Br. J. Surg. Vol. 63 (1976) 981-983
Inflammable antiseptics and theatre fires C . E . B R I S C O E , D. W . H I L L A N D J . P . P A Y N E * SUMMARY
This paper describes an investigation designed to find out if theatre fires could be started by the antiseptic painted on the patient's skin being ignited by cautery or diathermy. It was found that hot wire cautery or diathermy generated enough heat to ignite all alcohol-based antiseptics even if these contained as little as 20 per cent alcohol. They could also cause iodine to explode in the presence of nitrous oxide, and nobecutane to explode in the presence of nitrous oxide or increased oxygen. The likelihood of these combinations causing fires is discussed, and it is recommended that when diathermy or cautery is to be used near the surface of the body, either an aqueous-based antiseptic is used or if spirit solutions are required they are carefully dried of before proceeding. THEoccurrence of minor fires around the bodies of patients during surgical procedures continues to be reported (Magruder and Guber, 1970; Elkington, 1971); and stories of unreported fires abound. These fires are often associated with the use of cautery or diathermy on the body surface. The possibility that these instruments might ignite the surgical drapes was investigated by Cameron and Ingram (1971), but the initial cause of such fires may be ignition of the antiseptic painted on the patient's skin which subsequently ignited the drapes. An experiment was therefore designed to mimic the conditions under which these fires occur. The temperature at which the commonly used antiseptics were ignited by a hot wire was investigated both in air and in an atmosphere of anaesthetic gases such as might be encountered when the patient's expiratory valve lies close to the operation site. These temperatures were then compared with those encountered in clinical practice.
Materials and methods A brass fire box (5 cm diameter) was constructed with an electrically heated nichrome wire spiral built into it. This wire was connected to a variable resistance enabling the temperature to be varied from room temperature to over 1200 "C. A chromel-alumel thermocouple was spot-welded on to the surface of the wire and connected to a voltmeter reading in mV. The temperature at the surface of the wire was then obtained from reference tables and the figures were checked on an optical pyrometer. In order to introduce various gas mixtures, one end of the fire box was connected to a gas supply from an anaesthetic machine while the other end was open, allowing the gas to flow across the hot wire. The gas
passed through a water trap to avoid a flashback explosion and the oxygen concentration was measured in a Servomex oxygen analyser. The antiseptics and materials to be tested were introduced on a copper saucer of 1.3cm diameter with a long handle, and the surface of the liquid or solid material was placed as close to the rod as possible without touching it. The rod was then maintained at increasing temperatures for 30 seconds at a time until ignition occurred. The time to ignition and the ignition temperature were first recorded in air, and then in varying mixtures of nitrous oxide and oxygen, ending with 100 per cent oxygen. Several of the antiseptics tested were in a 70 per cent alcohol mixture and the effect on the ignition temperature of diluting the alcohol was investigated. The possibility that the ignition point might be influenced by a patient's expiratory valve blowing on the substance was examined by increasing the gas flow through the fire box.
Results Table I shows the temperatures of the wire required to ignite the substances tested, first in air, then in 30 per cent oxygen and 70 per cent nitrous oxide, and finally in 100 per cent oxygen. The antiseptics based on 70 per cent industrial alcohol ignited at around 900 "C, but up to 90 "C lower than this in the nitrous oxide/ oxygen mixture and a few degrees lower still in 100 per cent oxygen. The antiseptics in aqueous solution would do no more than smoulder without supporting a flame and they only did this at temperatures of lo00 "C or over. Two substances exploded. One was iodine at 820 "C in the presence of nitrous oxide, and the other was nobecutane in both the nitrous oxide/oxygen mixture and in 100 per cent oxygen at 820 and 790°C respectively. The temperatures at which the surgical drapes, sterile paper, green towels and gauze ignited are also shown. These are all lower than for the fluids, lying between 730 and 770 "C, and showed a marked drop in the presence of nitrous oxide and oxygen to below 500 "C. Soaking these materials in the ignitable antiseptics resulted in their ignition temperatures rising to nearer the ignition temperatures of the fluids. The length of time before ignition proved not to be an important consideration. All the substances ignited within 15 seconds if they were going to ignite and if
