Potentially not one of the most exciting topics for discussion is fire and fire safety. However it is a necessary one and is presented today for those considering hyperbaric oxygen therapy. It’s also not intended to appear as any form of fear mongering or dramatic over representation of risk. It is intended to inform. We include extracts from the overview below which can be downloaded in full from the download and resource page.
Most units will conduct an induction along similar lines prior to commencing a treatment regime, and reputable units will have all the required and advised safety procedures in place. These should be obvious to see in the form of evacuation signs, fire suppression systems, written fire plans, pre-treatment briefings and such. Ordinarily patients attending a unit wouldn’t need to overly concern themselves with the compliance of the unit, since the staff are all usually highly trained in this regard and compliance is legislated, but casting an eye over these is always a good idea and seldom offends. Visible safety measures always sets minds at ease. The information presented here forms part of the informed consent process and it is important that chamber occupants adhere to certain safety guidelines.
We’ve mentioned before that we usually pressurise a chamber with air and not oxygen. The oxygen is delivered to the recipient by mask. The reason for this is to maintain an air atmosphere in the chamber for safety reasons. Most chambers are not designed for oxygen atmospheres. Maintaining an air atmosphere reduces the likelihood of a fire to levels commensurate with any other workplace. There is however potential for oxygen to leak from masks and collect, thus generating higher than normal concentrations in the chamber atmosphere or indeed in pockets.
Owing to these potentially higher concentrations of oxygen within a chamber, fire safety is a mandatory consideration. It is incidentally the one factor that chamber occupants have direct control over in the way of imported items. (BHA Guide to Fire Safety Standards for Hyperbaric Treatment Centres 1996)
High school physics teaches the fire triangle of which oxygen is an integral part. Oxygen itself is not flammable but it does support combustion vigorously when heat and fuel are present. Heat being an ignition source such as a spark or other localised hot spot. Removal of any one component of the triangle renders fire impossible. Since we cannot entirely remove oxygen, we take measures to remove fuel and ignition sources and sources of heat.
In atmospheres of above 24% oxygen, (remembering that normal atmospheric oxygen concentration is 20,9%), and under pressure, ignition temperatures of flammable materials are reduced, and in the presence of higher oxygen concentration, burn rates increase. For this reason we monitor concentration with equipment in the control panel and maintain oxygen concentration below 23% in the chamber by means of ventilating the chamber during treatments if required. This means we add air and release air at the same time to maintain pressure while changing the air in the chamber. It gets rid of smells too incidentally and stirs and cools the air. It is sometimes referred to as flushing. This is managed by the team operating the chamber from the control panel.
For this reason, all electronics in the chamber such as TV’s and communications units are low power 12 or 24-volt direct current (DC) units, and are designed for use in pressurised environments.
There is a wealth of information contained in the safety manuals published by the British Hyperbaric Association (BHA), on fire safety as well as general safety. Click through on the link to their publications page.
One example from their manuals is that at 6 atmospheres absolute, (6 ata or 50 meters of depth), paper will have an ignition temperature 25% lower than at normal pressure, and the burn rate will increase in the presence of elevated oxygen concentration. For this reason, it is advisable to limit excessive paper in the chamber. A book or magazine is fine though. Just not a whole library. As you can see, where risk exists and is mitigated, safety and a safe environment are ensured.
That said, at the pressures most HBOT and diving chambers operate at, this does not apply, and only represents an extreme scenario for academic purposes. It is unlikely a standard HBOT treatment will go anywhere near 6 ata with most treatments around 2 ata.
Ordinarily the only treatments or excursions reaching 6 ata, (50 meters), are ‘dry dives’ conducted as part of diver training and experience, and some US Navy air treatment tables which are so rarely used these days they are barely considered. Even preferred diving treatments for even commercial and military operations are limited to a maximum of 4 ata or more commonly 2,8 ata.
Obviously, anything containing any kind of solid, liquid or gaseous fuel is strictly prohibited, as these are considered ignition as well as fuel sources and are strictly prohibited in the chamber.
The chamber atmosphere can also become contaminated by certain materials which release vapour under pressure. Certain plastic, medications, and other materials vapour-off under pressure and are not allowed in the chamber. Substances containing oils such as face creams and cosmetics are also discouraged on the same basis as fuels. Hairspray too is forbidden.
Clothing and fabrics with low ignition temperature and high static spark probability are also excluded, such as nylon clothing. Cotton clothing is preferred with many chambers insisting on patients wearing pocket-less scrubs to avoid contamination and importation of dirt, oil and dust which can also be a problem as far as combustibility goes.
In many cases, it’s not so much the risk the item poses to the chamber or the occupants, but rather that the hyperbaric environment may also be harmful to the item. Items such as electronics with membrane switches and other sealed air spaces may crush under pressure, waterproof watches without gas release valves and even mobile phones can be affected.
Air is 800 times less dense than water. So even a waterproof item will allow the ingress of air, since it is only designed to resist water which has a far greater density. Over the duration of the treatment more air ingresses than can escape during de-pressurisation. As we understand from Boyle’s Law, gas compresses and re-expands according to the pressure being applied. If compressed air works its way into your mobile, or your watch, it can damage them when it expands. Or indeed if an air pocket inside a device shrinks, it can cause damage to the device if it cannot be equalised. Touch screens may also not work properly under pressure unless designed for use in a pressurised environment. They can activate multiple areas at once as can membrane switches. These items cannot be equalised, and unless designed to be pressure resistant, can implode. For these reasons, we exclude certain items from the chamber, which can be left at home or stored securely in the lockers provided, as listed below:
- Cigarette lighters
- Tobacco in any form, including chewing tobacco and Vapes
- Alcohol, including aftershaves
- Petroleum based chemicals, greases or fluids, including wheel chair/gurney wheel lubricant. Oxygen compatible lubricants must be used
- Drugs of any kind unless authorized by the Diving Superintendent and the nurse
- Large amounts of newspapers, books, magazines etc
- Non-fire-retardant bedding. Fire retardant bedding with a low static spark probability must be used
- Fountain pens and similar
- Electrical items which may implode, explode or have loose electrical connections, this includes mobile telephones
- Mercury thermometers
- Alcohol thermometers
- Nylon clothing
This list is not exhaustive or absolute, and different units will have different rules. In fact, phones are allowed in some units and my personal phone works just fine in the ‘pot’. It is at risk though of dysbaric damage caused by expanding or compressing air. Some units may disallow even more items, however this a good list to go on. As a patient, it isn’t worth trying to sneak something in. It’s a safety concern. No other reason. There is good reason these items are not allowed in the chamber. If in doubt, ask.
As mentioned this is not intended to cause undue stress or concern. your operators and attendants are highly trained and have a full and thorough understanding of the risks associated with hyperbaric compression. There are highly advanced fire suppression systems and deluge systems in place as well as specially designed fire extinguishers inside the chamber. there are also usually stringent evacuation protocols in place. Your team will explain this to you before commencing treatment.
What many folk may not realise, is that similar concerns apply to any medical or other environment where oxygen is used including anesthesia, including dentistry. Fire risk is mitigated in all of these practices.
Knowledge, awareness and action render these environments safe.
© Hayden Dunstan
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