(1) New agents introduced after the effective date of this AC should comply with the provisions of paragraph 2a through 2e above.
(2) If the documentation needed in paragraph 2f(1) is not yet officially published for a particular halocarbon agent, use the NOAEL values approved under the SNAP program mentioned in paragraph 2a(1) above. They can be obtained from the SNAP Program Coordinator at the EPA Office of Air and Radiation or on the public docket for that office and used to determine safe-use W/Vs in the absence of published FAA safe-use guidance. Safe-use W/Vs may be calculated using EPA's NOAEL values following the methodology outlined in appendix 3 reference paragraph 7m of this AC.
(3) The FAA Technical Center (FAATC) intends to publish future guidance on handheld extinguishers. This guidance will include safe-use W/V for ventilated compartments using FAA approved fire extinguishers containing halon replacement agents introduced after the issuance of this AC.
3_ How are Halon Extinguishers Approved?
a. National Certification. Required halon hand-held fire extinguishers approved for use on aircraft should have a minimum rating of UL 5B:C. Halon 1301 and Halon 1211/1301 blends are also used. Halogenated fire extinguishers must comply with U.S. - UL 1093, Halogenated Agent Fire Extinguishers, or equivalent, for Halon 1211, Halon 1301 and Halon 1211/1301 blends per U.S. - UL 711 or equivalent (see paragraph 1b above). It should be noted that on March 12, 2009, UL announced the withdrawal of US - UL 1093 and the continuance of existing certifications to the withdrawn US - UL 1093. UL will no longer accept the submittal of new or revised products, but all current compliant products covered under US - UL 1093 will continue to be authorized to bear the classification mark of Underwriters Laboratories Inc. until October 1, 2014.
b. Specifications for Approved Halon Agents. For hand fire extinguishers that still employ halogenated agents, only Halon 1211, Halon 1301, or blends of the two have been previously approved and used aboard aircraft. The following specifications cover the requirements for halogenated agents:
(1) Halon 1211 should meet the requirements of ASTM D7673-10, Standard Specification for Halon 1211-Bromochlorodifluoromethane (CF¿CIBr)), or ISO 7201-1:1989, Fire protection -- Fire extinguishing media - Halogenated Hydrocarbons - Part 1:
Specifications for Halon 1211 and Halon 1301.
(2) Halon 1301 should meet the requirements of ASTM D5632-08, Standard Specification for Halon 1301-Bromotrifluoromethane (CF Br)), or ISO 7201-1:1989.
(3) Hand fire extinguishers with halon agents may continue to be used on aircraft as long as recycled halon of proven acceptable quality is available. Recycled agents are still available for purchase, but the duration of their availability is unknown. Therefore, we encourage operators to consider replacing halon extinguishers after discharge with approved halon replacement extinguishers.
(4) An EPA exemption allows the production of halon blends from recycled halon for aircraft use. There are strict conditions to this exemption.
(5) Fire extinguisher manufacturers are responsible for the validation of agent purity whether using new or recycled agent.
Marking. If you are a manufacturer, mark your halon extinguishers permanently and legibly with the name of the listing agency and rating according to U.S. - UL 711 or equivalent.
U.S. - UL extinguishers must have the UL listing mark (include UL copyright logo) with the four required elements: UL in circle mark; word "listed;" product or company name; and issue/serial number or control number. FM extinguishers must have the FM listing mark. And, USCG extinguishers must have the "USCG approval 162.028/XX" marking.
Chapter 3. Selecting the Correct Hand Fire Extinguisher
1. What are the Different Types of Fires?
Classes of Fires. To properly select an appropriate hand fire extinguisher for use in an aircraft, you should consider the following classes of fires that are likely to occur onboard your aircraft, as defined in the appendix 3, paragraph 1 la of this AC.
(1) Class A. Fires involving ordinary combustible materials, such as wood, cloth, paper, rubber, and plastics.
(2) Class B. Fires involving flammable liquids, petroleum oils, greases, tars, oil base paints, lacquers, solvents, alcohols, and flammable gases.
(3) Class C. Fires involving energized electrical equipment where the use of an extinguishing media that is electrically nonconductive is important.
(4) Class D. Fires involving combustible metals, such as magnesium, titanium, zirconium, sodium, lithium, and potassium.
