Fire fighters involved in search and rescue operations occasionally use SCUBA (Self-Contained Underwater Breathing Apparatus) and other underwater breathing systems in the line of duty. Use of these systems in the underwater environment may present a number of unique occupational exposures with potential medical implications. A full understanding of these exposures and their potential medical consequences will allow the diver to train, plan, and work in a manner which minimizes the potential for work related diving injury.

The following, although by no means a complete discussion of diving medicine, will provide the following information:

  1. A brief overview of the history of diving.
  2. An outline of basic diving physics and effects of diving on the body.
  3. A review of the major medical complications of diving including:
    • Barotrauma
    • Pulmonary Over-Inflation Syndrome (POIS)
    • Decompression Sickness
    • Nitrogen Narcosis
  4. A discussion of diving fitness for duty criteria.
  5. Discussion of diving safety = training + planning.
    • Diving Safety and Planning Checklist
    • Diving Emergency Assistance Checklist
  6. Links for answers to more complex diving medicine questions.


The IAFF does not endorse any medications, product, or treatment described, mentioned or discussed in any of the services, databases, or pages accessible within or on this site. Furthermore, the IAFF makes no representations concerning the efficacy, appropriateness, or suitability of any such products or treatments. In view of the possibility of human error or advances in medical knowledge, neither the IAFF, its staff, nor any other party involved in providing the services, databases, or pages accessible within or from this site warrant that the information contained therein is in every respect accurate or complete and they are not responsible nor liable for any errors or omissions that may be found in such information or for the results obtained from the use of such information. You are encouraged to consult other sources and confirm the information contained in any of the services, databases, or pages accessible within or on this site. If erroneous or otherwise inaccurate information is brought to our attention, a reasonable effort will be made to correct or delete it. Such problems should immediately be reported to the IAFF – Health and Safety Department.

(excerpts from Bove’s Diving Medicine, 3rd edition)

Diving has been used as a means of underwater work and exploration for thousands of years likely originating with the use of breath-hold diving in pursuit of shells, pearls, and lost tools. Many commercial breath-hold divers in the commercial pearl/shell industries regularly “free dive” to depths of 60-80 feet, with world records held in excess of 400 feet.

Use of modern diving bells extended working time by trapping air in an inverted container while workers operated inside. Diving bell activity is reported as early as 332 BC, when Alexander the Great deployed military divers from diving bells for enemy vessel destruction at the Siege of Tyre.

Later, the innovation of surface supplied diving allowed workers to operate on the ocean floor free of constraint, first reported by August Siebe in 1819. This technology evolved into the classic “deep-sea” diving suits used by the US Navy including the Mark V diving suit, used by the Navy until 1982.

During the WWII era, two major diving advances occurred which dramatically altered diving technology. The first, Jack Browne’s triangular diving mask, was widely used by divers engaged in commercial activities. The second, the 1943 invention of self-contained underwater breathing apparatus (SCUBA) and the demand regulator by Cousteau and Gagnon, caused the growth of sport diving and allowed the use of diving in civilian applications. Although a variety of underwater breathing systems are available in the commercial marketplace, content of this site will focus primarily on open circuit scuba systems, the breathing apparatus most likely to be used by fire fighters and other public safety divers.

An understanding of dive medicine first requires an understanding of the physics, barometric (pressure) changes, and gas effects caused by descent of the diver in the water column.

At sea level, atmospheric pressure exerts approximately 760mm Hg (1 ATM or 14.7 psi) on the human body. During a diver’s descent in the water column, pressure increases linearly at a rate of an additional 760 mm Hg (1 ATM) for every 33 feet of descent in sea water (34 feet in fresh water). A diver descending to 99 feet would therefore be exposed to a total of 4 ATM [1 ATM + (99ft/33)] or 4 times as much pressure as experienced on the surface. Pressure and pressure gradients have a number of potential effects on the diver including: barotrauma, pulmonary over-inflation/air-gas embolism secondary to uncontrolled ascent, increased “on-gassing” of nitrogen creating the potential for decompression sickness upon return to the surface, and nitrogen narcosis caused by the “intoxicating” effect of elevated nitrogen levels at depth.