* Anaesthetic Research Department, Royal College of Surgeons, London. Present address of C. E. Briscoe: Norfolk and Norwich Hospital, St Stephen's Road, Norwich. 981
C. E. Briscoe et al. Table I: TEMPERATURE OF IGNITION OF VARIOUS ANTISEPTICS
In air
Substance
Chlorhexidine and cetrimide in 70% alcohol (Savlon) 915 Chlorhexidine digluconate in 70% alcohol (Hibitane) 920 Iodine in 70% alcohol 930 Proflavine in 70% alcohol 890 Thiomersal in 50% alcohol (Merthiolate) 920 Chlorhexidine digluconate in aqueous solution (Hibitane) No ignition Chloroxylenol in aqueous solution (Dettol) N o ignition Povidone-iodine in aqueous solution (Disadine, Betadine or Pevidine) No ignition 890 Nobecutane Gauze Green towels Sterile uauer
780 770 720
Table 11: TEMPERATURE OF IGNITION OF VARYING DILUTIONS OF CHLORHEXIDINE AND CETRIMIDE IN ALCOHOL Ignition temperature ("C) In 30% oxygen/ Alcohol W ) In air 70% nitrous oxide In 100% 0. 825 70 870 870 60 50 40 30 20 10
880 890 880
940*
870 870 870 870 940 990*
850 850 850 870 890
*
* Flame not supported. Table 111: EFFECT OF GAS FLOW ON IGNITION TEMPERATURE OF CHLORHEXIDINE AND CETRIMIDE IN 70 PER CENT ALCOHOL Flow of air: No flow Ignition temperature ("C): 1 litre/min 2 litres/min 4 litreshin
890 890 920 930
the temperature was then raised 20 "C they could be guaranteed to ignite within 3 seconds. An attempt was made to ascertain how much dilution of the alcoholic antiseptics would be needed to prevent them igniting and the results are shown in Table II. In fact, flames were supported at all dilutions down to 20 per cent alcohol if nitrous oxide and oxygen were present, although the ignition temperatures were a little higher at these dilutions. Table 111 shows the effect of increasing the gas flow through the fire box. Raising the gas flow from zero to 4 litres/min resulted in the temperature of the wire having to be raised 40 "C to ignite the same material. Discussion Fires are a very alarming and unexpected complication of a surgical procedure. A number of these fires occur when non-inflammable anaesthetic gases are in use, and they often happen when diathermy or hot cautery is being applied to, or near, the surface of the body. Cameron and Ingram (1971) demonstrated that the surgical drapes could be ignited by a hot wire cautery, but these are usually removed from the site of surgery and the fires may well be initiated by the vapour from antiseptic catching fire. The heat of the skin will 982
Ignition temperature ("C) In 30% oxygen/ 70X nitrous oxide In 100% 0, 870 840 820 (explodes) 880 890
N o ignition 970 (smoulders) I100 (smoulders) 820 (explodes) 485 485 520
825 820 820 870 890
N o ignition 970 (smoulders) I 1 0 0 (smoulders) 790 (explodes) 460 460 490
ensure that this is in high concentration near the operation site. Thus, a fire known to one of the authors occurred after a surgeon painted the abdomen with chlorhexidine digluconate, opened the skin with a knife and then started to cut deeper layers with the diathermy. Another broke out while perineal warts were being cauterized after painting with a spirit solution. The two fires reported during ophthalmic operations (Magruder and Guber, 1970; Elkington, 1971) make no reference to the surgical painting, but they may also have been triggered in this way. Five cases reported by the Medical Defence Union (1956/7, 1961, 1971, 1975) were definitely ascribed to this cause. That fires could develop in this way is demonstrated by the results obtained in this paper. The ignition temperatures for these fluids of 800-900°C are the temperatures that would be obtained by a cautery glowing a cherry red colour (Newnes, 1972). Various manufacturers were in fact asked to state what temperatures their hot wire cautery could reach, but none was prepared to state a temperature as they said there were too many variables such as age and state of the rod or wire in use. There is, therefore, n o way of guaranteeing that a cautery will not reach the above temperatures, and the temperatures obtained by a diathermy arc are, of course, much higher. The temperatures measured in these experiments are considerably higher than the conventionally measured ignition temperatures. For instance, the ignition temperature of industrial methylated spirit in air is reported as 365 "C and cotton as 254°C (Zabetakis, 1965), but these are measured by raising the temperature of the whole substance until spontaneous ignition occurs. A different set of circumstances arises when substances are exposed to a spark or hot wire. In this case, which is the clinical situation, the temperature source is small and the ignitable material comparatively large. Conduction and convection can then reduce the amount of material exposed to the temperature to amounts that prevent the oxidative reactions of combustion taking place, unless the source temperature is considerably higher than that of a complete environment that would bring about ignition. Wind increases the convection and, as the results demonstrate, raises the ignition temperature.