Lithium Battery Fires. Do not treat a fire involving a small number of lithium batteries as a Class D fire. We consider a small number of rechargeable lithium batteries as what would be found in portable electronic devices (PED) e.g. laptop computers, cell phones, pagers, audio/video/data recording or playback devices, messaging devices, personal digital assistants (PDAs), and two-way radios. See chapter 4 paragraph 1f of this AC on fire fighting training for further information.
2. What do the Numeral Ratings Mean? The labeling on fire extinguishers consists of numerals and letters used in combination to describe the extinguishers relative effectiveness on a specified Class/type(s) of fire(s).
Numerals are used with identifying letters for extinguishers labeled for Class A and Class B fires. The "numeral," which precedes the letter, indicates the relative extinguishing effectiveness of the device on a given size fire. This is dependent on the agent, the capacity of the device, discharge times, and design features. For example, an extinguisher rated as U.S. - UL 4A should extinguish about twice as much Class A fire as a U.S. - UL 2A rated extinguisher.
Numeral ratings are not used for extinguishers labeled for Class CorD fires. Extinguishers that are effective on more than one class of fires have multiple "numeral-letter" and "letter" classifications and ratings; for example, U.S. - UL 5B:C.
b. Additional Rating Guidelines for Halocarbon Extinguishers. For occupied spaces on transport category aircraft, extinguishers employing halocarbon clean agents, replacing required Halon 1211 extinguishers, should have a minimum U.S. - UL 5B:C or an equivalent rating. Halocarbon extinguishers are most effective on Class B and C fires. Extinguishers with greater capacity are also rated for Class A fires. Extinguishers with a 2B:C or 5B:C U.S. - UL rating, although not rated for use on Class A fires, have been shown to be effective in extinguishing surface Class A fires.
3. What Extinguishing Agents are Appropriate for the Different Types of Fires? The following extinguishing agents are appropriate for use on the types of fires specified in paragraph la above:
a. Water. Class A type fires are best controlled with water by cooling the material below its ignition temperature and soaking the material to prevent re-ignition.
b. Carbon Dioxide. Class B or C fires are effectively controlled by carbon dioxide as a blanketing agent.
Note: Carbon dioxide is not recommended for hand-held extinguishers for internal aircraft use.
Dry Chemicals. Class A, B, or C fires are best controlled by dry chemicals. The only "all purpose" (Class A, B, C rating) dry chemical powder extinguishers contain monoammonium phosphate. All other dry chemical powders have a Class B, C U.S - UL fire rating only.
Note 1: In general, dry chemicals are not recommended for hand extinguishers for internal aircraft use, due to the potential for corrosion damage to electronic equipment, the possibility of visual obscuration if the agent were discharged into the flight deck area, and the cleanup problems from their use.
Note 2: When approving a non-gaseous agent for installation on aircraft, evaluate the contamination impact to the structure, wiring and surrounding systems, and consider potential mixing of the agent residue with water. Using such extinguishers may require specific maintenance procedures addressing cleanup.
d. Halons. Class A, B, or C fires are appropriately controlled with halons. However, do not use halons on a class D fire. Halon agents may react vigorously with the burning metal.
Note: While halons are still in service and are appropriate agents for these classes of fires, the production of these ozone depleting agents has been restricted. Although not required, consider replacing halon extinguishers with halon replacement extinguishers when discharged.
Halocarbon Clean Agents. (Halons are a subcategory of halocarbons.) Class A, B, or C fires are appropriately controlled with the use of halocarbon clean agents. Never discharge halocarbon clean agents or water on a Class D (burning metal) fire. Halocarbon agents may react vigorously with the burning metal.
f. Specialized Dry Powder. Class D fires are best controlled by dry powder. Follow the recommendations of the extinguisher manufacturer because of the possible chemical reaction between the burning metal and the extinguishing agent.
Note 1: Specialized dry powder is not recommended for hand extinguishers for internal aircraft use.
Note 2: Fires involving a small number of Lithium primary batteries (containing molten Lithium) should not be treated as class D fires and specialized dry powder should not be used. See chapter 4, paragraph 1f of this AC for a discussion of appropriate extinguishing agents for Lithium battery fires.
4. What Extinguishing Agents are Compatible with Aircraft Materials?
Corrosion by Extinguishing Agents. Halocarbon clean agents are not corrosive, but review the material compatibility properties for acceptability to aircraft materials. Water itself is not corrosive, but may be rendered corrosive by the addition of antifreeze solutions. Specialized dry powder and monammonium phosphate dry chemical are corrosive to most sensitive electronic components and instruments.
b. Material Compatibility. Halocarbon clean agents can be used in numerous aircraft applications and it is important to review the materials of construction for compatibility when designing new equipment, retrofitting existing equipment, or preparing storage and handling equipment to incorporate halocarbon clean agents. Materials that should be considered include metals, elastomers, and plastics. Halocarbon clean agents or water should never be discharged on Class D (burning metal) fires. These agents may react vigorously with the burning metal.