The relationship between pressure and volume is best described by Boyle’s Law which states: given any constant temperature, pressure and volume are inversely related according to the equation P1V1 = P2V2. It is easiest to imagine this relationship as illustrated below.

If a garbage bag were filled with 1 liter of air and then taken from the surface to 33 feet of depth, the air would occupy only half it’s original volume (The pressure has doubled). Similarly, a diver on SCUBA making an uncontrolled ascent from 33 feet without exhaling, would double the volume of air in his lungs, potentially causing pulmonary over-inflation and an air-gas embolism.

A second concept essential to understanding diving medicine is the relationship between gas partial pressure and the ability of a gas to dissolve in a solute. Henry’s Law states that the amount of gas which will dissolve in a liquid at any given temperature is a function of: 1) the partial pressure of the gas in contact with the liquid, and 2) the solubility coefficient of the gas in the liquid. As a diver descends in the water column and pressure increases, blood nitrogen levels gradually rise as more nitrogen is dissolved in the blood. These elevated nitrogen levels, at depths greater than 100 feet, may cause an intoxicating effect known as nitrogen narcosis. Although initially limited to dissolution in the bloodstream, the nitrogen load is gradually absorbed by other body compartments. Upon return to the surface, as pressure decreases, this nitrogen may come out of “solution” and cause decompression sickness if the diver has exceeded no-decompression limits.

An example of this concept is a shaken carbonated beverage can. While pressurized, the carbon dioxide remains in solution in the beverage. However, if the can is opened and the is pressure removed, the carbon dioxide is no longer soluble under the reduced pressure and comes out of solution. Decompression sickness occurs in a similar manner only reducing the pressure allows nitrogen instead of carbon dioxide to escape for the body.


Barotrauma refers to trauma or damage caused to body tissues by the mechanical effects of a pressure differential (between a body cavity and the hydrostatic pressure surrounding the body). For barotrauma to occur in a body area, the following five conditions must be met.

i) There must be a gas filled space

ii) The space must have rigid walls

iii) The space must be enclosed

iv) The space must have vascular penetration

v) A change in ambient pressure must occur.

A diver descending in the water column must “equalize” to prevent a middle ear squeeze from occurring as the outside pressure exceeds that inside the middle ear. This scenario commonly occurs in the context of eustachian tube dysfunction (due to anatomy or congestion) or secondary to inadequate equalization during descent. If pressure continues to increase without equalization, the ear drum will eventually burst as the pressure differential increases.

Barotrauma is must frequently seen during descent in the water column (referred to as a “squeeze”), but may also occur during ascent (“reverse squeeze”). Middle ear squeeze is the most common form of barotrauma; however, other types of barotrauma include: sinus, external ear, thoracic, face mask, gastrointestinal, and tooth squeezes.

Prevention: Proper equalization during diving prevents most sinus and ear squeeze from occurring. Given this fact, diving should not be attempted if the diver is unable to clear secondary to congestion. If decongestants are used, avoid those with a narcotic or sedative effect.

Treatment: To treat squeeze during descent: Stop descent. If efforts to equalize fail, ascend a few feet, and avoid clearing during ascent or forceful valsalva. If further efforts to equalize pressure fail – abort the dive. If the diver reports dizziness, abort the dive, and evaluate need to launch the stand-by diver. Follow-up with personnel trained in diving medicine.

To treat a reverse squeeze during ascent: Stop ascent and if clearing does not occur, descend 3 feet. Ascend slowly. Avoid forceful valsalva. Evaluate need to launch stand-by diver. Follow-up with personnel trained in diving medicine.

