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CBRNE - Incendiary Agents, Magnesium and Thermite
Updated: Aug 6, 2008
Introduction
Background
Two major types of metal incendiaries exist, those that are magnesium based and those of the thermite/thermate type. Incendiary metals are usually encountered in the military or industrial setting but can also be encountered in other applications due to common usage of magnesium shavings as a fire-starting technique such as for camping or in sparklers and fireworks.
Magnesium, a silvery white metal of atomic weight 24.32, ignites at 632°C and burns at 1982°C, with magnesium oxide (MgO) as its combustion product. In an exothermic reaction, metallic magnesium can ignite to produce magnesium dihydroxide (ie, Mg(OH)2 and hydrogen. When combined with water while burning it releases hydrogen gas and oxygen. Magnesium is used in either powdered or solid form as an incendiary agent for both illumination and antipersonnel purposes. Various alloys of magnesium (eg, aluminum/zinc/magnesium alloy found in US M126 round) are mechanically sturdier but also can be ignited easily. Militaries use magnesium in hand-held signal flares and in glowing “tracer rounds,” which are ammunition fired in series with traditional ammunition in automatic weapons to assist with aim (eg, US M856, M10, M17).
Thermite is a mixture of powdered or granular aluminum and powdered iron oxide. When combined with other substances, such as binders, the material is termed a thermate. All such materials react vigorously when heated to the combustion temperature of aluminum. This reaction produces aluminum oxide, elemental iron, and sufficient heat to melt the iron. The reaction temperature is at least 2200°C. Due to its high temperature and creation of iron, the thermite is used industrially for welding such as welding together railroad track and other in place structural repairs.
Thermite is also used to purify other metals through its high temperature. The military uses thermite in grenades (US AN-M14) for the destruction of vehicles and equipment where their high heat renders vehicles and equipment inoperable. Possible thermite burns could be seen from a railroad employee opening the thermite crucible before the reaction had completed and being exposed to the still burning material or a military individual being exposed to the burning particles from the use or demonstration of one of these grenades.
Because the burning temperature of these chemicals is so high, standard hazardous-materials clothing (even level A self-contained and chemical-proof clothing) is not protective.
Pathophysiology
Burning thermite or magnesium produces predominantly thermal injury that may be considered identical to deep partial- or full-thickness thermal burns (see Burns, Thermal), but residual particles (especially of magnesium) may produce chemical injury to the eyes, skin, and respiratory tract. The magnesium particles can react with tissue fluid to create magnesium hydroxide, which is a strong base. This strong base can lead to alkali burns from the noncombusted magnesium particles. In a separate reaction while the magnesium is burning, it can react with water to create hydrogen gas (H2), which is highly flammable. This is why water is not a recommended dousing agent for these kinds of burns. If exposure to incendiary metals takes place in a small, confined space such as in a military vehicle attacked by a thermite grenade, inhalation of hot gasses can produce direct thermal injury to respiratory tissues.
Frequency
United States
No exhaustive study or series of incendiary injury exists. In a study of one burn center during a 51-year period, only one burn was attributed to magnesium and no burns were reported due to thermite. This seemingly low incidence likely stems from the fact that all thermal burns are managed similarly regardless of cause and often unique historical elements go unnoticed or unrecorded.
Mortality/Morbidity
Outcomes of incendiary metal burns are similar to other thermal injuries (see Burns, Thermal).
Race
Incendiary burns show no predilection for race.
Sex
Because incendiary metals are more commonly encountered in industrial and military settings, exposures are more common in males than in females.
Age
Because incendiary metals are more commonly encountered in industrial and military settings, exposures are more common in younger adults.
Clinical
History
The history usually makes the nature of the exposure evident, as the patient or rescuer describes the circumstances leading to exposure to thermite or magnesium incendiaries.
- In the event that a patient presents with burn injury and is unable to give a history, consider exposure to magnesium, thermite, or other hazardous materials.
- Obtain the patient's relevant medical history. In decision-making, consider diseases (eg, diabetes mellitus, vascular disease) that may affect healing as well as drug allergies.
Physical
Incendiary agents produce predominantly dermatologic and respiratory effects.
- Vital signs
- As with all resuscitations, first priority is to maintain and support airway, breathing, and circulation (ABC). Patients with airway burns or significant fume exposure may require endotracheal intubation and ventilatory support. Acute respiratory distress syndrome (ARDS) may develop.
- Patients with significant dermal burns require aggressive fluid resuscitation, following a formula, such as the Parkland burn resuscitation guidelines, and require monitoring of urinary output and other vital signs.
- Inhalation of magnesium dust or magnesium oxide smoke can produce respiratory irritation with the following potential signs and symptoms:
- Nasal catarrh
- Productive cough
- Pneumonitis, including metal fume fever
- ARDS
- Hypoxia and tachypnea
- Airway burns (eg, edema, charring) or lung burns, with potential airway obstruction
- Wheezes or crackles on lung examination
- Unique features of incendiary metal burns are as follows:
- Thermite burns can deposit molten iron in tissue resulting in very extensive if localized tissue damage. Clinicians should assume that these burns are deep partial- or full-thickness until proven otherwise.
- Magnesium particles can react with tissue fluid to produce magnesium dihydroxide, which produces an alkali chemical burn in addition to direct thermal effects.
- Retained magnesium particles in skin may produce a lesion that mimics gas gangrene, with tissue death and intratissue gas bubbles due to hydrogen gas formed from the same reaction.
- Ocular examination
- Incendiary metals emit intensely bright light in the infra-red, visible, and ultraviolet spectra. Tactical military uses include temporarily night blinding of adversaries. The intense light emitted by incendiary metals in military and industrial settings can cause ultraviolet (UV) keratitis. Staining with fluorescein and examination with a slit lamp will confirm such injuries. The fluorescein staining will show diffuse punctuate corneal lesions, which generally have a discrete lower border where the lower lid protected the rest of the cornea. Patients generally complain of photophobia, decreased visual acuity, foreign body sensation.
- The eyes must also be examined to determine if any significant amount of magnesium dust was deposited on the corneas. This can also be seen with a slit lamp and will determine if any cleaning of the corneas or urgent ophthalmological referral needs to take place.
Causes
While exposure to incendiary metals can occur in many settings, serious burns are most likely related to industrial or military incidents. Most of the lung injury would occur if a person were trapped in a confined space with one of these burning substances.
- Common
- Sparklers
- Road/maritime flares
- Campfire starters
- Industrial
- Welding
- Metal purification
- Military
- Thermite grenades
- Flares
- Tracer rounds
- Miscellaneous - Terrorist explosives
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References
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Further Reading
Keywords
incendiaries, incendiary agents, magnesium, thermite, metal incendiaries, Mg, thermate, thermal burn, thermal injuries, chemical warfare, magnesium burns, thermite burns, magnesium injury, thermite injury
