1998 q4h-azards of airplane fuel-tank entry

8/13/2019 1998 Q4H-Azards of Airplane Fuel-Tank Entry

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Hazards of Airplane Fuel-Tank Entry

A large percentage of the work involved in properly inspecting andmodifying airplane fuel tanks and their associated systems must be

done in the interior of the tanks. Performing the necessary tasksrequires inspection and maintenance personnel to physically enter thetank, where many environmental hazards exist. These potential hazardsinclude fire and explosion, toxic and irritating chemicals, oxygendeficiency, and the confined nature of the fuel tank itself. n order toprevent related in!uries, operator and repair station maintenanceorganizations must develop specific procedures for identifying,controlling, or eliminating the hazards associated with fuel"tank entry.#aintenance personnel who enter airplane fuel tanks to inspect or modify them

face several potential hazards. These include exposure to flammable and toxicchemicals, potentially harmful atmospheric conditions, and the confined interiorstructure of the tank. $perators and repair stations can protect maintenancepersonnel from these hazards by developing safety procedures for fuel"tank entrypersonnel. To successfully prevent related in!uries, both operators andmaintenance personnel must understand the following%

&. 'uel"tank hazards.(. Preparation for entry.). *onditions required for entry.+. mergency response plan.

-.

Fuel-Tank HazardsThe potential dangers that fuel"tank personnel may experience presentthemselves in one of two forms%

*hemical.

Physical.


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The most commonly recognized hazard of fuel"tank work is the !et fuel itself. 0etfuel is a flammable liquid and can be ignited given certain ambient conditions,primarily temperature and vapor concentration. The temperature at which thevapors of a flammable liquid can ignite is known as the 1flash point.1 A hazardous

vapor concentration is present when a fuel vapor reaches a level known as thelower flammability limit 2/'/3 or lower explosive limit 2//3. These limits areusually expressed as a percentage by volume. 'uels below the /'/4// areconsidered too lean to burn. f the fuel vapor concentration exceeds the upperflammability limit or upper explosive limit, the fuel is considered too rich to burn.

A fuel vapor concentration between these two limits is considered to be in itsflammable range and will ignite and burn if exposed to an ignition source. $ne ofthe best ways to control unwanted fires and explosions is to keep the fuel vaporconcentration below the /'/4//, preventing it from reaching its flammablerange 2figure &3.$ther flammable chemicals may also be present during fuel"tankwork. *hemicals with a low flash point 2less than 567' 2(&7*33, such as methyl

ethyl ketone 2#83, are even more hazardous than !et fuel, and their use mustbe strictly controlled.

*hemicals, including !et fuel, may also present toxic or irritant hazards. At highconcentrations, !et fuel and other hydrocarbons can affect the nervous system,causing headache, dizziness, and lack of coordination. *hemicals may alsocause chronic health problems, such as liver and kidney damage. *leaningsolvents, sealants, lubricants, and other chemicals used in fuel"tank work canalso cause irritating effects to the skin if not controlled.P9:*A/

The physical characteristics of the tank itself can create hazards and can alsoexacerbate fire, explosion, and toxicity hazards. ntry into most airplane fueltanks is through an oblong hole less than two ft 26.; m3 long and one ft 26.) m3wide. Though the interior dimensions of fuel tanks vary considerably, with thewing center tanks in widebody !ets the largest, all fuel tanks have a limitedvolume. A relatively small amount of a chemical inside one of these enclosedspaces can create significant levels of flammable or toxic vapor.
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The single most important method of controlling the fire, explosion, and toxichazards associated with working in an open fuel tank is ventilation. The morefresh air that is present in the fuel tank, the safer the environment will be formaintenance personnel. *ontinuously pushing fresh air into a fuel tank helps to

prevent a fuel vapor concentration from reaching its /'/, thus preventing firesand explosions. 'resh air also dilutes the vapor concentration of toxic chemicals,reducing the risk of hazardous exposures. igh volumes of fresh air will alsoprevent a condition known as oxygen deficiency. >ormal concentration ofatmospheric oxygen in air is about (& percent. At oxygen"deficient levels 2&D.-percent and below3 a person will begin to exhibit signs of oxygen starvation,including headache, nausea, drowsiness, and slurred speech. At increasinglylower oxygen concentrations, more severe reactions occur. ?ltimately, death byasphyxiation is possible.