Pulmonary Overinflation Syndromes (POIS)

Pulmonary over-inflation syndromes are a group of disorders caused by over expansion of the lung. These syndromes generally occur secondary to ascent without exhaling. This group of disorders includes: pneumothorax, mediastinal emphysema, subcutaneous emphysema, and air gas embolism.

Pulmonary overinflation is most commonly seen in the context of inadvertant breatholding during an uncontrolled ascent by an inexperienced or poorly trained diver. Following Boyles Law, the air volume of a diver who has taken a breath at depth exceeds the divers lung capacity causing overpressurization. As little as a 90 cm H2O overpressurization may cause the alveoli in the lung to rupture, potentially allowing release of air into body spaces including the mediastinum, the neck, the chest cavity, or the pulmonary vasculature (discussed below).

Overinflation is most likely to occur near the surface as the greatest pressure and volume changes occur in this zone. Constant exhalation is therefore necessary any time a diver is surfacing, as failure to exhale may result in overinflation and consequent alveolar rupture.

Pneumothorax – is caused by air outside the lung that is trapped in the chest cavity

Mediastinal and Subcutaneous Emphysema – are caused by air which is trapped behind the breast bone in the mediastinaum (mediastinal emphysema), or air which has dissected into the neck (subcutaneous emphysema)

Air Gas Embolism – is caused by air which has entered the pulmonary capillaries (lung blood vessels) and enters the left side of the heart. After leaving the left ventricle, these air bubbles may either travel to the coronary arteries (heart blood vessels), or the cerebral arteries which may cause symptoms similar in many respects to a heart attack or stroke. The diagram below illustrates this process.

Symptoms: Symptoms associated with pulmonary overinflation syndromes range from shortness of breath seen with pneumothorax, to changes in voice and substernal air trapping seen with mediastinal and subcutaneous emphysema, to air gas embolism symptoms which may include mental status changes and loss of consciousness.

Any time a diver losing consciousness within 10 minutes of surfacing or upon surfacing, should be assumed to have an air gas embolism until proven otherwise. Symptoms generally occur within minutes of an uncontrolled ascent, and should be referred to a medical professional immediately.

Prevention: Prevention of pulmonary over-inflation syndrome should first focus on a medical selection process eliminating those with evidence of active lung disease or a history of spontaneous pneumothorax. Those with respiratory disease including (but not limited to) asthma, lung surgery, and traumatic pneumothorax should undergo a full medical examination before diving. Second, training in diving physics/physiology and correct use of diving equipment is essential. Third, An emergency contigency plan should exist for treatment of diving injuries including: location and contact numbers for the nearest recompression facility (contact DAN for recognized chambers).

Treatment: Treatment of pulmonary overinflation syndromes differs according to severity of symptoms, but whenever suspected should be referred to a medical professional familiar with diving medicine.

Pneumothorax – a mild pneumothorax may be treated with 100% oxygen by face mask, however, more severe cases may require placement of a chest tube, a procedure which should only be performed by experienced medical personnel. A pneumothorax seen in combination with suspected air gas embolism should not prevent emergent recompression.

Mediastinal and Subcutaneous Emphysema – minor mediastinal or subcutaneous emphysema treatment may be accomplished through 100% oxygen therapy; however, more severe cases may require recompression therapy. The injured diver should be immediately transfered to an emergency room facility for evaluation by a medical professional familiar with diving medicine. Chest xrays should be taken to rule out pneumothorax.

Air Gas Embolism – divers suffering from air gas embolism may require immediate basic life support/CPR upon surfacing so remember your ABC’s (Airway, Breathing, Circulation). Be sure the diver has a patent airway (free of vomit, debris), check breathing and circulation, and begin CPR if indicated. Alert the emergency transport team immediately and alert the receiving medical/recompression center so recompression therapy may be utilized as early as possible.

