Knockdown Pattern (H2S)
Definition
The scene distribution of multiple H2S victims clustered at the entrance or access point of a confined space, as first responders and would-be rescuers are overcome in sequence. Pathognomonic for a confined-space H2S event.
- Gas involved
- Hydrogen sulphide
- Pattern
- Multiple victims clustered near entrance or access point
- Mechanism
- Sequential collapse of victims and would-be rescuers
- Diagnostic value
- Pathognomonic for a confined-space H2S event
Common questions
Why do rescuers so often become additional victims in an H2S knockdown scene?+
Hydrogen sulphide can cause near-instant loss of consciousness at high concentration, so an untrained person entering to help a collapsed worker is overcome within seconds without any warning odor, since H2S also rapidly deadens the sense of smell at dangerous levels, adding victims in sequence near the entry point.
How does a knockdown pattern help distinguish H2S exposure from another toxic gas incident?+
The specific clustering of victims at an access point, combined with scene context such as a sewer, tank, or manure pit and any characteristic rotten-egg odor reported before collapse, points investigators toward H2S over other asphyxiants like carbon monoxide, which typically show a more diffuse victim distribution.
Related terms
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- Cherry-Red Livor Mortis
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- Co-Oximetry
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- Cytochrome C Oxidase (Complex IV)
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- GC-FID
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- Sulphhaemoglobin (SHb)
- A modified haemoglobin species in which one or more pyrrole rings is sulphonated by reaction with hydrogen sulphide. Produces green-brown blood and...