Inllammable antiseptics and theatre 6res An atmosphere of nitrous oxide or oxygen slightly decreases the ignition temperature but greatly increases the rate of burning and heat of combustion once ignition has occurred. The explosions which took place when iodine was ignited in the presence of nitrous oxide were presumably due to the formation of the explosive compound, nitrogen tri-iodide, and this combination should be avoided. The explosions which occurred with nobecutane were probably caused by the contained propellants and it is clearly important to keep heat away from this substance and its successors. It is apparent from the experiments of diluting the alcohol in the antiseptics tested that any substance containing more than 10 per cent alcohol is potentially inflammable, and it is therefore recommended that whenever cautery or diathermy is to be used on or near the body surface, one of the many aqueousbased antiseptics is employed and the reduction in antiseptic efficacy (Lilley and Lowbury, 1971) be accepted, or if an alcohol-based antiseptic is used this should be cleaned off with a dry swab before the diathermy is used. Acknowledgements We wish to thank Mr S. Askill, Mr S. E. R. Mable and Mr J. Powell of the Anaesthetic Research Department, Royal College of Surgeons, for their help
in constructing the apparatus; the staff of the Wheatstone Physics Laboratory, King’s College, University of London, for their assistance in spot welding; Mr G . W. V. Stark of the Fire Research Station, Boreham Wood, for much helpful information; and Mrs Jill Taylor of the Norfolk and Norwich Institute of Medical Education, Norfolk and Norwich Hospital, for her secretarial work. References and INGRAM G. s. (1971) Flammability of drape materials in nitrous oxide and oxygen. Anaesthesia 26, 281-288. ELKINGTON A. (1971) Theatre fire. Br. Med. J . 2, 769. LILLEY H . A. and LOWBURY E. J. L. (1971) Disinfection of the skin: an assessment of some new preparations. Br. Med. J. 3, 674-676. MAGRUDER G . B. and GUBER D. (1970) Fire prevention during surgery. (Correspondence.) Arch. Ophthalmol. 84, 237. MEDICAL DEFENCE UNION (1956/7, 1961, 1971, and 1975) Annual Reports. London, Newnes. NEWNES G. (1952) Engineering Reference Book. London, Newnes, p. 1356. ZABETAKIS G. M. (1965) Flammability characteristics of gases and vapours. Bulletin 627 of the US Bureau of Mines. Washington, US Government Printing Office. CAMERON B. G. D.
983
Inflammable antiseptics and theatre fires C . E . B R I S C O E , D. W . H I L L A N D J . P . P A Y N E * SUMMARY
This paper describes an investigation designed to find out if theatre fires could be started by the antiseptic painted on the patient's skin being ignited by cautery or diathermy. It was found that hot wire cautery or diathermy generated enough heat to ignite all alcohol-based antiseptics even if these contained as little as 20 per cent alcohol. They could also cause iodine to explode in the presence of nitrous oxide, and nobecutane to explode in the presence of nitrous oxide or increased oxygen. The likelihood of these combinations causing fires is discussed, and it is recommended that when diathermy or cautery is to be used near the surface of the body, either an aqueous-based antiseptic is used or if spirit solutions are required they are carefully dried of before proceeding. THEoccurrence of minor fires around the bodies of patients during surgical procedures continues to be reported (Magruder and Guber, 1970; Elkington, 1971); and stories of unreported fires abound. These fires are often associated with the use of cautery or diathermy on the body surface. The possibility that these instruments might ignite the surgical drapes was investigated by Cameron and Ingram (1971), but the initial cause of such fires may be ignition of the antiseptic painted on the patient's skin which subsequently ignited the drapes. An experiment was therefore designed to mimic the conditions under which these fires occur. The temperature at which the commonly used antiseptics were ignited by a hot wire was investigated both in air and in an atmosphere of anaesthetic gases such as might be encountered when the patient's expiratory valve lies close to the operation site. These temperatures were then compared with those encountered in clinical practice.
Materials and methods A brass fire box (5 cm diameter) was constructed with an electrically heated nichrome wire spiral built into it. This wire was connected to a variable resistance enabling the temperature to be varied from room temperature to over 1200 "C. A chromel-alumel thermocouple was spot-welded on to the surface of the wire and connected to a voltmeter reading in mV. The temperature at the surface of the wire was then obtained from reference tables and the figures were checked on an optical pyrometer. In order to introduce various gas mixtures, one end of the fire box was connected to a gas supply from an anaesthetic machine while the other end was open, allowing the gas to flow across the hot wire. The gas
passed through a water trap to avoid a flashback explosion and the oxygen concentration was measured in a Servomex oxygen analyser. The antiseptics and materials to be tested were introduced on a copper saucer of 1.3cm diameter with a long handle, and the surface of the liquid or solid material was placed as close to the rod as possible without touching it. The rod was then maintained at increasing temperatures for 30 seconds at a time until ignition occurred. The time to ignition and the ignition temperature were first recorded in air, and then in varying mixtures of nitrous oxide and oxygen, ending with 100 per cent oxygen. Several of the antiseptics tested were in a 70 per cent alcohol mixture and the effect on the ignition temperature of diluting the alcohol was investigated. The possibility that the ignition point might be influenced by a patient's expiratory valve blowing on the substance was examined by increasing the gas flow through the fire box.