$xygen deficiency is often caused by physically displacing the oxygen in a

space. 'or example, pumping nitrogen into a fuel tank to prevent fire ignition willcause the oxygen concentration to decrease. $xygen deficiency can also becaused by the oxidation of some material, which can use up the available oxygenwithin a space. $xidation is a chemical reaction that combines atmosphericoxygen with some other material to form an oxide. ron oxide, commonly knownas rust, is an example.'$//$< @*$##> C>T/AT$> T*>B?:

The physical structure of airplane fuel tanks presents some unavoidablechallenges in ensuring adequate ventilation. :ome of the challenges includedead air spaces and small openings between tank sections that inhibit air flow,

ventilation equipment that may not be selected or set up properly, or suspensionof ventilation before the entry work is completed. Planning and execution arecritical to providing adequate ventilation.

The recommended practice for conducting tank ventilation is the push"pulltechnique. 'irst, an upstream 1push1 access hole should be opened. >ext, adownstream 1pull1 hole should be opened. 'inally, a blower should be located at


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the push hole, forcing fresh air into the tank. xhaust equipment can be locatedat the pull hole to supplement the airflow through the tank. P@$P@/9 #$>T$@ A@ > '?/ TA>8:

>o maintenance personnel should enter a fuel tank until it has been adequatelyventilated. To determine if the atmosphere in the tank is suitable for entry, theatmospheric conditions should be checked and continuously monitored foroxygen concentration, flammable vapor concentration, and toxic vaporconcentration.

ntry should not be permitted unless the oxygen concentration is between &D.-and ().- percent. *oncentrations below &D.- percent are considered oxygen"deficient. *oncentrations above ().- percent are considered oxygen"enrichedand significantly increase the risk of fire and explosion. #aintenance personnelshould not be permitted to enter the tank if either of these conditions exists.

nstruments are available that can simultaneously monitor the oxygenconcentration and flammable vapor concentration, but the measurement ofoxygen concentration is the most critical. Any measurements outside of thepermitted range can significantly threaten the safety of entry personnel and cancause faulty readings of other monitoring devices, especially those used to detectflammable vapors.

nstruments used to monitor flammability must be calibrated for the type offlammable vapor determined to be present. 'or 0et"A"type !et fuels, a flammablegas monitor calibrated with hexane will be reasonably accurate. f other types of

!et fuels are present, the monitor must be calibrated according to thecharacteristics of the fuel. n many cases, the specific characteristics of the fuelmay be unknown, so allowances in instrument accuracy should be considered. fother flammable chemicals are present, such as #8, specifically calibrateddevices will be needed to monitor for the presence of these vapors.

nstruments are also available for monitoring potentially toxic atmospheres.Again, specific instruments and monitoring techniques must be selected basedon the type of chemical present. $perators and repair stations should consultsafety and industrial"hygiene professionals for recommendations on dealing withtoxic chemicals.

Conditions Required For EntryThe most important factor in preventing in!ury during fuel"tank work is a properlytrained and equipped entry crew. The entry crew is composed of the entrysupervisor, the standby attendant, and the entry personnel. The entry supervisorauthorizes the work and ensures that it is conducted according to procedure. Thestandby attendant stays outside of the fuel tank to monitor conditions in andaround the work area. The standby attendant is authorized to order evacuation ofthe fuel tank if conditions change and put the entry personnel at risk. ntrypersonnel enter the fuel tank and perform the work. They must be able to


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recognize potential hazards and evacuate the tank if working conditionsdeteriorate.ndividually and together, the members of the fuel"tank entry crewmust be aware of the following requirements for safe working conditions%

*ommunication.

@espiratory protection. Centilation and air monitoring.

lectrically powered equipment.

Airplane damage considerations.

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*ontinuous voice communication should be maintained between entry personneland the standby attendant throughout the entry process. Coice communicationcan be assisted by radio or electronic equipment, but these devices must berated for use in potentially flammable 2classified3 atmospheres.@:P@AT$@9 P@$T*T$>epending on the atmospheric hazards present, entry personnel may berequired to wear respiratory protection. Air"purifying respirators can be used if theoxygen concentration is at least &D.- percent. f the potential exists for oxygendepletion, or if chemical exposure levels are above the permissible exposurelevel 2P/3, supplied"air respiratory protection may be required. n any situation,safety or industrial hygiene professionals should be consulted for specificrecommendations.C>T/AT$> A> A@ #$>T$@>E

