Technical Assessment of Dry Ice Limits on Aircraft (2013)

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11 C h a p t e r 3 Carbon Dioxide Exposure Limits The product of sublimation of dry ice is gaseous carbon dioxide. Carbon dioxide is, of course, a natural component of human, animal, and plant metabolism and is a normal con- stituent of the atmosphere, which contains approximately 390 ppm* of carbon dioxide. Exposure to high concentrations of carbon dioxide gas, above 5%, can cause asphyxiation. Since carbon dioxide is much more dense than air, it will settle in low spaces over time, and entry into the area when the carbon dioxide has collected can also result in asphyxiation. However, there are other health considerations as well. The concentration of carbon dioxide gas in the lungs is an important factor in regulating human respiration, and there- fore concentrations lower than those required for asphyxia- tion are harmful. If the concentration of carbon dioxide is 1% (10,000 ppm), a healthy individual will experience tiredness and fatigue. As the concentration builds, the heart rate and breathing rate increase. At 2%, these healthy individuals tend to feel heaviness in the chest and experience deeper respirations. At 3%, the breathing rate and heart rate double, and double again as the concentration reaches 5%. At concentrations above 5%, some individuals can become unconscious and die if not removed from the high carbon dioxide concentration. If a per- son is doing strenuous activities, such as loading or unloading baggage or cargo, the effects will occur at lower carbon dioxide concentrations. General Industrial Exposure Limits The American Council of Governmental Industrial Hygienists (ACGIH) has set workplace exposure limits for carbon dioxide. Their limits are an 8-hour time-weighted average (TWA) of 5,000 ppm, and a 15-min short-term expo- sure limit (STEL) of 30,000 ppm.14 The Occupational Safety and Health Administration (OSHA) personal exposure limit (PEL) is also 5,000 ppm.15 Carbon Dioxide Exposure Limits for Aircraft The carbon dioxide concentration limit for aircraft was established by the FAA, and information on how this limit was determined has been summarized by the U.S. Department of Transportation (DOT) in a published notice entitled “Allow- able Carbon Dioxide Concentration in Transport Category Airplane Cabins, Final Rule.”16 In this document the FAA sets a carbon dioxide exposure limit of 5,000 volume ppm. The FAA document also summarizes the guidelines and limits on carbon dioxide concentrations as set by various other organizations. For convenience, these limits are sum- marized in Table 4. The FAA also provides a definition of the sea-level equivalent measurement conditions associated with the FAA carbon dioxide limit.17 These conditions are 25°C and 760 mm of mercury pressure.* This project uses the carbon dioxide limit already estab- lished by the FAA. It is beyond the scope of this project to provide a critical evaluation of the FAA limit, an analysis of its basis, or a comparative analysis or critique of the FAA carbon dioxide limits with limits set by other organizations. As a side note, in their discussion of indoor air quality, OSHA recommends an indoor carbon dioxide limit and states that “1000 ppm [of carbon dioxide] indicates inadequate ven- tilation; complaints such as headaches, fatigue, and eye and throat irritation will be more widespread; 1,000 ppm should be used as an upper limit for indoor levels.”18 However, this limit is based on the use of elevated levels of carbon dioxide as a surrogate for other air contaminants and as in indicator Review of Guidelines and Regulations for Dry Ice Shipments *This value is for remote areas or high altitudes. The concentration of carbon dioxide in the lower atmosphere shows a spatial variation accord- ing to the proximity to human activity or vegetation; the latter results in diurnal and seasonal variations. *In SI units, 760 mm of mercury pressure equals 101.325 kPa.

12 of a general lack of ventilation of occupied spaces and does not address the health effects of the carbon dioxide itself or the situation where the carbon dioxide in the occupied space results from dry ice sublimation. Dry Ice Packaging Requirements ICAO and IATA Packaging Requirements The International Civil Aviation Organization (ICAO) provides instructions for shipments containing dry ice. The International Air Transport Association (IATA) follows the ICAO instructions. General Requirements Under ICAO instructions, packages containing dry ice are designated as “Class 9 miscellaneous.” The UN packing group is III. This is a low-hazard clas- sification. The maximum net quantity of dry ice per package is 200 kg for both passenger and cargo aircraft. In addition, the packaging must be designed to allow the carbon dioxide generated to vent from the package and thereby not pressur- ize the package. Shipments of Dry Ice in Packages ICAO provides the following special packing instruction (No. 904) for shipments of dry ice in packages:19 Solid carbon dioxide (dry ice) in packages when offered for transport by air must be packed in accordance with the general packing requirements of Part 4, Chapter 1 and be in packaging designed and constructed to permit the release of carbon diox- ide gas to prevent a build-up of pressure that could rupture the packaging. Arrangements between shipper and operator(s) must be made for each shipment, to ensure that ventilation safety procedures are followed. The dangerous goods transport docu- ment requirements of Part 5, Chapter 1 are not applicable pro- vided alternative written documentation is supplied describing the contents. The information required is as follows and should be shown in the following order: UN 1845, (Dry ice or Carbon dioxide, solid), class 9 (the word “class” may be included prior to the number “9”), the number of packages and the net quantity of dry ice in each package. The information must be included with the description of the goods. The net mass of the Carbon dioxide, solid (Dry ice) must be marked on the outside of the package. The general packing requirements of “Part 4, Chapter 1” that are referred to are somewhat lengthy, but generally call for sturdy packaging that can withstand the rigors of shipment. Bulk Shipments and Larger Shipping Containers In the case of bulk shipments, the ICAO instruction No. 904 provides that: Dry ice used as a refrigerant for other than dangerous goods may be shipped in a unit load device or other type of pallet pre- pared by a single shipper provided that the shipper has made prior arrangements with the operator. In such case, the unit load device, or other type of pallet must allow the venting of the car- bon dioxide gas to prevent a dangerous build-up of pressure. The shipper must provide the operator with written documentation stating the total quantity of the dry ice contained in the unit load device or other type of pallet. The ICAO instructions also contain “notified variations from the instructions.” This section contains official noti- fications* of state variations. There is one such variation for Continental Airlines, number CO-9.20 This variation states: The carriage of UN 1845 — Carbon dioxide, solid (dry ice) will be limited to the following established limits: – all narrow-body aircraft (B737, B757, ERJ) – 114 kg per aircraft; – all wide-body aircraft (B767, B777) – 200 kg per aircraft. Organization Limit in Volume, % Limit in Volume, ppm OSHA interim rule 0.5 5,000 OSHA final rule 1.0 10,000 ACGIH short-term exposure limit (15 min) 3.0 30,000 ACGIH 8-hour threshold limit value 0.5 5,000 FAA 0.5 5,000 Table 4. Carbon dioxide exposure limits. *Note that these are notifications only. ICAO is not evaluating or approving the variation.

