 °F water, 1 to 2 hours to exhaustion with expected survival of 1 to 6 hours; over 80 °F, indefinite . Sea spray, air temperature and wind chill all increase the threat on top of the water temperature itself.

What you do in the water

Before you go in, if you have any warning at all: put on as much warm clothing as possible covering head, neck, hands and feet; add a PFD if your hypothermia protective clothing has no inherent flotation; button up; turn on signal lights at night; and find your survival whistle. If you must jump, hold your elbows close to your sides and cover your nose and mouth with one hand while gripping that wrist or elbow firmly with the other.

Once you are in:

• Orient yourself immediately — locate the sinking boat, floating objects and other survivors.
• Get out of the water onto anything that floats. A lifeboat, raft, an overturned boat still floating, any platform — this shortens immersion time, and body heat is lost many times faster in the water than in the air.
• Aboard a survival craft, get out of the wind. Water-soaked insulation has already lost most of its value, so a canvas cover or tarpaulin as a wind shield matters, and huddling close to the other occupants conserves body heat.
• Do not swim. The only reasons to swim are to reach a fellow survivor or to reach a floating object you can grasp or climb onto. Unnecessary swimming pumps out the warm water trapped between your body and your clothing, and unnecessary arm and leg movement sends warm blood from the core to the outer layer of the body, producing rapid heat loss.
• Assume HELP — the Heat Escape Lessening Position, and the name mariners have used for it for decades. Float as still as possible, legs together, elbows close to your sides, arms folded across the front of the PFD, head and neck kept out of the water. If you are in a Type III PFD, or if HELP turns you face down, bring your legs together tight, arms tight to your sides, and your head back.
• Huddle with other survivors, making as much body contact as possible. A PFD must be worn to hold either position in the water.
• Do not drown-proof. Letting your head submerge between breaths saves energy in warm water without a PFD, but head and neck are high heat loss areas and must stay above the surface. Without a PFD, tread only as much as is needed to keep your head clear.
• Keep a positive attitude — the will to live extends survival time until rescue arrives.

You are in 55 °F water 300 yards from a beach, wearing a Type I PFD, and no rescue is in sight. Do you swim in?

No. Swimming typically reduces a person's chance of survival through more rapid loss of body heat, and unnecessary swimming pumps the warm water out from between your body and your clothing. The exception in the manual is narrow: swim only to reach a fellow survivor or a floating object you can grasp or climb onto. Float still in HELP, head and neck out of the water.

Reading how far it has gone

Shivering is the sign candidates trust and the one that misleads them. A hypothermic person will tremble and shiver, but these symptoms may not always be present, and when a person stops shivering the hypothermia may have advanced beyond the initial stages .

The progression runs from intense uncontrollable shivering and impaired ability to perform complex tasks, through violent shivering, difficulty speaking, sluggish movement and the onset of amnesia, to shivering being replaced by muscular rigidity, impaired coordination, erratic and irrational behaviour, stupor, then loss of contact with surroundings, slowing pulse and respiration, and failure of heart and lungs . Level of consciousness becomes clouded as body temperature approaches 90 °F, and consciousness is generally lost at 85 °F.

A moderately hypothermic person manifests the symptoms of an intoxicated person — slurred speech, poor coordination, clouded thinking. Survivors taken aboard on a SAR case who appear drunk are treated as hypothermic until proven otherwise.

Core temperature is the most useful yardstick, and only a rectal temperature reflects it; oral, auxiliary and extremity temperatures do not. The manual then closes that door: do not attempt to take rectal temperatures in the field. Treat the patient as the visible signs and symptoms suggest, and begin treatment if the skin feels cold to the touch.

Handling and treating a recovered casualty

When critical hypothermia is suspected, the rescue itself is conducted to avoid rough handling and to minimise the victim's exertion — send a surface swimmer into the water to assist the survivor into the rescue craft rather than have them climb. Excessive movement may cause heartbeat irregularities which can be fatal. Keep the patient calm and quiet during the rescue and afterwards, and allow no physical activity beyond what is absolutely necessary, because exertion burns the body heat needed to bring the core temperature back up. A cold-stressed heart is irritable, so move and lift the person as horizontally and gently as possible .

Treatment then splits on the condition of the patient. A survivor who is rational and able to recount their experience, even while shivering dramatically, generally needs only wet clothes removed and replaced with dry clothes or blankets, and a warm place to rest Boat Crew Seamanship Manual (M16114.5C) Ch. 5 — Environmental Injuries ¶3.