Results Table I shows the temperatures of the wire required to ignite the substances tested, first in air, then in 30 per cent oxygen and 70 per cent nitrous oxide, and finally in 100 per cent oxygen. The antiseptics based on 70 per cent industrial alcohol ignited at around 900 "C, but up to 90 "C lower than this in the nitrous oxide/ oxygen mixture and a few degrees lower still in 100 per cent oxygen. The antiseptics in aqueous solution would do no more than smoulder without supporting a flame and they only did this at temperatures of lo00 "C or over. Two substances exploded. One was iodine at 820 "C in the presence of nitrous oxide, and the other was nobecutane in both the nitrous oxide/oxygen mixture and in 100 per cent oxygen at 820 and 790°C respectively. The temperatures at which the surgical drapes, sterile paper, green towels and gauze ignited are also shown. These are all lower than for the fluids, lying between 730 and 770 "C, and showed a marked drop in the presence of nitrous oxide and oxygen to below 500 "C. Soaking these materials in the ignitable antiseptics resulted in their ignition temperatures rising to nearer the ignition temperatures of the fluids. The length of time before ignition proved not to be an important consideration. All the substances ignited within 15 seconds if they were going to ignite and if
* Anaesthetic Research Department, Royal College of Surgeons, London. Present address of C. E. Briscoe: Norfolk and Norwich Hospital, St Stephen's Road, Norwich. 981
C. E. Briscoe et al. Table I: TEMPERATURE OF IGNITION OF VARIOUS ANTISEPTICS
In air
Substance
Chlorhexidine and cetrimide in 70% alcohol (Savlon) 915 Chlorhexidine digluconate in 70% alcohol (Hibitane) 920 Iodine in 70% alcohol 930 Proflavine in 70% alcohol 890 Thiomersal in 50% alcohol (Merthiolate) 920 Chlorhexidine digluconate in aqueous solution (Hibitane) No ignition Chloroxylenol in aqueous solution (Dettol) N o ignition Povidone-iodine in aqueous solution (Disadine, Betadine or Pevidine) No ignition 890 Nobecutane Gauze Green towels Sterile uauer
780 770 720
Table 11: TEMPERATURE OF IGNITION OF VARYING DILUTIONS OF CHLORHEXIDINE AND CETRIMIDE IN ALCOHOL Ignition temperature ("C) In 30% oxygen/ Alcohol W ) In air 70% nitrous oxide In 100% 0. 825 70 870 870 60 50 40 30 20 10
880 890 880
940*
870 870 870 870 940 990*
850 850 850 870 890
*
* Flame not supported. Table 111: EFFECT OF GAS FLOW ON IGNITION TEMPERATURE OF CHLORHEXIDINE AND CETRIMIDE IN 70 PER CENT ALCOHOL Flow of air: No flow Ignition temperature ("C): 1 litre/min 2 litres/min 4 litreshin
890 890 920 930
the temperature was then raised 20 "C they could be guaranteed to ignite within 3 seconds. An attempt was made to ascertain how much dilution of the alcoholic antiseptics would be needed to prevent them igniting and the results are shown in Table II. In fact, flames were supported at all dilutions down to 20 per cent alcohol if nitrous oxide and oxygen were present, although the ignition temperatures were a little higher at these dilutions. Table 111 shows the effect of increasing the gas flow through the fire box. Raising the gas flow from zero to 4 litres/min resulted in the temperature of the wire having to be raised 40 "C to ignite the same material. Discussion Fires are a very alarming and unexpected complication of a surgical procedure. A number of these fires occur when non-inflammable anaesthetic gases are in use, and they often happen when diathermy or hot cautery is being applied to, or near, the surface of the body. Cameron and Ingram (1971) demonstrated that the surgical drapes could be ignited by a hot wire cautery, but these are usually removed from the site of surgery and the fires may well be initiated by the vapour from antiseptic catching fire. The heat of the skin will 982
Ignition temperature ("C) In 30% oxygen/ 70X nitrous oxide In 100% 0, 870 840 820 (explodes) 880 890
N o ignition 970 (smoulders) I100 (smoulders) 820 (explodes) 485 485 520
825 820 820 870 890
N o ignition 970 (smoulders) I 1 0 0 (smoulders) 790 (explodes) 460 460 490