See paragraph Ib above for the exception: Lithium battery fires involving carry-on appliances.
c. Corrosivity of Decomposition Products. The thermal decomposition products of halocarbon extinguishing agents are corrosive, particularly the acid halides: HF, HCI and HBr.
The decomposition products of burning aircraft materials are also corrosive. Yet decomposition products are minimized by quickly extinguishing the fire. Acid halide production is also based on the agent used and the size of the fire.
What are the Operating Temperature Tolerances?
Halocarbon clean agent extinguishers should operate properly after being conditioned at -40°F (-40°C) or -65°F (-54°C) as applicable and 120°F (49°C) for 16 hours as specified in U.S. - UL 2129 or U.S. - UL 1093, as applicable. Water extinguishers should be protected to -40°F (-40°C) by adding antifreeze and stipulated on the extinguisher nameplate.
Cold operation may require additional consideration in the selection of an extinguisher. This is particularly true for general aviation aircraft in extremely cold climates.
The hidden fire extinguishment tests in the MPS were conducted on halocarbon extinguishers equilibrated to 70°F. More agent, a lower boiling point agent, or an extinguisher design change, may be needed to extinguish hidden fires. Testing may be needed to select an appropriate extinguisher. The boiling points of the halocarbons (at 1 atmosphere) listed in this AC are:
(1) HCFC Blend B = 80.6°F (27.0°C),
(2) HFC-227ea 1.9°F (-16.4°C),
(3) HFC-236fa = 29.5°F (-1.4°C),
(4) Halon 1211 = 26.0°F (-3.4°C), and
(5) Halon 1301 = -72.0°F (-57.8°C).
6. General Guidelines for Hand Fire Extinguishers.
a. Consider the effects of agent toxicity, aircraft ventilation, agent stratification and hypoxia when selecting and sizing the necessary fire extinguisher for your specific application.
Chapter 4 of this AC provides more details.
Provide the required minimum number of hand held extinguishers. See chapter 5, paragraph 4 of this AC. All extinguishers must have the proper U.S. - UL rating, even in spaces where the safe use guidelines, as outlined in chapter 4 paragraphs 2, 4, 5, and 6 of this AC, are exceeded. The failure to extinguish a fire has catastrophic consequences for all aircraft occupants. Agent toxicity should be considered secondary to the immediate need to extinguish the fire.
Follow the safe-use guidance recommendations in chapter 4 of this AC for selecting extinguishers for your aircraft compartments to, "...minimize the hazard of toxic gas concentration...", mentioned in 14 CFR §§ 23.851(c)(2), 25.851(a)(8), and 29.851(a)(3).
d. Do not substitute two smaller extinguishers for one extinguisher of the proper UL rating, except as provided for accessible cargo compartments, as noted in chapter 4, paragraph 5c of this AC. The fire can grow quickly prior to the discharge of the second extinguisher.
e. Due to the relatively short discharge time of hand fire extinguishers: a U.S. - UL 5B and a U.S. - UL 1A: 10B:C rated extinguisher at approximately 8 seconds; and 13 seconds for a U.S. - UL 2A:10B:C extinguisher; training on the proper use of the fire extinguishers is very important.
f. For access to under seat, overhead, and other difficult to reach locations, hand extinguishers equipped with a discharge hose or adjustable wand mounted directly to the extinguisher are highly recommended. A discharge hose or adjustable wand is preferred because it is likely to result in the extinguisher being properly held in an upright position during use and provides a means of directing a stream of agent to more inaccessible areas. Adjustable wand or fixed nozzle extinguishers allow for one-handed use. See AC 120-80 for more details and guidance on in-flight fire fighting. A video for flight crew training is available from the FAA.
