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|  MIL-T-62531(AT)
APPENDIX A
Verification Lessons Learned
3.4.6.1 Toxic gas exposure.
3.4.6.1.1 Carbon monoxide. Operating and maintenance personnel shall not be exposed to
concentrations of CO in excess of values which will result in COHb levels in their blood greater
than 10% in accordance with MIL-STD-1472C. The equation used to estimate the percent
COHb blood levels will be in accordance with MIL-HDBK-759A using work stress level 4 for
weapons firing and work stress level 3 for all other mission activities.
Rationale
The design and installation of the engine and heater exhaust systems must be leakproof to
prevent the entry of noxious substances into an enclosed vehicle crew compartment. CO is
particularly dangerous in that it is odorless, colorless and tasteless and is not ordinarily
detectable by the human senses. In sufficient concentrations, the noxious substances may
incapacitate personnel or reduce substantially their performance through eye irritation, nausea,
reduced mental alertness, and even unconsciousness.
Guidance
All connections of the exhaust systems shall be symmetrical to assure a positive leakproof fit.
Exhaust system clamps should be of the required size and shall be torqued to the specification
requirements.
4.4.6.1.2 Other toxic gases. To determine conformance to 3.4.6.1.2, concentration of
nitrogen oxides, ammonia, nitric oxide and sulfur dioxide shall be limited to those values
specified by ACGIH.
Rationale
The presence of either carbon monoxide or ammonia in excessive concentration has been
known to reduce the effectiveness of personnel. It is obvious that concentrations of such toxic
agents should not be permitted to build up beyond their tolerable limits in personnel
compartments.
Guidance
The vehicle shall be tested for concentration of CO not to exceed 50 parts per million (ppm);
for ammonia (NH3) 5.0 ppm; and for nitrogen dioxide (NO2) 5.0 ppm. The NO2 is a ceiling
value which should not be exceeded at any time. Careful consideration should be given in
designing vehicle compartments to provide sufficient ventilation to maintain the concentration of
gases, vapors and fumes below an irritating and nauseating level.
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