Posted by byager | Fire and Rescue, General, Health, PPE, Performance, Safety
Monday, May 3rd, 2010 7:05 am

Steam burns and reflective trim

Steam or scald burns (especially the forearms) are almost a daily occurrence throughout the fire service. Sometimes, steam burns can even cause catastrophic damage when wet gear is exposed to fire ground heat for some period of time, and then compressed against the fire fighter’s arm. Why?

1. Fire ground temperatures. Fire fighters immerse themselves in radiant heat loads ranging from 120°F to 300°F for extended periods of time and to radiant blasts of short duration ranging from 600°F to 1500°F. Exposures to flame contact, including flashovers, can range up to 2200°F.

2. Tactics. When fire fighters are attacking, their hands are out front, either on a crawl or gripping their hose lines and tools. Their hands and arms see the most heat, but often don’t feel it until it’s too late.

3. Water, the Double-Edged Sword. The hose team, wrapped in a tug-of-war with a charged line, cannot avoid getting drenched. Fog blasts from the nozzle are directed to the heat source; often just to suck up some heat so the attack team can get closer. It’s true that water replaces air and puts out fires but, unfortunately, water conducts heat 21 times faster than air. That’s why the NFPA Standard has a water resistance requirement for outer shells, and that’s why a moisture barrier is required.

4. Garment Fit. Turnout coats are usually 8” to 16” bigger in circumference than the fire fighter’s body in the chest and waist. But they’re only 3-4” bigger around the forearms and biceps. All trained fire fighters know the trick of “wiggling” when they feel “tingling” from heat in order to avoid contact burns. But, the arms don’t allow much wiggle room and, besides, their arms are too busy to “wiggle”. Contact between the wet garment and the body is sometimes inevitable.

5. Heat Expands Water. When heated, water expands (1700% for actual steam). The more water in the sleeve end, and the longer it’s exposed to heat, the greater the pressure generated by super heated water. To vent itself, steam will take the path of least resistance.

6. Trim. Retroreflective and fluorescent trims are a major safety enhancement to fire fighter turnout gear because they provide visibility during low light and daylight fire ground conditions respectively. But there are some tradeoffs:

  • Trim is dense, so it absorbs and holds heat.
  • Trim is solid with no insulating air, so it conducts that heat very efficiently.
  • Trim is impermeable and is the outermost layer, so it traps heat and water underneath itself.

Unfortunately, trim offers the most resistance (it’s totally impermeable); so it increases the expansion rate in all other directions. When the sleeve is compressed (such as during the attack position), scalding heat is transferred quickly and efficiently by superheated water under the trim. It can either escape by moving laterally under the trim and outward then upward through about 1/4” of compressed gear, or it can move inward toward the skin, even through the vapor permeable moisture barrier.

When that water in the system touches the skin at a temperature of 162°F, a third degree burn will happen instantaneously. No tingle. Although water doesn’t become steam until 212°F, just a five-second exposure to 140°F fluid temperature under stored energy conditions can cause third degree burns.

Turnout manufacturers have spent considerable time and resources to develop a solution to the trim problem. Several initiatives have emerged:

1. Some have suggested eliminating trim from the arm area. The downside to this suggestion is reduced visibility and it does not address steam burns in other locations where trim is present.

2. Another suggestion is staggering the trim to maintain a channel for nerves and blood supply should a firefighter receive severe steam burns. This suggestion only relocates the injury into a different pattern instead of reducing the risk or rate of steam burns.

3. The recommendation of removing trim altogether and replacing it with a printed or silkscreened reflective pattern is gaining support. Current material limitations of printed patterns, however, have several shortcomings. Print patterns have durability issues (especially relating to abrasion) and do not adequately address the fluorescent daytime visibility problem.

4. An extra layer of moisture barrier material positioned somewhere under the trim can provide a little extra TPP, but doesn’t alleviate the real problem; the entrapment of rapidly expanding moisture under the impermeable outer layer of the composite. If the additional layer is an impermeable steam blocker itself, and is deep in the composite, it can offer some help.

5. The most recent initiative, which appears to have no downside, is perforating the trim. Perforated trim is ventilated with hundreds of tiny holes. Even though these points of ventilation are small, the trim becomes more breathable than the moisture barrier. This changes the direction for heated and expanding water and provides “escape valves” for releasing the wet heat during the build up of stored thermal energy. Perforated trim creates a path to expel heat outward instead of inward toward the body. This should help reduce some burns that can occur under the trim when gear is wet and compressed.

The only sure-fire way to eliminate steam burns or scald injuries would be to avoid the combination of water and heat altogether… not a very realistic option in your line of work. But, reducing the likelihood, severity and frequency of scald burns in high-risk areas (like underneath reflective trim) is quite possible. Turnout manufacturers and their industry suppliers are continually exploring new technology or pushing the boundaries of current technology to find creative answers to problems like steam burns.

One Response to “Steam burns and reflective trim”

  1. Didn’t know that Steam burns can cause so big damage. Now I know what to do in such situations. Thanks for explanation