The title of the video is "Aircraft In-flight Fire Fighting." The tape version of the video is referenced as "MST 730" and the DVD version is referenced as "MST 730.01." It can be obtained from Dale Dingler, FAA William J. Hughes Technical Center, Advanced Imaging Division, AJP-7960, Atlantic City International Airport, NJ 08405, phone: (609) 485-6646, email:dale.dingler@faa.gov. The in-flight training video is also available at the following public website: http://www.fire.tc.faa.gov/2007Conference/session_details.asp?sessionID=26.
g. U.S. - UL 5B:C extinguishers should have no less than an & foot (3 m) throw range (passing the MPS seat tests assures a 8 foot throw range). Longer throw ranges of 10 feet and greater provide a significant advantage in fighting fires in large transport category aircraft. See appendix 4, paragraph 1 of this AC for more information on replacement agent throw ranges.
h. Halocarbons that are gaseous upon discharge have a more limited throw range.
Halocarbons have discharge characteristics dependent on the halocarbon, nozzle design, extinguisher super pressurization, cold soak times, and operational temperatures.
7. Replacement of TSO Water Extinguishers:
a. Halon replacement extinguishers with a minimum rating of 5B:C can be used in place of required technical standard order (TSO) C19 water extinguishers, if you can show that the replacement extinguisher has comparable or better Class A extinguishing performance than the TSO'd water extinguisher. A TSO C19 water extinguisher can fight small Class A fires but are not large enough to have a 1A rating. The halon replacement extinguisher must have a sufficient throw range to extinguish fires likely to occur.
b. For aircraft that are required to carry two or more extinguishers and two water extinguishers are in close proximity, the two water extinguishers may be replaced by one halon replacement extinguisher. This is allowed only if the extinguisher has been shown to have comparable or better Class A fire extinguishing capability as both water extinguishers and a sufficient throw range to extinguish fires likely to occur.
Chapter 4. Safe Use of Hand Fire Extinguisher
1. What Basic Fire Fighting Training Should be Provided?
a. Flight crewmembers should be trained on the urgency of immediate and aggressive extinguishment of an onboard fire. As fires can grow exponentially with time, the risks of exceeding the hazardous concentration levels of extinguishant are considered minimal compared to the risks of an in-flight fire.
(1) Quickly extinguish the fire.
(2) Immediately turn off all air recirculation systems, as permitted by your flight manual.
b. Train flight crewmembers on the proper use of hand extinguishers. See AC120-80, In-Flight Fires, for additional guidance. A training video on the use of hand extinguishers to fight on-board fires is available at the following website:
http://www.fire.tc.faa.gov/2007Conference/session_details.asp?sessionID=26.
c. Operators should ensure that all crew members receive proper training in the appropriate use of hand fire extinguishers onboard their aircraft
d. Attack the base of the fire at the near edge of the fire and then move the fire extinguisher nozzle with a side-to-side sweeping motion, progressing toward the back of the fire.
The optimum firefighting technique differs for each approved extinguisher.
e. Do not direct the initial discharge at the burning surface at close range, if the burning material might splash and/or splatter.
Lithium Battery Fires. Crew members should be trained not to treat a small number of lithium batteries as a Class D fire. Halon, Halon replacement, or water extinguishers can be used to control fires involving a small number of rechargeable lithium batteries as found in PED e.g. laptop computers, cell phones, pagers, audio/video/data recording or playback devices, messaging devices, PDAs, and two-way radios. Water or other water based liquid from any available source should be poured over the cells immediately after fire knockdown or extinguishment, since only water or water based liquids can provide sufficient cooling to prevent re-ignition and/or propagation of the fire to adjacent cells of the battery pack. A water extinguisher, by itself, can be used safely (from a distance) to extinguish a lithium battery fire and will usually cool it sufficiently to end the event. If needed, it can be followed up by water from any available source.
(1) Crew members should be trained not to use fire resistant burn bags to isolate burning Lithium batteries. Transferring a burning appliance into a bur bag may be extremely hazardous.
(2) See SAFO 09013 and the training video referred to in paragraph 1b above for further guidance on how to fight Lithium battery fires.
2. What are Some General Guidelines for the Safe-Use of Halocarbon Extinguishers?
a. Quickly Extinguish the Fire. Although exposure to halocarbon agents and their decomposition products are a concern, it is far less of a concern than the consequences of an unextinguished in-flight fire. It is critically important to quickly extinguish an in-flight fire. The consequences of an unextinguished in-flight fire include the loss of the aircraft and its occupants and immediate toxic hazards from exposure to thermal decomposition products of the burning materials, including carbon monoxide, hydrogen cyanide, smoke, heat, and subsequent oxygen depletion.
b. Control Exposure to Combustion Gases and Halocarbon Vapors. The following guidance is affected by and may be adjusted for agent stratification and localization, as discussed in chapter 4, paragraph 4b(4).
