Are school transportation officials taking appropriate precautions when transporting oxygen? The Maryland State Department of Education publishes guidelines for transporting students with this hazardous material on school buses.
A survey taken in the fall of 2000 revealed a common misconception among some school transportation officials in the state of Maryland. These transporters were unaware that students carrying oxygen on school buses in their districts were using liquid oxygen instead of compressed gas oxygen.
At the same time, a report surfaced about a disabled patient suffering severe frostbite on his back from a liquid oxygen spill in an emergency vehicle. This information, combined with a lack of knowledge of liquid oxygen, caused a great deal of concern among transporters.
As a result, the Maryland State Department of Education convened a committee in January 2001 to study the safe use of both gas and liquid oxygen in various school settings, including on the school bus. The committee was made up of transportation, special-education and risk management specialists, health care professionals and attorneys.
The committee produced a comprehensive set of guidelines for managing oxygen in the schools and on school buses. The guidelines represent a major step in establishing best practices for transporting gas or liquid oxygen on school buses.
The decision to transport an oxygen-dependent student on the school bus is the responsibility of the IEP team based on the individual needs of the student. The IEP team and transportation staff should work closely together to determine the best way to manage the physical and medical needs of the student while protecting the safety of others on the bus.
There are questions that need to be addressed before the student begins to ride the bus. Does the student need continuous oxygen or on an as-needed basis? Who should be responsible for adjusting the level of oxygen: the student, the bus assistant or a nurse? What should trigger a 911 call? These are the types of questions that the IEP team should resolve within the context of federal law, individual state laws and school system policies.
Although these are important issues discussed in the Maryland guidelines, they are beyond the scope of this article. The focus of this article is the danger posed by oxygen on the bus and the steps transporters should take to ensure the safety of those traveling with the oxygen.
Characteristics of oxygen
Oxygen makes up 21 percent of the air we breathe. In addition to supporting life, oxygen, along with fuel and heat, is a vital ingredient for ignition and combustion. The oxygen itself doesn’t burn, but it supports and accelerates combustion.
It takes a considerable amount of heat to ignite flammable materials in air. However, it takes much less heat to ignite flammable materials in an oxygen-enriched atmosphere of 23 percent or more. Additionally, some materials that are not flammable in air will burn in an oxygen-enriched atmosphere. The more oxygen present, the less heat it takes to ignite, and the fire will burn more quickly and intensely. In a pure oxygen atmosphere, like that caused by a liquid oxygen spill, even the friction of a shoe hitting the ground has been known to cause ignition.
Pure oxygen gas (GOX) is clear and odorless. It is heavier than air and will settle to collect in low areas. Liquid oxygen (LOX) is light blue and has the consistency of water. It has a boiling point of -297 degrees F and will evaporate to a gas if heated above this temperature. It is extremely cold, or cryogenic. It will instantly freeze tissue, causing acute frostbite. Most materials that come into contact with liquid oxygen immediately become brittle enough to shatter.
Gas vs. liquid delivery systems
Students using oxygen carry an oxygen delivery system containing either compressed GOX or LOX. All delivery systems require a user connection with delivery tubing and a breathing device. The long, clear plastic delivery tubing connects the oxygen supply to the breathing device. The breathing device may be a nasal cannula, face mask or tracheotomy tube.
The compressed gas oxygen is stored in a cylinder under extremely high pressure, about 2,000 pounds per square inch. One inherent danger with compressed GOX is that a valve stem can eject from the cylinder, turning the cylinder into a high velocity missile. Wear, abuse, improper assembly or a forceful impact may cause this type of accident to occur. In one documented case occurring in a hospital, the cylinder shot with such force that it embedded in a concrete wall. Smaller compressed gas units are carried in a shoulder pack, while the larger units are carried in a cart or attached to the patient’s wheelchair or scooter.
LOX is stored in an insulated metal container similar to a thermos. In the portable units, the container and the metal tubing for filling, dispensing and venting are housed in a plastic casing. As the liquid oxygen in the container warms to above -297 degrees, it creates a pocket of evaporated oxygen gas at the top of the container. This evaporated gas is further warmed through a series of coiled tubes and delivered to the breathing device. When this pocket of gas reaches a pressure of about 40 pounds per square inch, the container is designed to vent the excess oxygen through a pressure relief valve. This venting causes a periodic hissing sound that is perfectly normal.
Because portable units are designed to vent pure oxygen gas, they must be stored in well-ventilated areas to prevent an oxygen-enriched atmosphere from building up around the unit. Attached to the top of the insulated container are metal tubes used to fill the container, regulate the flow to the patient and warm the gas. Therefore, the container must be kept in an upright position or dangerously cold liquid oxygen may leak from the unit.
Steps for safe transport
The Maryland guidelines state that oxygen cylinders or containers must be secured in the following manner:
By determining the individual needs of the oxygen-dependent student, establishing common sense procedures for securing the oxygen and thoroughly training drivers and assistants, transporters can reasonably ensure the safety of all students traveling on a bus with oxygen.
Les Douglas is an area transportation supervisor for the Howard County (Md.) Public School System.