### September 20 , 2011 1 

## Significant New **Alternatives Policy Pr ogram**  **Fir e Extinguishing and Explosion Pr**  **evention Sector Risk Screen on Substitutes for Halon 1301**  **Total Flooding Systems in Normally Occupied or**  **Unoccupied Spaces Substitute:**  **N 2**  

### Towers **Inert Gas Generator Fire Suppr ession System**  **This risk screen does not contain**  **Clean Air Act (CAA) Confidential Business Information (CBI) and, therefore,**  **may be disclosed to the public.**  **1. I**  **ntroduction** Ozone - depleting substances (ODS) are being phased out of production in respons e to a series of diplomatic and legislative efforts that have taken place over the past decade, including the Montreal Protocol and the Clean Air Act Amendments of 1990 (CAAA). The U.S. Environmental Protection Agency (EPA), as authorized by

Section 612 o f the CAAA, runs the Significant New Alternatives Policy (SNAP) Program, which identifies acceptable and unacceptable substitutes for ODS in specific end -uses based on assessment of their health and environmental impacts. EPA’s decision on the acceptabili ty of a substitute is based largely on the findings of a screening assessment of potential human health and environmental risks posed by the substitute in specific applications. EPA has already screened a large number of substitutes in many end

– use applic ations within all of the major ODS -using sectors, including refrigeration and air conditioning, solvent cleaning, foam blowing, aerosols, fire suppression, adhesives, coatings and inks, and sterilization. The results of these risk screens are presented in a series of Background Documents that are available in EPA's docket. The purpose of this risk screen is to supplement EPA’s Background Document on the fire suppression and explosion protection sector (EPA 1994) (hereinafter referred to as th e Background Document). This risk screen discusses potential human health and environmental risks posed by the N 2 Towers Inert Gas Generator Fire Suppression System (N 2 Towers System) when used as a total flooding agent in normally occupied or unoccupied spaces as a replacement for Halon 1301 . The N 2 Towers System is an inert gas system designed for total flooding applications for fires in normally occupied or unoccupied spaces. The nitrogen gas generating propellant grains are formed into purple colored discs, each w ith a diameter of 39 mm and a height of 15 mm. Each disc contains 19 perforations, with an inside diameter of 2.5 mm. Each ten - inch N 2 g enerator unit contains 96 propellant grain disc s in a total of 14 layers: seven discs per layer for the 12 middle layer s and six discs per layer for the top and bottom layers. Depending on the fire suppression requirement, s everal generators may be stacked inside an N 2 Tower in a room , or a single generator may be bracketed inside an armo red vehicle. Upon activation, the substitute undergoes the following chemical reaction: 4NaN 3 + Fe 2 O 3 → 2Na2 O.FeO + 6N 2

### September 20 , 2011 2 The nitrogen is discharged into the space and the remainder of the activation products are filtered and contained inside the N 2 g enerator, where moisture is absorbed from the ambient air, neutralizing the sodium hydroxide until all that is left inside the g enerator is a burnt propellant sinter. The sinter is contained within the filter inside the sealed N 2 g enerator until the entire unit is disposed of at an appropriate disposal facility . The largest N 2 g enerator, 24” long by 7” in diame ter, can discharge up to 6.9 pounds of nitrogen gas in approximately 100 milliseconds. The submitter will use this size for the existing stockpile of grains. 1 Each 24” long by 6” diameter generator can protect up to 400 cubic feet of volume , and multiple g enerators may be combined to protect a single space (N 2 Towers Inc. , 2009 , 2010 a, 2010b ) . Table 1 provides the composition of propellant grains contained in N 2 Tower S ys tem s , prior to activation . 

### Table **1 .**  **Composition of N**  **2** 

### Towers **Component Chemical Form**  **ula CAS No.**  **Weight Percent** Sodium Azide (s) NaN 3 26628 - 22 - 8 50 - 70 Ferric Oxide Fe 2 O 3 1309 - 37 - 1 20 - 35 Graphite C 7782 - 42 - 5 2 - 7 Bentonite Al 2 O 3 .4(SiO 2 ).H 2 O 1302 - 78 - 9 0 - 5 Sodium Nitrate NaNO 3 7631 - 9 - 4 0 - 5 Potassium Perchlorate KClO 4 7778 - 74 - 7 0 - 3 Amorp hous Silica SiO 2 112926 - 00 - 8 0 - 2 Source: N2 Towers Inc. ( 2009 ) Section 2 of this risk screen summarizes the results of the risk screen for the proposed substitutes listed in Table 1. The remainder of the risk screen is organized into the following secti ons:

 Section 3 : Atmospheric Assessment ;  Section 4 : Occupational Exposure Assessment;  Section 5 : End - Use Exposure Assessment ;  Section 6 : G eneral Population E xposure Assessment ;  Section 7: Volatile Organic Compound Assessment; and  Section 8: References . 

