Flammability testing heat release

Modified Flammability Tests. A number of smoke tests exist in which the smoke produced by a flammability or heat release test is determined using photocell light systems positioned in the smoke streams. 

PAEK materials show extremely low flammability, achieving UL V-0 classifications with a wall thickness as low as 0.8 mm without the need for fillers or other additives. It is reported that at least one PAEK (PEEKK) is able to meet the OSU Test for heat release which has been required by the Federal Aviation Administration since 1990—a requirement no longer satisfied by many of the materials used in aircraft construction. 

The purpose of bench-scale reaction-to-fire tests is to measure the flammability characteristics of materials, i.e., ease of ignition, flame spread propensity, heat release, and production of smoke and toxic combustion products. Some tests are designed to measure only one of these characteristics. Other tests are more sophisticated and can be used to measure several characteristics at the same time. 

The thermal combustion properties measured in the test are related to the flammability characteristics of the material.5155 For example, the heat release temperature from method A approximates the surface temperature at ignition (Section 14.3.2.1). The net calorific value from method B approximates the net heat of combustion measured in an oxygen bomb calorimeter. 

Candidate polymers were screened for flammability using microscale MCC according to a standard method [18], In the test, a 3-5 mg sample is heated at a rate of 1 K/s from ambient temperature to 850°C. The pyrolysis gases are purged from the sample chamber with nitrogen, mixed with excess oxygen, and combusted at 900°C. Heat released by combustion of the pyrolysis gases is calculated... 

Requirements for upholstered furniture flammability exist in various states, including California, based on California Technical Bulletin 133 (CA TB 133),91 which was also made into a consensus standard by ASTM committee E05 as ASTM E 1537.92 The gas burner used as the ignition source in CA TB 133 is a square-shaped burner that applies propane gas for 80s at a flow rate of 13L/min. The test is severe enough that it can usually not be met, unless the foam contained in the upholstered furniture item is flame-retarded. The pass/fail criteria are a peak heat release rate of 80 kW and a total heat released that does not exceed 25 MJ over the first 10 min of the test. In California, moreover, all foam contained within upholstered furniture must be flame-retarded to comply with CA TB 117. Moreover, the IFC and NFPA 101 both have parallel requirements to those discussed earlier for mattresses. In other words, the 2006 editions of both the codes contain requirements that upholstered furniture items in health care occupancies as well as detention and correctional occupancies that are not sprinklered must comply with a peak heat release rate of 250kW and a total heat release of no more than 40 MJ in the first 5 min of the test, when tested to ASTM E 1537 (or CA TB 133). However, the 2007 edition of the IFC and the 2009 edition of NFPA 101 lowered these values to 80 kW and 25 MJ over 10 min. Finally, the IFC 2007 added college and university dormitories to the list and eliminated the sprinkler exception for detention occupancies. 

Subsequently, the ignition temperature and the HRC parameter can be determined and used to compare PCFC data with data from other test methods. The HRC is defined as the ratio of the heat release rate and the heating rate. The peak heat release rates determined in cone calorimeter experiments correlate well with peak HRC data from PCFC experiments. In terms of other tests, results from the LOI (ASTM D 2863) test method exhibit a reciprocal correlation with HRC values, while HRC can also be a rough indicator for UL 94 ratings. In approximate terms, it has been said that HRC results can classify materials into three ranges of material flammability, as follows ... 

Bourbigot et al.85 at Lille have used poly(vinylsilsesquioxane) (POSS) in PP (110 wt%) to melt spin filaments, which were then knitted into fabrics. POSS was thermally stable and no degradation was detected in the processing conditions. They have tested the flammability of the fabrics using cone calorimetry. POSS presence had minimal effect on peak heat and total heat release values of PP fabric, but delayed the TTI. This behavior of POSS is opposite to that of layered silicates, which have minimal effect on TTI, but reduce PHRR. Authors claim that POSS does not act as a FR but only as a heat stabilizer via a decrease of the ignitability. 

Cone calorimetry according to the ASTM E1354138 or ISO 5660139 standards are commonly used in the laboratory to screen flammability of materials by measuring heat release characteristics of the compound.116140 This device is similar to FPA but does not have the versatility of FPA. The cone calorimeter can determine the ignitability, heat release rates, effective heat of combustion, visible smoke, and C02 and CO development of cable materials. This test has been used extensively for wire and cable material evaluation. The microscale combustion calorimeter (MCC), also known as pyrolysis combustion flow calorimeter (PCFC), was recently introduced to the industry for screening heat release characteristics of FR materials.141142 This device only requires milligram quantities of test specimen to measure the heat release capacity (maximum heat release potential). Cone calorimetry and MCC have been used in product development for flammability screening of wire and cable compounds.118... 

FIGURE 26.4 Probability for flame spread versus heat release capacity of compounds. (Cogen, J.M. et al., Correlations between pyrolysis combustion flow calorimetry and conventional flammability tests with halogen free flame retardant polyolefin compounds, Fire Mater., 2009, 33, 33-50.)... 

FIGURE 26.6 Relationship between FIGRA and THR measured in MCC (i.e., PCFC). FIGRA = PHRR/ TTPHRR, FPI = TTI/PHRR, where PHRR is peak heat release rate, TTPHRR is time to peak heat release rate, and TTI is time to ignition. (Based on Lin, T.S. et al., Correlations between microscale combustion calorimetry and conventional flammability tests for flame retardant wire and cable compounds, in Proceedings of 56th International Wire and Cable Symposium, 2007, pp. 176-185.)... 

A micro-scale combustion calorimetric method test has been developed by Walter and Lyon, which involves pyrolysis and combustion calorimetry of the volatile products [12]. Using this technique, the heat release capacity can be obtained. The heat release capacity is a material parameter and has been used to correlate polymer structures with flammability [13]. 

No differences in flammability characteristics between the 0.1% Cu20-treated and untreated flexible polyurethane foam were observed. These characteristics were examined to assure that the positive effect on toxicity was not contradicted by negative effects on the flammability properties. The flammability characteristics examined were (1) ignitability in three systems (the NIST Cup Furnace Smoke Toxicity method, the Cone Calorimeter, and Lateral Ignition and Flame Spread Test (LIFT)), (2) heat release rates under small-scale (Cone Calorimeter) and medium-scale (furniture calorimeter) conditions, (3) heats of combustion under small-scale (Cone Calorimeter) and medium-scale (furniture calorimeter) conditions, (4) CO/CO2 ratios under small-scale (Cone Calorimeter) and medium-scale (furniture calorimeter) conditions, (5) smoke obscuration (Cone Calorimeter), and (6) rate of flame spread (LIFT). 

The burn results for polymers 15 and 19 show that the polymers are inherently flame retardant with low base flammability (Table 4). The polymer dripped but did not ignite the cotton when it was subjected to the UL-94 flame test, and with the addition of 1 wt% PTFE, it did not drip. The PCFC results show that these polymers have a high heat release capacity when compared with the BPC carbonates and aryl ethers, but it is still significantly less than that of the base commodity polymers, such as polyethylene or polystyrene (Table 5). 

Applications. In this test, the flammability of materials is considered as a function of the heat release rate and critical ignition energy. Flammability is inversely proportional to ignition energy and directly proportional to heat released. ... 

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