For a semiconscious or near-death victim, contact a medical facility as soon as possible and administer first aid while awaiting instructions:

1. Avoid rough handling. Check for breathing and heartbeat; begin CPR immediately if both are absent. If breathing and pulse are present, transfer the person gently to a warm environment and check breathing and heartbeat frequently. Activate EMS.
2. Lay an unconscious or semiconscious victim face up with the head slightly lower than the rest of the body. If vomiting occurs, turn the head to one side and clear secretions from nose and mouth.
3. Remove clothing with minimum movement of the body, cutting it away if necessary. If the patient cannot be taken somewhere they can be warmed with blankets, dry clothing or other means, do not remove wet clothing — under those circumstances wet clothing is better than no clothing.
4. Give nothing orally, especially alcohol.
5. Insulate with a blanket. Do not aggressively rewarm an unconscious or semiconscious victim; rapid warming causes dangerous complications. The primary objective after removal from the water is to prevent the person from getting colder.
6. If trained and equipped, administer warm, humidified oxygen by face mask, which also rewarms the internal core.
7. Where transport to hospital will be delayed, begin gentle rewarming: heating pads or hot water bottles under a blanket at the head, neck and groin, or direct body-to-body contact with a blanket wrapped around both of you. Hypothermia patients are very prone to burns and hot packs may cause third degree burns.
8. Treat for shock, and evacuate to a medical facility during or soon after emergency treatment.

Do not rub the limbs, and do not give alcohol. Both drive cold blood back to the core and can cause a dangerous drop or a heart rhythm problem. Check a hypothermic pulse for a full 30 to 45 seconds, because it may be very slow and faint, and hold to the guiding rule: a hypothermia victim is not considered beyond help until they have been rewarmed .

A near-drowning survivor may look recovered and deteriorate hours later, so shortness of breath, coughing or blueness appearing after rescue is an emergency, and monitoring of breathing, pulse and level of consciousness continues until care is transferred USCG Boat Crew Seamanship Manual §4-B.

Telling it apart

Four garments serve as hypothermia protection, and the exam separates them on one criterion: does the garment float you by itself, and how much in-water exposure is it built for Boat Crew Seamanship Manual (M16114.5C) Ch. 6 — Hypothermia Protective Clothing ¶1.

• Immersion suit — floats you and gives excellent hypothermia protection; the recommended PFD when abandoning ship, worn even if you can board the raft directly from the ship. Not a working outfit, because dexterity in it is limited Boat Crew Seamanship Manual (M16114.5C) Ch. 6 — Hypothermia Protective Clothing ¶2.
• Dry suit — no inherent buoyancy at all; a PFD must be worn over it at all times while underway. With thermal underwear layered beneath, it gives the best protection in adverse weather and cold-water immersion. A dry suit is not a PFD.
• Anti-exposure coverall — is itself a Type V PFD with flotation similar to a Type III, and it is the standard garment for moderate weather in closed-cockpit boats. Good out-of-water protection, limited hypothermia protection in the water; wear a dry suit instead when more than periodic exposure is anticipated. Do not wear a PFD over it — the extra buoyancy can stop you swimming out from under a capsized boat.
• Wet suit — not authorized for boat crewmembers. Cutter surface swimmers may wear it; it protects against cold water but will not keep the wearer dry.

Requirement and waiver: hypothermia protective clothing is worn in heavy weather or hazardous operating conditions. A Unit Commander may waive it case by case where the risk is minimal, such as non-hazardous daylight operations in calm water, and when a waiver is granted the clothing must still be carried aboard. Coxswains shall require it donned for heavy weather or hazardous operations, recovery of a person from the water and helicopter operations among them. Figure 6-4 pairs air and water temperature: read across at the water temperature, up at the air temperature, and don what is shaded where they intersect.

Working a question

You are coxswain, water 48 °F, air 40 °F. A PIW in a Type I lifejacket has been in the water an estimated 35 minutes. He is shivering violently, speech is slurred, and he cannot tell you the name of his boat.

1. Read the water temperature against the table. In 40 °F to 50 °F water, exhaustion or unconsciousness is expected in 30 to 60 minutes. He is inside that window, so this is a critical hypothermia case, not a wet passenger.
2. Read the symptoms, not the temperature. Violent shivering with difficulty speaking and the beginning of amnesia is well past the first stage. Do not attempt a field temperature.
3. Get him aboard without letting him work. Put the surface swimmer in the water to assist him into the boat. Every yard he climbs is body heat he needs to rewarm with.
4. Handle him gently and keep him horizontal. Excessive movement can produce fatal heartbeat irregularities.
5. Decide the wet clothing question on what you can offer instead. If you have a warm compartment with blankets or dry clothing, remove the wet clothing with minimum movement. If you have neither, leave it on — wet clothing beats no clothing.
6. Nothing by mouth. He is slurring and disoriented, so he is not fully alert; no coffee, no soup, and never alcohol.
7. Insulate and rewarm slowly. Wrap him in a blanket; the objective is to stop him getting colder. Warm humidified oxygen if you carry it and are trained. Hot water bottles at head, neck and groin only if evacuation will be delayed, with care against burns.
8. Treat for shock, monitor, hand over. Watch breathing, pulse and level of consciousness, be ready for CPR, and pass the immersion time and his condition on arrival to the medical responders USCG Boat Crew Seamanship Manual §4-B.