### 2. **Summary**

**of Results** The N 2 Towers System is recommended for SNAP approval as a total flooding device in normally occupied or unoccupied spaces for fire suppression . EPA recommends that Section VIII of the Occupational Safety

& Health Administration ( OSHA) Technical Manual be consulted for information on selecting the appropriate ty pes of Personal Protective Equipment ( PPE ) recommended (OSHA 1999) . The risk screen indicates that the use of the proposed substitute in normally occupied or unoccupied spa ces will be less harmful to the atmosphere than the continued use of Halon 1301. Additionally, the risk to the general population is expected to be below levels of concern for non - cancer risks . For applications of this

1 In evaluating the occupation exposures during manufacture, this risk screen is limited to the existing stockpile of propellant grains that have already been manufactured . According to the submitter, the quantity of propellant grains in the existing stockpile can be used to manufacture approximately 20,000 N 2 generators. Any future manufacture of N2 Towers Systems which requires production/manufacture of propellant grains will require additional EPA screening for approval under the SNAP program.

### September 20 , 2011 3 and all other water mist/inert gas fire suppression equipment, EPA recommends that the latest editions of National Fire Protection Agency (NFPA) Standards 750 and 2001 be followed. 

### 3. **A tmospheric**  **As sessment**  This section presents an assessment of the potential risks to atmospheric integrity posed by the use of the N 2 Towers System as a total flooding system in normally occupied or unoccupied areas . The constituents of N 2 Towers Systems are solids before use and therefore have zero ozone depleting potential (ODP) and global warming potential (GWP) Further, a s indicated in Table 2 , the ODP of each of the post - activation constituent s of N 2 Towers is zero and m ost of the post - activation constituents also have zero GWP . The GWP and ODP of the compounds in N 2 Towers are well below the GWPs of previously SNAP - approved fire - suppression agents (e.g. HFCs and other high - GWP fluids). Accordingly , use of the N 2 Towers System is not expected to pose any significant adverse atmospheric impacts. 

### Table **2 . ODP**  **and 100**  **- Year GWP of**  **the N**  **2** 

### Towers **System Cons**  **tituents**

**Constituent ODP**  **100 -**  **Year GWP** N 2 0 0 CO 0 3 a CO 2 0 1 a Based on indirect radiative effects, Fuglestvedt et al. (1996) 

### 4 **. Occupational Exposure**  **As sessment**  The potential for personnel exposure during manufacture , installation, and maintenance are examined in this section. According to information provided in the N 2 Towers SNAP application , all N 2 Tower S ys tems will be fabricated using an existing stockpile of TRW sodium azide propellant grains. The stockpile of grains is stored in an airtight moisture proof bag made of aluminum foil and are not opened until they are placed inside the N 2 generator. Thus, any exposure during manufacture will be limited to propellant grain loading into the N 2 g enerator. 2 According to the submitter, all loading of t he grains will be performed using a down draft loading table. Due to the inhalation , oral and dermal toxicity of sodium azide , all employees involved in propellant loading should wear appropriate PPE, such as protective clothing, gloves, goggles, and respiratory protection , as described in the compound’s MSDS . It is expected that level B of the levels of protection presented in the OSHA Technical Manual (OSHA 1999) will afford the appropriate protection. In the case of an accidental spill, workers should immediately vacate the premises and follow the first aid guidelines listed in the MSDS. Because of the minimal chance of worker exposure to the chemicals during the manufacturing process, the use of these exposure controls and adherence to the appropriate occupational safety guidelines as mentioned above, are sufficient to ensure that the manufacture of N 2 Towers Systems does not pos e a risk to human health.

2 According to the submitter, all grains will be placed inside the N 2 g enerators by UTeC technicians. Once loaded, end caps are sealed and screwed into place on the N2 generators. After sealing, the generator is safe for storage and shipping (N2 Towers, Inc. 2010b)

### September 20 , 2011 4 During installation or maintenance of an N 2 Towers System , inadvertent discharge of the substitute may occur. According to the submitter, during installation and maintenance, no exposures to the propellant are expected to occur as the generator body is a sealed steel casing with propellant grains contained therein . However, in the event of inadvertent discharge , oxygen concentration would be expected to decline over time. T o ensure that exposures are minimized, it is recommended that N 2 Towers Systems provide safety training for technicians to minimize the occurrence of an inadvertent discharge. T raining should also be provided regarding egress from the space should such a discharge occur . 

