Mechanism: suicide, accidental, homicide
The presence of helium can often be demonstrated if specimens are collected properly. It is possible to miss the presence of helium if the specimens are collected improperly.
Specimens to consider:
(1) collection of air from the lungs using a large gas syringe with immediate transfer to a PET/aluminum/EVA multilayer gas sampling foil bag
(2) tissue samples placed in a 10 mL headspace vial and immediately sealed with a silicone/PTFE seal and magnetic crimpcap
Lung is the preferred specimen. Brain, heart blood and other samples may be positive but often at low concentrations. Tissue samples should be sample as soon as possible after the body is entered.
Method of analysis: headspace gas chromatography-thermal conductivity detection (HS-GC/TCD) with nitrogen as carrier gas
Tissue sample preparation: head space vials incubated at 70°C in the oven of the headspace sampler for 20 minutes
Helium can be detected in properly collected specimens for several days after death.
An attempt at resuscitation may allow helium within the lung to be lost.
Death determination requires assessment of the entire scene. The presence of helium can support the diagnosis.