If 100 percent oxygen is available, it should be administered by face mask. Oxygen should only be discontinued if convulsions consistent with oxygen related seizure occur. Cover the diver with blankets and transport the patient to the nearest emergency room in preparation for transfer to the nearest recompression chamber. In route monitor for and treat cardiac dysrhythmias per ACLS protocals. Hydration is recommended when possible.

Decompression Sickness

Decompression sickness or “the bends” was first reported by Sir Robert Boyle in 1670 during animal pressure experimentation when Boyle reported, “… a viper furiously tortured in our exhausted receiver…that had manifestly a conspicuous bubble moving to and fro in the waterish humour of one of his eyes.” The pressure related disease acquired it’s nickname “the bends” after workers emerging from pressurized construction on the Brooklyn Bridge adopted a posture similar to fashionable ladies of the period (“the Grecian Bend” – below) because of symptoms of decompression sickness.

As a diver descends in the water column, the combination of increased pressure (Boyles Law) and consequent increased solubility of nitrogen in the body’s tissues (Henry’s Law) causes an increase in the “on-gassing” of nitrogen. Air is made up of approximately 79 percent nitrogen, which on the surface, is easily cleared from the body. However, as the diver goes deeper, the pressure increases, increasing the partial pressure of nitrogen, and the “on-gassing” of nitrogen exceeds the body’s ability to clear the gas. The deeper the diver goes, the faster this process occurs. A diver with a “nitrogen burden”, upon surfacing may allow nitrogen inside the body to come out of saturation (similar to removing the lid from a shaken/pressurized cola can) causing bubble formation. These bubbles may cause joint pain, sensory changes, limb weakness, and in severe cases paralysis and death, the symptoms being dependent upon location of bubble formation (joints, spinal nerves, spinal cord, etc.). This process is known as decompression sickness, or “the bends”. Onset of these symptoms generally occurs within 12 hours of surfacing from a dive (90% within 6 hours), however, a physician familiar with diving should be consulted anytime decompression sickness is a potential diagnosis.

History: Nitrogen burden and onset of symptoms within 12 hours of surfacing (90% within 6 hours)

DCS Type 1
Pain – Periarticular (joint)

Mottling of the skin (cutis marmarota) – shown below

Swelling (lymphatic)
DCS Type 2
Pulmonary – cough, “chokes”

Spinal – sensory change, weakness

Inner ear – ringing, hearing change

Cerebral – mental status changes

Prevention: Decompression sickness may be prevented by following these basic steps: 1) Plan the dive prior to entering the water and stick to it. 2) Strictly adhere to no-decompression (No-D) limits as listed in available commercial dive tables. 3) Dive team members should be held to physical fitness standards. Adipose tissue (fat) readily absorbs nitrogen, increasing the potential for decompression sickness. 4) Train for diving often. When adverse conditions do occur, as is common in diving, the diver and the diving supervisor must know how to deal with the situation. 5) An emergency contigency plan should exist for treatment of diving injuries including: location and contact numbers for the nearest recompression facility (contact DAN for recognized chambers). 100% oxygen for treatment until recompression.

Treatment: Immediate transfer to a recompression chamber for evaluation by a physician familiar with diving medicine. In route, oral or iv hydration is recommended. If available, 100% oxygen should be administered by face mask.

Nitrogen Narcosis

As mentioned above, increases in pressure will increase body nitrogen saturation causing a progressive “intoxicating” nitrogen effect generally seen in divers at depths in excess of 100 feet. This effect is highly variable between individuals, but many divers refer to “the martini rule” which suggests that every 50 feet of sea water descended in excess of 100 feet has the effect of drinking a martini on an empty stomach. Most divers report symptoms similar to alcohol intoxication including decreased reasoning ability, increased reaction times, lightheadedness, and euphoria. Disorientation and poor judgement may result, placing the diver at risk in the unforgiving underwater environment.

Nitrogen narcosis generally resolves with ascent from depth and acclimatization may occur in divers with a history of exposure. Alternative breathing mixtures should be considered if nitrogen narcosis is regularly reported as symptoms may effect diving safety.