Where candidates lose the point

• Answering that a strong swimmer should make for the boat or the beach. It reads like initiative, and initiative is usually the right answer elsewhere on the exam. Here swimming typically reduces the chance of survival through more rapid heat loss, and the manual permits it only to reach a survivor or a floating object.
• Stripping all wet clothing off, always. The rule is conditional. Remove it only if dry clothing, blankets or another warming method is available; otherwise the wet clothing stays on.
• Something warm to drink. Warm sweet drinks go only to a fully conscious person who can swallow. Semiconscious and unconscious persons get nothing to eat or drink, and alcohol goes to no hypothermia victim ever.
• Treating "no longer shivering" as improvement. When a person stops shivering, hypothermia may have advanced beyond the initial stages, and shivering being replaced by muscular rigidity is a later-stage sign.
• Stopping care on a cold, pulseless casualty. A hypothermic pulse may be very slow and faint, so check for a full 30 to 45 seconds, and treat no hypothermia victim as beyond help until they have been rewarmed.
• Putting a PFD over an anti-exposure coverall, or treating a dry suit as flotation. The coverall is already a Type V PFD and the added buoyancy can prevent the wearer swimming out from under a capsized boat; the dry suit has no inherent buoyancy and requires a PFD over it at all times underway. The two garments pull in opposite directions, and that is exactly why the pair is written into questions.

Check yourself

Three survivors are in 45 °F water together, all in Type I lifejackets, waiting on your boat. What position do you tell them to take?

Huddle — close together with as much body contact as possible. Where a single PIW uses HELP, multiple survivors conserve heat by huddling. A PFD must be worn to hold either position, which they have.

You take a man aboard who smells of nothing, is unsteady, slurring and belligerent, and your crewman says he is drunk. Your assessment?

A person moderately hypothermic will manifest the symptoms of an intoxicated person, and survivors taken aboard on a SAR case often appear to be under the influence. Treat him as hypothermic, gently, and begin treatment if his skin is cold to the touch.

You are dressing crew for a training run in cold water where the surface swimmer will enter the water. Which garment for the crewmembers on deck, and which is not an option?

A dry suit with layered thermal underwear and a PFD over it gives the best protection against cold-water immersion. A wet suit is not authorized for boat crewmembers; it may be worn by a cutter surface swimmer. The anti-exposure coverall is the moderate-weather closed-cockpit garment, intended only for periodic exposure.

Your semiconscious hypothermia casualty is 90 minutes from the nearest hospital by boat. Do you begin active rewarming?

Gentle rewarming only, and only because of the delay: blanket with heating pads or hot water bottles at head, neck and groin, or body-to-body contact under a blanket. Do not attempt aggressive rewarming of an unconscious or semiconscious victim, because rapid warming causes dangerous complications, and hypothermia patients burn easily from hot packs.

Abandoning ship is ordered and you can step directly into the raft from the deck. Do you still don the immersion suit?

Yes. The immersion suit is the recommended PFD when abandoning ship and should be worn even if boarding the life raft directly from the ship is possible. Stow sharp objects and remove footwear first to avoid puncturing or tearing it, and don it in pairs with another crewmember.

A crewman falls overboard from the bow and swims 20 yards back to the boat, then climbs the ladder unaided in 50 °F water. He says he is fine. What is the concern?

Exertion. Struggling survivors trying to aid their own rescue can drive their body temperature down, and no physical activity beyond the absolutely necessary should be allowed, because exertion consumes the heat needed to raise core temperature. Get him out of the wind, into dry clothing and a warm space, keep him quiet, and monitor him.

You have no PFD on a man in the water and he tells you he will conserve energy by drown-proofing. Correct him.

Drown-proofing — relaxing and letting the head submerge between breaths — is an energy saver in warm water only. Head and neck are high heat loss areas and must stay above the surface, which is why a PFD matters more in cold water. Without one, tread only as much as needed to keep the head clear.