In addition to worker hazards there is also the potential damage to equipment. This includes contamination of the fuel cells with chips or other foreign objects that may contaminate fuel causing engine failure endangering the crew and passengers during flight.

A fuel cell that has never contained fuel

Even though a dry fuel cell has never contained jet fuel, it still can present a danger to worker safety. If the condition of an open dry fuel cell is questionable, it should always be treated as a wet cell.

Maintenance on aircraft fuel cells consists of inspection, cleaning, sealing, painting and testing operations. When working in fuel cells the development of highly toxic and/or flammable atmospheres as well as oxygen deficient atmosphere is possible particularly in wet fuel cells during topcoating, solvent cleaning and sealing operations. Constant atmospheric monitoring must be provided before and during the duration of entry. Atmospheric conditions inside fuel cells can quickly change as environmental conditions change (such as temperature) and as work is performed.

When testing the atmosphere of a fuel cell, the first test is for presence of oxygen. Fresh air contains

20.9% oxygen with a balance of mostly nitrogen. Fuel cell entry is not permitted if the oxygen level is greater than 23.5% or less than 19.5% by volume, according to OSHA’s standard for confined spaces, Title 29 Code of Federal Regulations (CFR) part 1910.146. Excessive oxygen accelerates combustion and may lead to explosion whereas decreased levels of oxygen can cause unconsciousness and death.

The next test is for explosive atmospheres, generally measured in percent LEL. Levels of flammable vapors greater than 10% LEL are considered not “fire-safe” and no entry is allowed. The final test is to verify presence of toxic vapors. Toxic vapors may consist of solvents used in the cleaning and sealing operations or traces of fuel vapor remaining in the cell. Testing for trace levels of toxic vapors are required to determine if the fuel cell is “health safe.”

Long term exposure to jet fuel vapors has been documented to affect the lungs and nervous system of workers and can cause acute symptoms such as dizziness, headache, nausea, respiratory tract symptoms, palpitations, and chest pressure. When testing aircraft fuel cells for toxic vapor, measurements are generally made in the Parts Per Million (ppm) range. For example, JP-8 Aviation Turbine Fuel consists primarily of Kerosene and a mix of various other hydrocarbons such as n-Octane, n-Nonane, and aromatic hydrocarbons such as Benzene, Toluene, Xylene, and Trimethylbenzene. These components have low threshold limit values (TLV’s) and require monitoring in the ppm range for personal protection.

Selecting the proper monitoring equipment is essential for worker safety. One such instrument designed to meet the demanding needs of aircraft fuel tank entry is the Innova-FV ( Fuel Vapor Monitor). This lightweight portable gas detector is specifically designed to simultaneously monitor for percent oxygen as well as percent LEL or Parts Per Million (ppm) levels of flammable or toxic vapor. This proven technology responds to all flammables that may be present during fuel cell maintenance and is more durable, requires less maintenance, and is not adversely affected by high variations in humidity and temperature as with Photo Ionization Detectors (PID’s).

Calibrated on hexane, which is representative of fuel vapors, the  Innova-FV comes complete with external and internal liquid blocking filters and a 3’ Teflon® lined hose. The monitor uses an extremely stable and quick responding oxygen sensor that is not susceptible to fluctuations in atmospheric pressure, an important feature when using instrumentation inside fuel tanks at a reduced pressure during leak testing operations. In addition, the Innova-FV monitor features a humidity resistant catalytic gas sensor designed to monitor for fuel vapor within the range of 0-100% LEL in 1% LEL increments and 0-1000 ppm in 10 ppm increments. Each Innova-FV monitor also contains internal data logging circuitry for record keeping. The optional data retrieval package allows you to view data on computers using Windows™ 95, 98, or NT operating software.

Although specifically designed for the detection of non-methane hydrocarbons (such as jet fuel or gasoline), the press of a button provides full gas response (including methane) when required. The monitor is now fully functional for use in applications where other combustibles, including methane or natural gas, are present; giving you “full gas” response.