There are two (2) types of Asphyxiants:

1. Simple
2. Chemical also known as Systemic

These different types of asphyxiants behave differently and cause harm differently.

SIMPLE Asphyxiants displace the 20.8% Oxygen in the atmosphere.  These are NOT toxic or poisonous; they are called INERT gases.  The most famous SIMPLE Asphyxiant is Nitrogen (N2).  It is notoriously renowned as it has killed many workers inside and outside of confined spaces.  Since 2020, there have been 14 fatal accidents involving N2 that claimed 26 lives.  The most recent claimed Six (6) workers.

I have written several articles referencing code requirements when asphyxiants are used in the workplace. Most states (all but six) have adopted some version of the International Fire Code (IFC), which is an excellent baseline for designing systems handling these inert gases and the atmospheric monitoring systems REQUIRED in areas where these asphyxiants are stored, managed, and processed.

Creating a HAZ ATM takes very little of these gases (e.g., Oxygen-Deficient). Most of these simple asphyxiants have NO WARNING properties, meaning we can not smell, taste, hear, or feel their presence. A room/space at 20.8% O2 must only lose 1.3% of its O2 before we have an IDLH atmosphere. Without proper mechanical exhaust ventilation and/or an atmospheric monitoring system, workers can be overcome quickly.

NOTE: another simple asphyxiant gaining popularity without proper safeguards is Carbon Dioxide (CO2).  We are seeing Liquid Dewars of CO2 being used in the restaurant industry for soft drink machines and as a refrigerant in industrial refrigeration systems.

CHEMICAL/SYSTEMIC Asphyxiants work their harm differently.  The atmosphere could have adequate Oxygen levels, but once we inhale these chemical/systemic asphyxiants, the hemoglobin in our blood has an affinity for these gases over that of the Oxygen.  So these gases attach to our red blood cells/hemoglobin rather than the O2, and we "suffocate" in an adequate supply of O2. 

Carbon Monoxide is probably the most famous Chemical/Systemic asphyxiant.  When we hear of a death by "smoke inhalation," this was a CO-poisoning death.  When inhaled, carbon monoxide combines with hemoglobin (an iron-protein component of red blood cells), producing carboxyhemoglobin (COHb), greatly diminishing hemoglobin's oxygen-carrying capacity. Hemoglobin's binding affinity for carbon monoxide is 300 times greater than its affinity for oxygen. (Source: NIOSH)

Since 2022, there have been 20 fatal accidents involving CO, claiming 24 lives.

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