Aerospace Toxicology Overview: Aerial Application and Cabin Air Quality - Reviews of Environmental Contamination and Toxicology - page 29

For example, polymers, such as polyethylene produces CO and CO 2 ; Nylon 6/6
produces CO, HCN, and CO 2 ; polyamide produces CO, HCN, and CO 2 ; polystyrene
produces CO, CO 2 , and benzene; chlorinated polyethylene produces CO, CO 2 , and
hydrogen chloride; and polysulfone produces CO, CO 2 , and sulfur dioxide (Fenner
1975 ; Harper 1975 ; Sanders et al. 1991, 1992 ). Of these, CO and HCN are two
primary toxic gases present in smoke (Chaturvedi 1995 ; Chaturvedi and Sanders
1995, 1996 ; Sanders and Chaturvedi 1994 ).
Carbonaceous compounds produce CO and CO 2 upon burning, and nitrogenous
compounds also produce HCN (Chaturvedi 1995 ; Sanders et al. 1991, 1992 ;
Chaturvedi and Sanders 1995, 1996 ). Because the aircraft structure is composed of
a variety of carbon- and nitrogen-containing polymeric materials, there is strong
potential for the generated smoke to be rich in CO and HCN. In the absence of ire,
the presence of CO in the interior of the aircraft would suggest a malfunctioning of
the heating/exhaust systems. Since aviation fuel is primarily a mixture of non-nitro-
gen-containing hydrocarbons, aircraft engine exhaust would contain a negligible
amount of HCN (Chaturvedi et al. 2001 ).
Exposure of aircraft occupants to CO and HCN can be monitored by analyzing
for these gases in the blood as carboxyhemoglobin (COHb) or the cyanide ion
(CN − ). Analytical methods for measuring COHb and CN − are mentioned in an over-
view (Chaturvedi 2009, 2010a ) and in an international standard (ISO International
Standard 2008 ). Those analytical methods are summarized herein.
For COHb:
1. Whole-blood oximetry by simultaneous differential visible spectrometry at vari-
ous characteristic wavelengths (AVOXimeter 2001 ; CO-Oximeter 1978 ; Freireich
et al. 1975 ).
2. Reduction of palladium chloride to palladium by releasing CO from COHb in
blood by sulfuric acid and measuring absorbance at 278 nm of the remaining unre-
acted palladium chloride solution (Williams 1970, 1975 ; Williams et al. 1960 ).
3. Visible spectrophotometry by hemolyzing red blood cells by ammonium hydrox-
ide, treating the hemolysate with sodium dithionite to reduce methemoglobin
(MetHb) and oxyhemoglobin (OxyHb) to deoxyhemoglobin (HHb), and measur-
ing absorbance at 540 nm, a wavelength of maximum absorbance for COHb, and
at 579 nm, a wavelength at which the spectra of various species of HHb have the
same absorbance (Blanke 1976a ; Canield et al. 1998, 1999 ; Douglas 1962 ;
Sanderson et al. 1978 ; Tietz and Fiereck 1973 ; Winek and Prex 1981 ). A ratio of
absorbance values at 540 nm and 579 nm is used to determine %COHb in the
specimen, with the help of a calibration curve.
4. Visible spectrophotometry by saturating Part 1 of three equal parts of blood
hemolysate with CO, and of Part 2 with oxygen (Part 3 was not treated with any
gas), adding sodium dithionite to all the three parts to reduce MetHb and OxyHb
to HHb, and determining ratios of the absorbance values of the solutions at 540
and 579 nm to ind out %COHb in the specimen by using a mathematical rela-
tionship (Canield et al. 1998, 1999 ; Rodkey et al. 1979 ; Sanderson et al. 1978 ;
Uges 2004 ; Widdop 2002 ; Winek and Prex 1981 ).