'resh air should be supplied to the fuel tank throughout tank entry. f ventilationis suspended, tank entrants should evacuate the tank until the ventilation can be

re"established. The atmospheric conditions of the tank should also be monitoredthroughout tank entry. f the oxygen concentration levels drop below &D.- percentor rise above ().- percent, tank entrants should immediately evacuate the tank.f flammable vapor levels exceed &6 percent of the /'/ or if toxic vaporconcentrations exceed the P/, tank entrants should evacuate the tank./*T@*A//9 P$T#aintenance technicians may need to use a variety of energized equipment,including lighting, testing equipment, and powered tools. All electrically poweredequipment must be intrinsically safe or rated for use in a potentially flammableatmosphere. Pneumatic tools should be powered only by compressed air, not by

nitrogen or other inert gas that could displace the oxygen inside the tank. A@P/A> A#AE *$>:@AT$>:

Personnel performing fuel"tank entry work may damage the airplane if they arenot properly trained to avoid such damage. The mating surfaces of the accesshole and covers should be protected during entry so that the surfaces are notscratched or otherwise damaged. The components inside fuel tanks, such as fuelpumps, fuel"quantity systems, and associated wiring and conduits, are also


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vulnerable to damage if they are struck or dislodged. 'inally, the containmentproperties of the fuel tank can be compromised if the sealant is damaged ordislodged or if fuel"tank bladders are penetrated.

Emergency Response Plans

'uel"tank work procedures must also address the potential for emergencysituations. f specific response procedures are not developed, an emergencysituation may result in severe in!ury or death to maintenance personnel.$perators and repair stations should prepare procedures for maintenancepersonnel to follow in the following four situations%

ntrant self"evacuation. Attendant"ordered evacuation.

Air monitor alarms.

?nresponsive tank"entrant rescue.

>T@A>T :/'"CA*?AT$>The tank entrant must be able to recognize the hazards of working in an airplanefuel tank and should be ready to evacuate if conditions change, including theentrant=s own psychological state. ntry into enclosed spaces can induceuncontrollable claustrophobia, resulting in panic and an inability to functionnormally. Tank entrants should be trained to recognize the beginning stages ofclaustrophobia and what to do when this occurs.

ATT>A>T"$@@ CA*?AT$>

The standby attendant must continually monitor conditions in and around thework area. f conditions change and potentially put the tank entrant at risk, theattendant should order the entrant to evacuate the fuel tank. The attendantshould be trained to recognize symptoms of oxygen deficiency and overexposureto toxic chemicals and should closely monitor the physical state of the tankentrant. f the tank entrant exhibits adverse symptoms, the attendant shouldorder the tank entrant to evacuate the tank.

A@ #$>T$@ A/A@#:

f the instruments used to monitor atmospheric conditions in the tank go into analarm mode, the tank entrant should immediately evacuate the tank. The specificcondition causing the alarm should be identified and corrected before work insideof the tank can continue.

?>@:P$>:C TA>8">T@A>T @:*?f for any reason the tank entrant becomes unresponsive, the standby attendantshould immediately initiate rescue procedures, including immediate notification ofemergency response assistance. The standby attendant should then ensure thatfresh air is being supplied to the tank entrant. All ventilation equipment should bechecked, and more ventilation should be supplied if available. Additional accessholes should be opened if possible.


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Personnel entering a fuel tank for rescue purposes must be specially trained inrescue techniques and should be provided with appropriate rescue equipment,including supplied air and self"contained breathing apparatus.

Summary

Airplane fuel"tank entry is necessary for inspection and modification but can posehazards to maintenance personnel performing the work. 'uel"tank work can beaccomplished as required without placing personnel at risk through effectivepreparation and training. $perator and repair station airplane maintenanceorganizations can provide a safe, healthy work environment for fuel"tankpersonnel by identifying potential hazards, developing control measures, andinstructing personnel in the specific procedures to be followed during fuel"tankwork.""""""""""""""""""""""""""""""""""""""

lossary of Terms

'/A##AF/ @A>E

The fuel vapor4air concentrations between the lower and upper flammability limit.A fuel"vapor concentration in the flammable range will support combustion.

'/A: P$>T

The minimum temperature at which the vapors of a flammable liquid will ignite.

>T@>:*A//9 :A'

lectrically powered equipment that has been designed and built to eliminateand4or contain potential ignition sources due to the electricity in the device. Alsoknown as 1explosion proof.1

/$


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1998 q4h-azards of airplane fuel-tank entry

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