(1) Turn off all air recirculation systems immediately, if allowed by your aircraft flight manual (AFM) or flight crew operations manual (FCOM). Halocarbon agents are much heavier than air and under most conditions they stratify with time at lower levels. Turning off the recirculation allows the agent entering the low level air returns to be directed to the air outflow valves and out of the aircraft. This increases the rate of agent removal from the aircraft.
Some aircraft have up to 50% recirculation, so it is important to turn off the air recirculation quickly.
(2) While it is impossible to accurately predict the hazard level in most situations, try to avoid selecting extinguishers that could result in exposure to halocarbon vapors above the safe-use levels. Exposure may result in dizziness, impaired coordination, reduced mental acuity, and heart arrhythmias.
(3) Halocarbon agents also decompose when they contact open flames or hot surfaces. The decomposition products have a characteristic sharp, acrid odor, and an eye irritating effect, even in concentrations of only a few parts per million. See Annex A, Paragraph
1.5.1.2 and 5.7.1.2 of the standard in appendix 3, paragraph 11d of this AC, or the most current revision, for more detailed information on the effects of neat agent and hydrogen fluoride (HF) respectively, as well as further discussion of factors affecting the formation of thermal decomposition products.
c. Use Portable Protective Breathing Equipment (PBE). In compartments where extinguisher(s) are used that do not meet the sate-use guidance in this AC, flight crewmembers should use portable PBE, if available and/or as directed by FCOM procedures or AFM.
Unprotected personnel should not enter a protected space during or after agent discharge, until ventilated. Crewmembers should follow fire fighting procedures when using portable PBE. See paragraph 5b below for additional information on portable PBE use in cargo compartments.
d. Ventilate the Compartment.
(1) When you are reasonably sure the fire is extinguished, ventilate the compartment overboard at the highest possible rate allowed by established crew procedures for your particular aircraft to rid the cabin and flight deck of hazardous gases and smoke. Stay alert when increasing airflow, if the fire is not completely extinguished or smoldering, increasing airflow could promote fire growth.
(2) Small aircraft lack some of the safety advantages available to large transport category aircraft. Large aircraft with small volume occupied spaces (flight decks) have a forced ventilation system, availability of supplemental oxygen (quick donning oxygen masks), and a copilot available. Therefore, operators of small unpressurized aircraft should open a window, if at all possible.
3. How to Prevent Hypoxia in an Unpressurized Aircraft. You can avoid life-threatening hypoxia (low oxygen) hazards that may result from the discharged halocarbon agent displacing air in unpressurized aircraft, by following the descent, ventilation, and supplemental oxygen guidance below. See the report referenced in appendix 3, paragraph 7m of this AC for information on the development of the guidance below.
a. Extinguish Fire and Ventilate Cabin. As mentioned above, make sure the fire is completely extinguished. To rid the cabin and flight deck of hazardous gases and smoke, ventilate all unpressurized aircraft compartments overboard at the highest possible rate allowed by established crew procedures for your particular aircraft. If the fire is not completely extinguished, or a smoldering fire exists, increasing airflow could promote fire growth
b. Descend to Lower Altitudes. Immediately descend at the maximum safe rate to 8,000 ft. or to an altitude that is as low as practicable. Descending dilutes agent concentration, lowers exposure to agent and combustion gases, and increases oxygen concentration. We recommend descending regardless of the amount of agent used, the aircraft size, or ventilation rate. Aircraft with a maximum flying altitude of 12,500 ft. are protected from hypoxia, without the need for supplemental oxygen, by immediately descending as described above.
c. Use Supplemental Oxygen. Use of supplemental oxygen can prevent hypoxia.
However, if a supplemental diluter demand personal oxygen system at CPAs above 12,500 ft., a nasal cannula up to and including 18,000 ft CPA, or an oral-nasal mask between 18,000 ft. and 25,000 ft. CPA are used, the user will not be fully protected from hypoxia. This lack of protection is because the oxygen flow control for these systems is based on pressure altitude, not oxygen partial pressure.
(1) Occupants flying at altitudes above 12,500 ft. should immediately switch their masks or nasal cannula to the maximum flow of oxygen, if so equipped, to get additional protection during the time it would take to exchange the air in the compartment three times.
(2) Fingertip probe oxygen sensors should be used with oxygen systems on unpressurized aircraft with maximum flying altitudes above 12,500 ft. These devices provide user feedback on the effects of hypoxia after halocarbon agent discharge such that the wearer can increase the oxygen flow to their breathing device to compensate for the hypoxia.