ensure that this is in high concentration near the operation site. Thus, a fire known to one of the authors occurred after a surgeon painted the abdomen with chlorhexidine digluconate, opened the skin with a knife and then started to cut deeper layers with the diathermy. Another broke out while perineal warts were being cauterized after painting with a spirit solution. The two fires reported during ophthalmic operations (Magruder and Guber, 1970; Elkington, 1971) make no reference to the surgical painting, but they may also have been triggered in this way. Five cases reported by the Medical Defence Union (1956/7, 1961, 1971, 1975) were definitely ascribed to this cause. That fires could develop in this way is demonstrated by the results obtained in this paper. The ignition temperatures for these fluids of 800-900°C are the temperatures that would be obtained by a cautery glowing a cherry red colour (Newnes, 1972). Various manufacturers were in fact asked to state what temperatures their hot wire cautery could reach, but none was prepared to state a temperature as they said there were too many variables such as age and state of the rod or wire in use. There is, therefore, n o way of guaranteeing that a cautery will not reach the above temperatures, and the temperatures obtained by a diathermy arc are, of course, much higher. The temperatures measured in these experiments are considerably higher than the conventionally measured ignition temperatures. For instance, the ignition temperature of industrial methylated spirit in air is reported as 365 "C and cotton as 254°C (Zabetakis, 1965), but these are measured by raising the temperature of the whole substance until spontaneous ignition occurs. A different set of circumstances arises when substances are exposed to a spark or hot wire. In this case, which is the clinical situation, the temperature source is small and the ignitable material comparatively large. Conduction and convection can then reduce the amount of material exposed to the temperature to amounts that prevent the oxidative reactions of combustion taking place, unless the source temperature is considerably higher than that of a complete environment that would bring about ignition. Wind increases the convection and, as the results demonstrate, raises the ignition temperature.
Inllammable antiseptics and theatre 6res An atmosphere of nitrous oxide or oxygen slightly decreases the ignition temperature but greatly increases the rate of burning and heat of combustion once ignition has occurred. The explosions which took place when iodine was ignited in the presence of nitrous oxide were presumably due to the formation of the explosive compound, nitrogen tri-iodide, and this combination should be avoided. The explosions which occurred with nobecutane were probably caused by the contained propellants and it is clearly important to keep heat away from this substance and its successors. It is apparent from the experiments of diluting the alcohol in the antiseptics tested that any substance containing more than 10 per cent alcohol is potentially inflammable, and it is therefore recommended that whenever cautery or diathermy is to be used on or near the body surface, one of the many aqueousbased antiseptics is employed and the reduction in antiseptic efficacy (Lilley and Lowbury, 1971) be accepted, or if an alcohol-based antiseptic is used this should be cleaned off with a dry swab before the diathermy is used. Acknowledgements We wish to thank Mr S. Askill, Mr S. E. R. Mable and Mr J. Powell of the Anaesthetic Research Department, Royal College of Surgeons, for their help
in constructing the apparatus; the staff of the Wheatstone Physics Laboratory, King’s College, University of London, for their assistance in spot welding; Mr G . W. V. Stark of the Fire Research Station, Boreham Wood, for much helpful information; and Mrs Jill Taylor of the Norfolk and Norwich Institute of Medical Education, Norfolk and Norwich Hospital, for her secretarial work. References and INGRAM G. s. (1971) Flammability of drape materials in nitrous oxide and oxygen. Anaesthesia 26, 281-288. ELKINGTON A. (1971) Theatre fire. Br. Med. J . 2, 769. LILLEY H . A. and LOWBURY E. J. L. (1971) Disinfection of the skin: an assessment of some new preparations. Br. Med. J. 3, 674-676. MAGRUDER G . B. and GUBER D. (1970) Fire prevention during surgery. (Correspondence.) Arch. Ophthalmol. 84, 237. MEDICAL DEFENCE UNION (1956/7, 1961, 1971, and 1975) Annual Reports. London, Newnes. NEWNES G. (1952) Engineering Reference Book. London, Newnes, p. 1356. ZABETAKIS G. M. (1965) Flammability characteristics of gases and vapours. Bulletin 627 of the US Bureau of Mines. Washington, US Government Printing Office. CAMERON B. G. D.
983