13 Exception: Due to the limited sublimation rate of dry ice when carried in “refrigerated/insulated” containers, the follow- ing quantities of dry ice may be carried in any containers with the carrier code “PC” or any containers with the prefix code “R”: B777-200 – 1,088 kg B767-400 – 816 kg B767-200 – 635 kg B757-200 – 590 kg B757-300 – 725 kg B737-(all series) – 430 kg The above container limitations are per aircraft. Note: The carrier code “PC” is used for Air Fiji, Ltd. Con- tainers with the prefix code “R” are “Thermal Certified Aircraft Containers” and include the RKN- and RAP-size ULD con- tainers. Our understanding of this exception is that it applies only to ULDs shipped on Continental Airlines/Air Fiji. DOT Regulations for Dry Ice Packaging The Pipeline and Hazardous Materials Safety Administra- tion (PHMSA) places the following requirement on dry ice packaging: 173.217 Carbon dioxide, solid (dry ice). (a) Carbon dioxide, solid (dry ice), when offered for transportation or transported by aircraft or water, must be packed in packagings designed and constructed to permit the release of carbon dioxide gas to pre- vent a buildup of pressure that could rupture the packagings. Packagings must conform to the general packaging requirements of subpart B of this part but need not conform to the require- ments of part 178 of this subchapter. Note that the requirement is on venting and not the con- centration of carbon dioxide in the compartment following the release. Requirement 173.217(b), “Transport by Aircraft,” specifies the requirements that must be met when dry ice is used as a refrigerant in packages offered for shipment on air- craft. The requirements in this section exempt the shipping paper requirements of Part 172 Subpart (c) provided written documentation containing the following information is sup- plied: the proper shipping name of “Dry Ice or Carbon Diox- ide, solid, class 9, UN 1845,” the number of packages and the net quantity of dry ice in each package, and the description of the refrigerated material being shipped. Such packages are also exempt from 49 CFR Part 178, “Specification of Packag- ings.” Provided the requirements in 173.217(a) quoted previ- ously are met, packages containing less than 2.5 kg of dry ice are exempted from all DOT packaging requirements. FAA and NTSB Guidelines An early FAA advisory circular, issued in 1974, discussed the hazard from carbon dioxide from dry ice and presented a method of determining the maximum allowable amount of dry ice. This document recommends using a 5,000-ppm maximum carbon dioxide concentration and a weight-based sublimation rate of 1% per hour.21 Although there have been subsequent notifications and publications, the mass-based sublimation-rate methodology and associated assumptions have not changed. The FAA later issued another advisory circular that echoed the 1974 document.22 This circular was updated in May of 2009 to change the amount of CO2 made by the sublima- tion of 1 pound of dry ice from 8.5 to 8.8 cubic feet.23 Given the other uncertainties in the estimation of carbon dioxide concentrations on aircraft, this difference is not significant.* In 2000 the FAA issued an advisory circular that addressed ventilation requirements for crew and passengers but did not directly discuss the use of dry ice.24 One significant point from this document is that, as part of the discussion of ozone levels, the FAA established an official standard temperature and pres- sure to be used for gas concentration calculations, namely a temperature of 25°C and a pressure of 760 mm of mercury.† In 2001, the National Transportation Safety Board (NTSB) issued a safety recommendation in response to a 1998 inci- dent in Texas.25 In this incident, the crew of a cargo aircraft became short of breath after being exposed to an excessive amount of carbon dioxide from a shipment consisting of 198 packages of frozen shrimp, each containing 2.2 kg of dry ice, for a total of 436 kg of dry ice on the DC-8-51 cargo airplane. The incident occurred after a ground delay without provision for adequate ventilation. More recently, in 2006, the FAA issued a report with data on measured dry ice sublimation rates.26 Although this report will be discussed in more detail later, the document may be summarized by noting that this report retained the original 1974 recommendation to use a mass-based percentage subli- mation rate to determine the amount of dry ice. *This number is discussed in Chapter 9; in particular, see Table 8. †Equivalent to 101.325 kPa.