(3) Unpressurized aircraft are allowed to use nasal cannula supplementary oxygen systems up to 18,000 ft. altitude. These systems provide no protection to a wearer when he or she breaths through the mouth, which can occur at times of stress.
4. What are the Guidelines on the Selection of Halocarbon Extinguishers?
Extinguisher Performance. Primary consideration in selecting a fire extinguisher should be performance, size, and weight (see appendix 4, paragraph 3 of this AC), hardware configuration, extinguisher throw range (see appendix 4, paragraph 1 of this AC), ease of use for novices, commercial availability of the agent, and environmental issues (ODP and GWP).
Special consideration needs to be made for cold temperature operation, as noted in chapter 3, paragraph 5b of this AC. Agent physical and chemical properties may also be considered.
Toxicity/Human Exposure. As mentioned previously, human exposure to halocarbon agents is a concern and needs to be addressed as noted in paragraph 2b above.
However, it is far less of a concern than the consequences of an unextinguished in-flight fire.
From a hazardous exposure perspective, you may elect to select a halocarbon hand extinguisher using the safe-use W/V guidance (based on perfect mixing) described below for your specific compartment size. Safe-use W/V guidance provides an objective scientific evaluation of the currently approved agents.
(1) The exposure hazard presented by the decomposition products of the agent may be considered when choosing a fire extinguisher for a particular installation.
(2) Safe-use W/V guidance for various air change times, assuming perfect mixing, is presented in appendix 4, paragraph 2 of this AC. The methodology used to develop the safe-use W/Vs of halocarbon agents and their blends was developed in the report referenced in appendix 3, paragraph 7m of this AC. The safe-use W/V guidance is based on the discharge of the largest extinguisher in a compartment at 70° F at the aircraft certificated CPA.
(3) These safe-use W/Vs may be used as general guidance and are based on perfect mixing gas concentration histories. This safe-use W/V guidance is not rigid, as there are many variables that can affect the agent concentration histories. Actual concentrations encountered by occupants may be significantly lower than would be encountered if there was perfect mixing depending on agent stratification, air distribution, air flow, and geometry of a particular aircraft/aircraft compartment and may be adjusted accordingly.
Agent stratification/localization within a compartment, as mentioned in paragraph 4b(3) above, will be addressed in a report to be published at the FAA Technical Center. This report will provide limited examples and the method to properly adjust the safe-use concentrations for those examples. See appendix 4, paragraph 2a(4) 17
(5) For unpressurized aircraft, you should consider safe-use guidance for the highest altitude for which the aircraft is certified.
(6) The cabin is considered and referred to as a compartment. The total charge weight of the largest extinguisher divided by the compartment volume should not exceed the safe-use W/V.
(7) In a pressurized aircraft (6000 to 8,000 ft CPA), the hypoxic hazard is minimal for the safe-use concentrations for the halocarbon agents in this AC. Immediate descent is not necessary. Pressurized aircraft benefit (increased oxygen and decreased agent concentrations) only from descent to altitudes below the CPA. The worst case oxygen equivalent CPA for pressurized aircraft using the safe-use W/V guidance provided in this AC is 10,000 ft at 2 minutes after discharge when 8,000 ft CPA is maintained. However, landing as quickly as possible is always recommended when an onboard fire is suspected.
c. Relative Agent Toxicity. You may want to consider the relative toxicity of extinguishers in Figure 1 below when selecting an extinguisher. Figure 1 shows the normalized toxicities of approved 5B:C extinguishers relative to the NOAEL-based toxicity of a 5B:C Halon 1211 extinguisher. These normalized toxicities are based on exposure to neat (un-decomposed) agent using 3 different measures: NOAEL, Safe Human Concentration and LOAEL.
Figure 1. Relative Toxicity of 5 B:C Halocarbon Extinguishers
1.3
• NOAEL Basis 1 • Safe Human Concentration Toxicity of 5 B:C Extinguishers .9 Basis Relative to Halon 1211 • LOAEL Basis 2
0.0 Halon 1211 Halon 1301 HCFC Blend B HFC-227 ea HFC-236 Agent
d. Minimum Safe Volume. Alternatively, you may consider minimum safe volumes to make your extinguisher selection. In this case, the minimum safe volume of one extinguisher is obtained by dividing that extinguisher's charge weight by the safe-use agent W/V for the appropriate altitude and ventilation (See appendix 4, paragraph 3 of this AC).