Agenda for the presentation: (1) Brief background of ISO 16697 (a) Reasons for the approach (b) Stated intent for this International Technical Specification (2) Evolution of initial considerations for the ISO approach (3) Discussion and recommendatio

Beeson, Harold D.

Hirsch, David B.

NASA Technical Reports Server

Remarks on Flammability 
Testing of Aerospace 
Materials
David B. Hirsch
Harold D. Beeson
NASA/JAXA Technical Interchange Meeting
NASA WSTF
Las Cruces, NM USA
March 8, 2013
https://ntrs.nasa.gov/search.jsp?R=20130011021 2019-08-31T00:22:35+00:00Z
Agenda
• Brief background of ISO 16697
– Reasons for the approach
– Stated intent for this International Technical Specification
• Evolution of initial considerations for the ISO approach
• Discussion and recommendations
•
Brief Background of ISO 16697 
• NASA STD 6001 Tests 1 and 4 data correlation issues.
• Flammability threshold approach – implemented in 2011 
as ISO Technical Specification 16697. 
• The method allows to determine the self-extinguishment 
limits of one parameter (oxygen concentration, or total 
pressure, or microgravity level, etc.) while keeping other 
parameters constant.
• It is important to note that with the exception of the 
pass/fail test logic, ISO 16697 follows NASA STD 6001 
Test 1 (or Test 4).  
Why the ISO 16697 Approach (besides the data 
correlation issues)
• Large NASA STD 6001 flammability database with live 
actual aerospace applications (Space Shuttle at the time, 
in 2002; ISS).
• Very little (if any) existing micro- or reduced-gravity 
flammability threshold data at the time.
• Perceived need for enhanced precision and accuracy 
mostly for immediate research applications related to 
data correlation.
Stated Intent of ISO 16697
• The intent is being called out in the Introduction Section
• “To bring to the attention of International Aerospace Community the 
importance of correlating laboratory test data with real-life space 
systems applications.” 
• It is emphasized that “The method presented is just one of 
possibilities that are believed will lead to better understanding the 
applicability of laboratory aerospace materials flammability test 
data”.  
• “International feedback on improving the proposed method, as well 
as suggestions for correlating other laboratory aerospace test data 
with real-life applications relevant to space systems are being 
sought.”
Evolution of Initial Considerations  for the 
ISO 16697 Approach  
• On-going work on correlating ground flammability test data and data 
in micro- and reduced-gravity based on flammability threshold.
• There are experimental constrains in spacecraft and ground 
microgravity flammability testing. By necessity, this work has to be 
conducted with samples of different configurations, ignition mode, 
perhaps pass/fail criteria than the ones used by NASA STD 6001.
• Current correlations (A to B to C) are more complex (i.e. correlate 
NASA STD 6001 configuration to spacecraft test configuration to 
spacecraft microgravity environment) Increased uncertainty 
associates this complexity.
Evolution of Initial Considerations: Phenomenology 
Related to Precision and Accuracy
• Statistical uncertainty and phenomenological uncertainty analyzed 
statistically.
• Ex. Uncertainties associated with attribute  (pass/fail) data: Binomial 
cumulative probability P of k samples failing in n tests for a material 
with a p failure probability.
Probability of at least one 
sample failing under a set 
of conditions (%) 
Probability of no failures observed in 
n tests under the same conditions (%)
     n = 3            5           10           20        
  
10 73              59         35           12
5 86              77         60            36
1 97              95         90            82
  
 
Evolution of Initial Considerations: Observations on 
Phenomenological Uncertainty
• ISO 16697 appears to provide high precision data (i.e considering data 
linearity related to pressure effects on the oxygen concentration 
threshold [1]).
• The range between the highest oxygen concentration at which all samples 
tested (5) pass and the oxygen concentration at which 50% of samples 
pass is relatively small (mostly 1 to 3% for materials with MOC’s up to 30%);  
This range appears to increase with increasing MOC’s;
• It appears that the curve describing the dependence of probability of failure 
with oxygen concentration is abrupt (close to verticality); i.e the probability 
of a sixth sample failing upon a series of five samples passing is relatively 
low.  Consequently, it is possible that an acceptable accuracy may be 
achievable with a less rigorous statistical approach.
Other Observations
• An earlier study [2] compared the oxygen concentrations at which 
50% of samples passed (the oxygen limiting index as accepted by 
the combustion community) for two methods.
• One method consisted of an upward flammability test conducted in a 
LOI apparatus in flowing environments (4 cm/s surface velocity);  the 
second method consisted of a modified NASA STD 6001 test 
conducted in a quiescent environment in a 1400-L chamber.  The 
test logic of NASA STD 6001 has been modified to allow evaluation 
of the 50% passing point.  
• The data indicates that for most materials tested (PMMA, HDPE, 
POM, PA, PU) the 50% passing points were nearly identical. 
Discussion and Recommendations
• The flammability threshold testing approach can provide data which 
allows comparing ground test data with data in spacecraft 
environments; additionally, the data obtained is applicable for 
various spacecraft environments and will not require extensive 
re-testing if the design parameters of new spacecraft are changed.
• The specific version for a ground standard test method should be 
further investigated considering the micro and reduced-gravity 
combustion research needs and approaches, an acceptable 
compromise on testing cost vs data accuracy, etc.  


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