The underwater environment presents a number of unique stressors which require that divers maintain a reasonable level of physical/physiological psychological fitness while acting as public safety divers. Difficulties encountered in the underwater environment include:

-Heat loss due to exposure to water likely to be below the core body temperature

-Physical demands of propulsion in the underwater environment (cardiovascular, pulmonary, etc.)

-Respiratory demands of breathed compressed gas, etc.

These and other physiologic demands of diving require the diver to maintain a sound level of fitness and be comfortable underwater as lack of fitness, and lack of diving proficiency may both have severe consequences in the unforgiving underwater environment.

A listing of fitness for duty suggestions may be found at the attached link, Diving Medicine Online. Those with questions specific to cardiovascular disease might also try Bove’s Although these sites give excellent fitness for duty outlines, medical conditions vary by individual and should be reviewed by a medical professional familiar with diving medicine before beginning a diving regimen. Personnel involved in diving should also discuss their job responsibilities with their primary care physician during their annual physical exam.

The US military has for years performed diving operations in hazardous environments while maintaining a solid safety record, minimizing risk to divers. These safety records are the result of planning, training, and exhaustive preparation before each dive. Similar to military diving, fire fighters involved in search and rescue operations are required to operate in less than optimal diving conditions and may be forced to make difficult decisions in an environment which, like firefighting, is inherently unforgiving.

A critical element of any diving operation is an emergency planning checklist which should include use of a diving safety and planning checklist and an emergency assistance checklist. Both these may be found below.

Diving Safety and Planning Checklist


Detailed advanced planning is the foundation of diving safety


  • Ensure the mission objective is clearly defined
  • Determine that non-diving means of mission accomplishment have been considered and eliminated as appropriate
  • Coordinate emergency assistance
  • Review relevant operational instructions


  • Natural Hazards

1. Atmospheric:
__ Exposure of personnel to extreme conditions (temperature/wind)
__ Adverse exposure of equipment and supplies to elements
__ Delays or disruption caused by weather

2. Surface
__ Sea sickness
__ Water entry and exit
__ Handling of heavy equipment in rough seas
__ Maintaining location in tides and currents
__ Ice, flotsam, kelp, and petroleum in the water
__ Delays or disruption caused by sea state

3. Underwater and Bottom:
__ Depth which exceeds diving limits or available equipment
__ Exposure to col temperature
__ Dangerous marine life
__ Tides and currents
__ Limited visibility

  • On-site Hazards:

__ Local marine traffic and other operations
__ High powered active sonar
__ Radiation contamination and other pollution (chemical, sewer outfalls, etc.)

  • Mission hazards:

__ Decompression sickness
__ Communication problems
__ Drowning
__ Other trauma

  • Objective hazards:

__ Entrapment/entanglement
__ Shifting or working of object


  • Diving Personnel:

1. Assign a complete and properly qualified Diving Team
2. Assign the right man to the job
3. Verify that each member of the diving team is properly trained and qualified for the equipment and depths involved.
4. Determine that each man is physically fit to dive, paying attention to:
__general condition and any evidence of fatigue
__record of last medical exam
__ear and sinuses
__severe cold or flu
__use of stimulants or intoxicants

5. Observe divers for emotional readiness to dive:
__motivation and professional attitude
__stability (no noticeably unusual or erratic behavior)

  • Diving Equipment:

1. Verify that diving gear chosen and diving techniques are adequate and authorized for mission and particular task.
2. Verify that equipment and diving technique are appropriate for the depth involved
3. Verify that life support equipment has been tested and approved
4. Determine that all necessary support equipment and tools are readily available and are appropriate for the mission.
5. Determine that all related support equipment including winches, boats, cranes, floats, etc. are operable, safe, and controlled by professionals.
6. Check that all diving equipment has been properly maintained (with appropriate records) and is in full operating condition.

