Winter fires combine two opposite threats. Interior work soaks crews in sweat inside heavy turnout gear, then exterior work, water spray and wind chill them fast. Safe cold weather operations rely on early crew rotation, a heated and sheltered rehab area with dry layers and warm fluids, medical monitoring as NFPA 1584 describes, and constant attention to ice underfoot.

Military cold-weather layering rests on one idea: stay warm without getting wet. The Army's COLD rule says keep clothing clean, avoid overheating, wear it loose and in layers, and keep it dry. In practice that means a wicking base, removable insulation, a wind or waterproof shell, and a heavy insulated layer added only when you stop moving.

Cold slows the chemistry inside a battery, so it delivers less capacity and power until it warms up. Battery University reports that a battery giving full capacity at 27 °C typically gives about half at minus 18 °C. The loss is mostly temporary, but charging lithium-ion cells below freezing can cause permanent damage through lithium plating.

Staying warm under body armor is mostly about managing sweat. A carrier blocks ventilation and presses on anything worn beneath it, so the usual approach is a thin, moisture-managing base layer under the armor, insulation added over the kit when you stop moving, and, where policy allows, low-profile heat sources placed so nothing hot is pressed against bare skin.

The Berry Amendment is a US law that bars the Department of Defense from spending its funds on clothing, textiles, food and certain other items unless they are grown, reprocessed, reused or produced in the United States. For textiles, the requirement reaches back through fabric to fibers and yarns. It is codified at 10 U.S.C. 4862 (formerly 2533a) and implemented through DFARS 252.225-7012.

Non-freezing cold injury (NFCI) is damage to nerves, blood vessels and tissue, usually in the feet, caused by hours of cold, wet exposure above freezing. Trench foot and immersion foot are the classic forms. The Army describes risk at air temperatures of 32 to 55 °F, and the CDC notes trench foot can occur up to 60 °F if feet stay wet.

Prehospital hypothermia prevention works in layers: get the patient off cold ground, remove wet clothing, block wind and moisture, add insulation, then add external heat to the torso without direct skin contact. Heat-reflective wraps and vapor barriers limit loss; insulated wraps trap still air; chemical and battery warmers add heat. Military guidance rates simple space blankets as the least effective option on their own.

The lethal triad is the combination of hypothermia, acidosis and coagulopathy in severely injured patients. Each worsens the others: cold slows clotting enzymes, poor perfusion causes acidosis, and uncontrolled bleeding deepens both. Military trauma guidance reports that hypothermic trauma patients die at about twice the rate of similarly injured patients with normal temperature, so heat loss is treated as a threat from the point of injury.

The Hypothermia Prevention and Management Kit (HPMK) is a compact casualty-warming kit used in military and tactical medicine. It pairs a chemical, air-activated heating liner with a hooded, heat-reflective vapor-barrier shell. Medics use it to limit heat loss in trauma casualties during care and evacuation. It is not insulated, so guidelines treat it as a short-term tool.

The Extended Cold Weather Clothing System (ECWCS) Generation III is the US Army's 12-piece, seven-level layering system. Levels 1 and 2 are base layers, Level 3 is fleece, Level 4 a wind jacket, Level 5 soft shell, Level 6 a waterproof shell and Level 7 an insulated parka and trousers. The Army rates the full system for about minus 40 to plus 60 °F.

Cold-weather readiness means solving two thermal problems at once: keeping the team warm, dry and able to use their hands, and keeping casualties from losing heat. Military practice relies on adjustable layering such as the Army's seven-level ECWCS, strict moisture control to avoid cold injuries, and casualty warming kits like the HPMK. Batteries, body armor and procurement rules shape every choice.