Downloaded from https://www.everyspec.com MIL-STD-2031(SH) 40.4.S Alternate procedure. If the trial run shows that the average temperature in the exposure chamber will exceed 40 (105 “F), the electrical power to the furnace may be cut when the sample is completely degraded. In this case, allhough the furnace is shut off before the 30 minuw exposure is completed, ~hc exposure chamber shaii remain closed and the animals si~all receive a fuli 30 minute exposure. ‘Ike length of time required to degrade a sampie that produces CO shall be determined by monitoring the increase of CO concentration.
For those materials that do not produce CO, another degradation product shail be analytically monitored. When the concentration of the monitored gas reaches a steady state for 2 minutes, the heater shall be turned off. 40.5 Analytical tests. Two analytical experiments without animals shall be conducted first under separate non-flaming, flaming, or non-flaming/flaming transition conditions to determine the concentrations of CO, C02, and HCN that would be generated and the 02 depletion levels from different mass loadings of each material.
If the trial run does not produce an exmive exposure temperature and, for non-flaming teats, the sample does not ignite, then the trial run may be considered one of the two analytical tests. These species concentrations shall be used to predict the LC50 value for the selcctcd combustion mode. The animals shall be exposed to the mass of material that is equivalent to 80 percent of this predicted value. 403.1 Test initiation. To initiate the anaiytieai experiments, the weidwd sam~ies shall be placed in the preheated, preweighed cup in the furnace and the door of the exposure chamber immediately cIosed. PIa~ment of the sample into the furnace shall designate the starting time of the exposure.
lle matet-id shall h allowed to decom&ae for 30 minutes. 40.6 N-GoB Model prediction for IXm mass of material. l-king the gas ~-ntratiom obtained during the analytical test+ calculate the N-Gas Model .prudicticms with the Mud ~uations. These equations have been empirically derived to predict when 50 pereent of the animals should die either within the 30 minute exposure or within a 24 hour post~ure period. This oeeum when the equation is approximately equal to L These N-Gas Model equations are based on NIST studies of the toxicological interactions of two to four of these gases. The current model equations do not predict post-exposure deaths ocwrring after 24 hours.
Based on anticipated material composition, use one of the three equations listed below to determine the material mass loading that produces the LC~ value, that is when the equation is approximately equal to 1. To determine the amount of material that shall be used in the animal exposure tests, take 80 pereent of the material mass calculated for the LCW value. (1) For CO and HCN: [CO~CnCO + [HCNJ/LC#CN S= 1 A 0.2 where the brackets indicate the actual concentration of the specified gases; the LCW value of Co is based on 30 minute exposures and is 6600 p/m and the ~ value of HCN is 160 @m for 30 minute exposures or 110 phn for 30 minute exposures plus 24 hour pcmt-exposure deaths.
(2) For CO, HCN, and C02: m[COJ/([C02]-b) + [HCN)/LC$oHCN = 1 * 0.2 44