The transport of oxidizers and compressed oxygen within aircraft is heavily regulated, largely as a result of the fatal 1996 ValuJet accident. Past Federal Aviation Administration (FAA) studies have found that released oxidizers can exacerbate burning within a halonsuppressed cargo compartment fire, potentially overwhelming the fire suppression system within an aircraft.

Recently, a request was submitted to ship medical devices containing small quantities of gaseous nitrous oxide (N2O). As part of the certification process, the manufacturer of this device completed the PHMSA-required thermal resistance and flame penetration tests; however, the packaging was unable to pass the thermal resistance portion of the required tests and small quantities of N2O were able to escape. As a result of these initial tests, the manufacturer requested an exemption from this requirement.

PHMSA requested assistance from the FAA Fire Safety Branch to determine if quantities of released N2O would significantly impact a cargo compartment fire. Although N2O is not flammable, it is an oxidizing agent that could exacerbate an otherwise controlled cargo compartment fire, and ultimately overwhelm the integrity of the suppression and containment capabilities of the system. Tests were conducted within an aircraft lower deck (LD-3) sized steel test chamber using a fire load of eighteen cardboard boxes filled with shredded paper. During each test, the shredded paper was ignited and the ensuing fire was allowed to develop. Two baseline tests were first conducted, in which the fire within the test chamber was allowed to burn unabated, without introducing N2O. Three subsequent tests were conducted in which various quantities of N2O gas (5.8 oz, 11.6 oz, and 17.4 oz) were released into the testchamber once the fire was fully developed.

Results indicated that released quantities of N2O less than or equal to 11.6 oz did not produce a significant reaction within the fire in the test chamber. However, it was observed that as the quantity of released N2O increased, more significant combustion reactions occurred. Therefore, until further data is acquired, it is recommended that the amount of N2O be limited to no more than 11.6 oz per Unit Load Device (ULD) for air transport.

A thermal event involving a package containing lithium-ion pouch cells occurred within a sorting facility of an all-cargo airline in December 2022. This package had been previously shipped via air and was being handled for delivery to its next destination. Following the incident, the package was sent to the William J. Hughes Technical Center for further evaluation using battery analysis equipment to determine the as-delivered state of charge (SOC) of the cells.

Lithium-ion cells not packed with or contained in equipment (Lithium ion batteries, UN3480) that are transported via aircraft are mandated by Federal regulations to be at a SOC no greater than 30%. Previous FAA studies have determined that lithium-ion cells exceeding this level are a serious hazard due to risk of thermal runaway and can lead to an unsafe condition on an aircraft.

Upon inspection, many of the cells in the package were observed to have significant signs of damage, including swelling and corrosion. However, it could not be determined if this damage occurred prior to or after the incident. SOC testing was performed on cells that did not show significant signs of damage. Testing determined that 14 of the 25 tested cells exceeded the maximum 30% SOC requirement. Of these 14 cells, 7 exceeded 70% SOC, with the highest evaluated cell recording a SOC of over 90%.

This report documents proven methods of collection and analysis for acid gases in fire tests conducted at the FAA Technical Center. It focuses on methods of collection and analysis requiring trapping hot acid gases at the sampling point and avoiding errors due to sample line losses. The sampling system, collection tubes and procedures are described in this report. Various ion chromatography methods are described which separate and quantify the solution concentration of the anions corresponding to the gases HF, HCl, HBr, HI, HCN, H2S, HIO3, H3PO4, NOx and SOx in complex combustion gas matrices. The ion chromatography methods include the separator columns, suppressor columns, eluents, detectors and autosamplers. The fluoride ion selective electrode method is also evaluated

Suitable alternatives to Halon 1301 are being sought throughout the aviation industry as a result of a worldwide agreement to ban the production and use of Halon 1301 due to the detrimental effects to the atmosphere. Fire extinguishing agents proposed for usein transport category airplane cargo compartments must demonstrate effective firefighting performance against the types of fires likely to occur in airplane cargo compartments. The Federal Aviation Administration (FAA) developed a minimum performance standard (MPS) evaluation method to compare the efficacy of any proposed agent against the known performance of Halon 1301. In this study the FAA Technical Center (FAATC) Fire Safety Branch evaluated VERDAGENT®, a potential fire suppression agent, in the FAATC Full Scale Fire Test Facility. Tests were performed according to procedures outlined in the MPS. VERDAGENT® is a blend of two components – carbon dioxide and 2-bromo-3,3,3-trifluoroprop-1-ene (i.e., 2-BTP, commonly called Halotron BrX). The MPS was originally designed considering single component agents similar to Halon 1301. Evaluation of a multicomponent agent required supplementary tests to investigate component separation and uniformity of dispersion throughout the cargo compartment. An additional challenge fire test, not within the scope of the MPS, was also performed. This fire load consisted of lithium-ion batteries and a combination of ordinary combustible materials and flammable liquids. VERDAGENT® demonstrated successful performance in the MPS. Component separation was not observed, and the agent was found to disperse uniformly in the cargo compartment. The agent also performed effectively against the additional challenge fire test. The results summarize that VERDAGENT® met the requirements of the MPS for aircraft cargo compartment Halon replacement fire suppression systems.

A simulated model of a full-sized aircraft cargo compartment was used to determine the effect of active cargo containers. Physical testing in conjunction with the simulated cargo compartment was used to validate the accuracy of the Fire Dynamics Simulator model which included an artificial smoke generator. The artificial smoke generator is currently used in certification of smoke detectors in aircraft cargo compartments. It consisted of heaters that vaporize oil to create smoke.

Arranging cargo containers with the smoke generator gives a baseline for smoke movement in the compartment. The smoke was measured using lasers and light meters which were partially obscured by the moving smoke. Fans were added to the containers as a stand-in for temperature-controlled cargo containers (TCC), also called “active” cargo containers, that had condenser cooling fans

Comparing the experimental test data to the simulated test data showed that the simulation is a good fit. The smoke trends between the tests are very similar and there was a difference in detection time typically less than 10 seconds over the entirety of the tests.

Using the Envirotainer RKN e1 as a typical TCC, an airflow of 35 CFM was used for the experimental testing. According to the testing and simulations, using TCCs with airflows of 17.5 or 35 CFM has an inconsistent effect on the smoke detection time, at the extremes, ±20 seconds, ±30% of detection time. At elevated airflow of 70 and 140 CFM, the time to smoke detection was almost always delayed, an average of 30 seconds (+50%) and at most up to 70 seconds (+110%). Delay of smoke detection could cause potentially dangerous conditions in the aircraft. Because of the delay, it is recommended to keep airflow of TCCs to below 70 CFM.