Fires and
Explosions In OR
and ICU
By
Professor Dr. Mohammed Saeed Abd El Aziz
• General principles
• Combustible agent or fuel + O₂ or oxidizing agent
→ reaction products + energy.
• Activation energy
• Heat energy → ↑ temp. of the mixture which when
exceed certain level → self sustained
• 2 C₃ H₆ + 9 O₂ → 6 CO₂ + 6 H₂O+ Energy
• Cyclopropane to O₂ 18% or 2:9 →
Stoichiometric concentration.
• 2 Vols + 9 Vols → 11 Vols
• It is the concentration at which all the combustible vapor and
oxidizing agent are completely used up → Stoichiometric
concentration.
• Stoichiometric mixtures→ the most suitable mixture for
ignition.
• Different mixtures → less violent reaction or no ignition.
• Flammability limit is the limit outside which the mixture will
not burn.
• Cyclopropane
• Lower flammability limit
limit
2.5%
upper flammability
2:9
18%
63%
In O₂
2.5%
4.3%
100%
In air
Lower flammability limit
upper flammability limit
limit
stoichiometric
limit
concentration
No ignition
Fire
Explosion
Fire
No ignition
Fire
Explosion
• Speed
low
high
• Pressure
1 bar
25 bar
•
•
•
•
Temp.
200-500 C⁰
3000 C
Light
Less
More
Sound waves
minimal
maximal
In normal anesthetic practice, cyclopropane burns but not
explodes in air.
• Flammability range is reduced and stoichiometric conc. Is
altered.
• The inert nitrogen molecules absorb energy+ does not take
part in the reaction; reaction is less violent.
• 2C₃ H₆+ 9O₂ +36 N₂→ 6 CO₂ + 6 H₂O+ 36 N₂ + Energy
_________
9( O₂ + 4 N₂ )
Nitrous oxide is an oxidizing agent, rapidly breaks down in the
presence of heat of fire or explosion to release O₂→33 % O₂
mixture→ more energy
2 N₂O = 2 N₂ + O₂ +Energy ie, more violent reaction in the
presence of N₂O and release more energy.
• Other Flammable Agent
• Ether
Lower flammability limit
limit
upper flammability
Stoichiometric conc.
2%
14%
82%
100%
in O₂
2%
34%
100%
in air
Ether does not explode in air but burns.
The conc. Of ether in oxygen used in anesthesia→ within limits for
explosion.
• If liquid ether split→ high conc. Of ether vapour near the
floor→ approach high flammability limit in air → burn→ cool
flames, it is invisible and at lower temp. level.
• Ether→ CO₂ + H₂ O , this in normal reaction, but in
• Cool flames → oxidation is partial→ acetic acid and
acetaldehyde.
• Cool flames→ transmit risk of ignition to anesthetic circuit
(breathing system)
• Flame : is a combustion associated with emission of light and
heat , a- static (confined) b- self- propagated.
• The Fire Triad a-Fuel b- a source of ignition or heat. C- an oxidizer
• Other Flammable Agents (Fuel)
•
•
•
•
Ethyl Chloride
Ethylene
Vinyl ether, they are less commonly used.
Halothane and trichloroethylene → suitable mixture and
suitable temp.→ ignition but not in concentration used in
anesthetic practice.
• Anesthetic agents now are not flammable but other
agent, like ethyl alcohol, are flammable.
• Saturated vapour of alcohol in air in normal room temp.
6% mixtures
•
Stoichiometric conc
0%
3%
6%
19%
alcohol in
↓
air
Fire risk of saturated vapour at room temp.
Surgical spirit
Methane- hydrogen in patient’s gut with diathermy→
fire.
Ethyl chloride→ anesthetic spray.
Paper, plastic drapes, dressings.
Pure O₂+ pressure +high speed → high fire and
explosion risk, oil and grease must be avoided in any
O₂ supply system.
• Activation Energy and Ignition
Temperature
• Combustible agent + O₂, they are apart by
repulsive forces and in order to burn molecules
should be close enough to react → ↑ the speed of
collision →↑ temp. by spark or some source of
heat ( enough heat to reach activation energy).
• Ignition temperature:- the temperature at which a
mixture must be raised for combustion to start.
• It varies with components and proportion of
potentially explosive mixture.
• Stoichiometric conc. Of many explosive mixture temperature is
about 400 C⁰ but ether-O₂ mixture is low as 150 C⁰ .
• Spirit lamb, diathermy, Lasers→ ignite flammable materials.
• Sparks→ activation energy→ activate an ether O₂ explosion
when present in stoichiometric conc. (spark is around 1
microjoule in value but it has a high voltage , it is more risky
than hot wire or open flame)
• Static Electricity
• Important source of sparks
• Conductive floor, low resistance → ↑ electric risk , high
resistance↑ build up of static electricity.
• Antistatic rubber. Soled shoes contain carbon.
• ETT conduction by humidified gases passing through
it.
Equipments→ sparks or static electricity.
2 types of flammable mixtures
-mixtures with oxygen or nitrous oxide as
oxidizing agent.
-mixtures with air, activation energy is less in
the first one.
Flammable mixtures near anesthetic machines
5cm-25cm.
Category of equipment →APG (avoid ignition with O₂ or
nitrous oxide- green band)
green circle)
AP (avoid ignition with air-
Types of operating room fires
A -Fires in the patient
1- Laser
a- upper airway surgery b- lower airway surgery
2-Electrocautry a- during tonsillectomy b- during
laparoscopic surgery c- during tracheostomy.
B- Fires on (outside) the patient
1- During monitored anesthesia care(MAC) for head and
neck surgery
2- During skin preparation using isopropyl alcohol.
• Safety precaution to prevent fires and explosions
• 1- Avoidance of the use of flammable anesthetic
agents ( C-F bond) decrease flammability.
• The use of sources of ignition such as diathermy or laser
under controlled conditions.
• Use the Iow-flow or closed circuits.
• Allow good ventilation of OR.
• Use a well functioning scavenging system.
• 2-Classification of equipments according to the
zones of risk: 5 cm zone (anesthetic mixtures is high and
oxidizing agent O2 or N2O), 25 cm zone (anesthetic mixtures is low and
oxidizing agent is air), APG( 5cm) and AP (25 cm) equipment
• 3-Prevention of electric sparks
• PPM (periodic preventive maintenance)
• Spark –proof mercury switches.
• Dry battery.
• 4-Prevention of static electricity (antistatic materials)
• Antistatic floors, antistatic breathing circuits, antistatic cloths,
antistatic wheels, antistatic rubber-soled shoes, relative humidity
less than 50% and grounding or earthing.
• 5-Fire-fighting equipments (fire extinguishers)
• Should be available all the time, class A –B- C e g, Halon fire
extinguisher, CO2 extinguishers and pressurized water.
• 6- Precaution during laser surgeries.
• Extinguishing a fire
•
•
•
•
•
1-Remove oxidizing agents.
2-Remove burning drapes.
3-Use a fire blanket.
4-Sprinkler system.
5-Halton fire extinguishers are used.
Thank you