Table 1.

Characteristics of H₂ and CO related to safety issues

	H2	CO
Flammability range in air	4.0–75.0 vol%a	12.5–74.2 vol%b
Auto‐ignition temperature in air	585°Cc	605°Cb
Specific gravity (compared to air at 20°C, 1 atm)	0.07a	0.97b
Permissible exposure limit (PEL)	n. a.	35 ppmb
Recommended exposure limit (REL)	n. a.	50 ppmb
Immediately dangerous to life or health value (IDLH)	n. a.	1200 ppmb

n. a. not available

^aZabetakis (1965).

^bNIOSH (2016).

^cWhite et al. (2006).