### 5 **. End**  **- Use Exposure A**  **ssessment** The primary

health concern for agents containing or releasing inert gases, including nitrogen gas, is asphy xiation due to reduce d oxygen concentrations . To determine whether asphy xiation could occur at the end -use, the N 2 Towers System design parameters were analy zed. N 2 Towers Inc. conducted fire suppression tests to measure the oxygen , carbon monoxide, carbon dioxide and particu lates concentrations at the time of flame suppression Ta ble 3 presents the calculated design concentrations based on the results of N 2 Tower s ’ fire tes ting and a conservative estimate provided by the submitter. To determine the minimum design concentration for the N 2 Towers System , a 30 percent safety factor was applied to the extinguishing concentrations , in accordance with NFPA 2001 Guidelines (NFPA, 2007). 

### Table **3 .**  **Summary of N**  **2** 

### Towers Inc. **’s Fire Tests and**  **Calculated Minimum Design**  **Concentration s**  **Test Extinguishing Concentration**  **a Design Concentration (% N**  **2 /% air**  **(v/v)) c,**  **d % O**  **2 /% air**  **(v/v) % N**  **2 /% air** 

**(v/v) c**  **% CO/% air**

**(v/v) b**  1 16.2 **b** 22.7 215.6 29.5 3 16.0 **b** 23.6 288 30.7 4 15.8 **b** 24.6 299 32.0 5 15.8 **b** 24.6 339 32.0 **NA e**  **14.5** e **30.8 NA**  **40.0** a Source: N 2 Towers Inc. ( 2009 and 2010b )
. b O 2 and CO levels are experimentally measured. c N 2 levels are calculated based on experimentally measured O 2 levels. These values are exclusive of atmospheric nitrogen, i.e. represent the concentration of ni trogen from the N 2 Towers System only in the air. d D esign concentration s were estimated by applying a 30 percent safety factor to the extinguishing concentrations e O 2 level provided by submitter as a conservative estimate. According to the submitter, the N 2 Towers System creates wind vorticity and lowers the oxygen levels of a space down to approximately 14.5 % oxygen per volume. Based on the conservative estimate of oxygen levels , the nitrogen extinguishing concentration was calculated to be 30.8 perc ent and the design concentration to be 40.0 percent. Because N 2 Towers Systems are designed to ensure that the oxygen concentration in any protected space will not fall below 12 percent over the discharge period, N 2 Towers is considered safe for fires in normally occupied or normally

unoccupied spaces for inert gases.

### September 20 , 2011 5 **6. G**  **eneral Population Exposure As**  **sessment** Given the large natural quantities of nitrogen and water in the atmosphere, it is unlikely that an accidental release of N 2 Towers will affect the average atmospheric concentrations of these gases. As such , N 2 Towers is not believed to pose a toxicity threat to the general population. 

### 7 **. Volatile Organic Compound**  **As sessment**  The constituents of the N 2 Towers are not considered VOCs fo r purposes of local air quality . 

### 8 **. References**  EPA. 1994. Risk Screen on the Use of Substitutes for Class I Ozone - Depleting Substances: Fire Suppression and Explosion Protection (Halon Substitutes). Stratospheric Protection Division. March 1994. Fuglestvedt, J.S., I.S.A. Isaksen and W. - C. Wang, 1996: Estimates of indirect global warming potentials for CH 4 , CO, and NO x . Clim. Change, 34, 405 - 437. N 2 Towers, Inc. 2009. SNAP Submission to EPA for N 2 Towers. December 22, 2009. N 2 Towers, Inc. 2010 a. http://n2towers.com/ Accessed March 22, 2010. N 2 Towers, Inc. 2010 b . Response to Incomplete SNAP Submission for N 2 Towers. March 10, 2010. N FPA, 2007 . NFPA 2001: Standard on Clean Agent Fire Extinguishing Sy stems. 2008 Edition. Available at: http://www.nfpa.org/freecodes/free_access_document.asp OSHA. 1999. OSHA Technical Manual. Department of Labor. Occupational Safety & Health Administration. January

20, 1999. Available online at : http://www.osha.gov/dts/osta/otm/otm_toc.html