Throughout the history of anesthesia, several volatile and flammable agents were commonly used to induce and maintain anesthesia during surgical procedures. These agents, including ether, acetylene, ethylene, and cyclopropane, were highly effective in producing surgical anesthesia but came with significant risks. Fires and explosions were not uncommon due to the flammability of these agents, particularly when combined with the use of oxygen and sources of ignition in the operating room (OR), such as electrocautery, open flames, or static electricity. Although the use of these flammable anesthetic agents has decreased dramatically in recent decades, their history offers valuable lessons in understanding fire risks in the OR.
Ether: The First Flammable Anesthetic
One of the earliest anesthetic agents used in clinical practice, ether (diethyl ether), was introduced in the 1840s and became widely used due to its potency and relatively easy administration. However, ether's high volatility and low ignition temperature made it a significant fire hazard in operating rooms. The first recorded fire caused by an anesthetic agent occurred in 1850, when ether vapor ignited during a facial operation (MacDonald 1994).
Ether was particularly hazardous when used in oxygen-enriched environments, which became standard practice in later years. The combination of ether vapor and elevated oxygen levels made OR fires more frequent. Many reported incidents involved the use of open flames, such as candles or alcohol lamps, igniting ether vapors. Ether explosions were often catastrophic, with some incidents resulting in fatalities or significant injuries to both patients and medical personnel.
As anesthetic technology evolved, the dangers of ether were recognized, leading to the development of safer agents. However, ether continued to be used into the mid-20th century, particularly in developing regions or during wartime when safer agents were less accessible. Eventually, ether was replaced by non-flammable agents, though its legacy remains significant in the history of anesthesia.
Acetylene
Acetylene was introduced as an anesthetic agent in 1923 by Gauss and Wieland in Germany, marketed under the name Narcylen. Although it was potent and provided rapid induction, acetylene was even more explosive than ether: it is unstable under pressure and explosive across a very wide range of concentrations in air or oxygen, so it posed a constant risk of explosion, especially when used in combination with oxygen. Despite its potential advantages over ether, its extreme flammability led to several severe incidents.
Explosions were reported within a few years of its introduction, typically when diathermy (electrocautery) or a spark met the acetylene-oxygen mixture escaping from the breathing system. The sheer danger of acetylene, combined with the availability of less hazardous alternatives, quickly led to its discontinuation in clinical practice.
Ethylene
Ethylene entered clinical use in 1923 (Luckhardt and Carter, Chicago) and gained popularity through the 1920s as an alternative to ether, particularly in North America and Germany. Its potency and lower solubility in blood allowed for more rapid induction and recovery compared to ether. Additionally, its use enabled higher concentrations of oxygen to be administered alongside the anesthetic. However, like ether, ethylene was highly flammable and explosive in the presence of oxygen.
Reports of ethylene explosions began to surface soon after its introduction. The usual pattern was an ethylene-oxygen mixture in the breathing system, or escaping around the mask, ignited by static electricity, an open flame, or cautery. Ethylene explosions were reported throughout the 1920s and 1930s, often with fatal consequences for patients and medical staff (MacDonald 1994).
Despite its effectiveness, the risks associated with ethylene led to its decline in use by the mid-20th century as safer anesthetic agents became available.
Cyclopropane
Identified as an anesthetic in 1929 by Lucas and Henderson in Toronto and brought into clinical use by Ralph Waters in 1934, cyclopropane was hailed as an ideal anesthetic agent due to its potency, ability to induce rapid anesthesia, and the ability to be administered alongside high concentrations of oxygen. However, cyclopropane's flammability posed significant risks. It was explosive over a wide range of concentrations, making it particularly dangerous when used in operating rooms where electrosurgical devices or diathermy were employed.
Cyclopropane explosions were responsible for numerous fatalities and injuries. MacDonald's review notes that the later explosions were far more destructive once oxygen, rather than air, was routinely given with the agent, and that fatal cyclopropane explosions kept being reported year after year even after their causes were well understood. Despite strict safety measures (conductive flooring, antistatic rubber, grounded equipment, humidity control), explosions involving cyclopropane continued to occur well into the 1950s and 1960s, often due to static electricity or faulty equipment.
Cyclopropane remained in use for several decades because of its clinical effectiveness, but its hazards eventually led to its replacement by safer agents like halothane and enflurane. By the 1980s, cyclopropane was largely phased out of use, though it had left a lasting impact on anesthetic practice and safety standards.
Modern Anesthetic Agents and Flammability
The introduction of modern halogenated agents, beginning with halothane in 1956 and followed by enflurane (1972) and isoflurane (1981), marked a significant shift away from flammable anesthetics. These agents were specifically designed to reduce the risks of fire and explosion in the operating room. Although they are generally regarded as non-flammable under clinical conditions, under certain laboratory settings or in extreme oxygen-rich environments, these agents can still ignite. However, the likelihood of fire is vastly reduced compared to earlier agents like ether or cyclopropane. Sevoflurane and desflurane, the agents in everyday use today, are likewise nonflammable at clinical concentrations. The one modern volatile-agent fire hazard sits inside the breathing circuit: sevoflurane reacts exothermically with desiccated carbon dioxide absorbent, and in the early 2000s canister fires were reported with desiccated barium hydroxide lime (Baralyme, since withdrawn), typically in the first case of the day after fresh gas had flowed through the circuit overnight and dried the absorbent. Absorbents without strong bases (potassium or barium hydroxide) do not produce this reaction, which is why they are now standard.
Despite the reduced fire risk with these modern anesthetics, the possibility of fire still exists in the presence of high concentrations of oxygen or nitrous oxide. This is particularly true when energy sources like electrocautery or lasers are used in close proximity to the airway or oxygen-enriched areas. Therefore, strict protocols for oxygen management and fire prevention remain essential in modern anesthetic practice.