  • Provide for Emergency Equipment:

1. Obtain suitable communications equipment with sufficient capability to reach outside help; check all systems for proper operation.
2. Verify that a recompression chamber is ready for use and available within the required timeframe. Have emergency numbers on-hand.
3. Verify that a stocked first aid kit is available
4. If oxygen is being used for stand-by first aid, be sure the tank is full, properly pressurized, and that masks, valves, and accessories are fully accessible.
5. If a resuscitator will be used, check apparatus for function.
6. Verify that emergency transportation is either standing by or on immediate call.

  • Establish Emergency Procedures:

1. Know how to obtain medical assistance immediately
2. For each potential emergency situation, assign specific tasks to the diving team and support personnel.
3. Complete and post the Emergency Assistance Checklist; ensure that all personnel are familiar with it.
4. Verify that up-to-date copies of decompression tables are available.
5. Ensure that all divers, boat crews, and other support personnel understand diver hand and line pull signals.
6. Predetermine distress signals and call-signs.
7. Ensure that divers have removed anything from their mouths which could cause choking during the dive (gum, dentures, tobacco).
8. Thoroughly drill all personnel on emergency procedures giving attention to cross-training. Drills should include: Emergency recompression, fire, rapid dressing. restoration of breathing, eletric shock, entrapment, rapid undressing, first aid, embolism, near-drowning, uncontrolled ascent (blow-up), lost diver.


  • Complete Planning, Organization, and Coordination Activities:

1. Ensure contingency planning has been conducted.
2. Develop a flexible operational plan (Dive Plan) and state goals and tasks of each mission.
3. Completely brief dive team and support personnel as appropriate.
4. Designate a qualified diving supervisor to be in charge of the mission.
5. Designate a recorder/timekeeper and verify that he/she understands these duties.
6. Determine exact depth at the job site using a pneumfathometer or commercial depth sounder.
7. Verify existence of adequate compressed air for all planned operations, plus an adequate reserve for emergencies.
8. Ensure that no operations take place without the direct knowledge of the diving supervisor.
9. All efforts should be made to minimize bottom time. Water depth and diver condition should govern bottom time (not the amount of work needing done).
10. Ensure that when using SCUBA systems, a boat can be quickly cast off and moved to a diver in distress.

  • Perform Diving Safety Procedures, Establish Safety Measures:

1. Ensure each diver checks his/her own equipment in addition to checks made by tenders, technicians, and other support personnel.
2. Designate a stand by diver for all diving operations; the standby diver shall be dressed to the necessary level and be ready to enter the water if needed.
3. Assign buddy divers, when necessary, for all SCUBA operations.
4. Take precautions to prevent divers from being fouled on the bottom. If work is conducted inside a wreck or other structure, assign a team of divers to accomplish the task. One diver enters the wreck, the other tends his lines from the point of entry.
5. When using explosives, take measures to ensure that no charge will be fired while divers are in the water.
6. Brief all divers and support personnel on planned decompression schedules for each diver.
7. Verify that diving craft display proper signals, flags, and lights for diving operations in progress.
8. Ensure that protection against harmful marine life has been provided.
9. Verify that proper safety and operational equipment is aboard small diving boats/craft.

  • Notify Proper Parties That Diving Operations Are Ready to Commence including: the diving supervisor, ships bridge to ensure use of mechanical devices/propellers/thrusters/sonar/mooring systems does not occur, harbor master, coast guard (as required), recompression facilities, emergency transport teams.


Diving Supervisor ________________________________

Date ________________________________

Diving Emergency Assistance Checklist

Recompression Chamber


Name/Phone #

Diving Medicine Physician/Phone #

Response Time

Gas Supplies


Name/Phone #

Response Time


Air Transportation


Name/Phone #

Response Time



Name/Phone #

Response Time

Sea Transportation


Name/Phone #

Response Time

Fire Station


Name/Phone #

Response Time



Name/Phone #

Response Time


Related Links for Diving Medicine Questions

Diving Medicine Online