As we have discussed, the latest revisions of the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) has a new criterion for categorization of flammable gases. The GHS now has sub-categories of CAT 1 Flammable Gases: 1A and 1B. CAT 1B flammable gases have a fundamental burning velocity of less than 10 cm/s. Never have I dealt with burning velocities to establish a degree of hazard for a flammable gas or vapor, but in all fairness, 10 cm/sec is really SLOW. How slow?
Having played football for many years, I like to do my comparisons to a 40-yard dash. A world-class athlete can run a 40-yard dash under 5 seconds, which is covering 8 yards per second. This is also around 16 mph. So have fast would I run the 40 if I was running 10 cm/sec?
10 cm = 3.9 inches
10 cm/sec = 0.1094 yard/sec
10 cm/sec is also 0.22 mph
40 yards = 3,657 cm
A world-class athlete can run a 40-yard dash under 5 seconds, which is covering 8 yards per second.
A flame front traveling at 10 cm/sec would run the 40-yard dash (3,657 cm) in 365 seconds or 6 minutes.
Another way of looking at this…
A person walks around 1.4 meters per second or 140 cm/sec.
In comparison, here are some other flammable gaases and their buring velocities…
|
Lower flammability limit (% vol.) |
Upper flammability limit (% vol.) |
Stoichiometric concentration (% vol.) |
Burning velocity (cm/sec) |
|
|
Hydrogen |
4.0 |
75 |
30.8 |
320 |
|
Acetylene |
2.5 |
(100)1 |
7.7 |
170 |
|
Ethylene |
2.7 |
36 |
6.6 |
69 |
|
Carbon monoxide |
12.5 |
74 |
29.8 |
43 |
|
Propane |
2.1 |
9.5 |
4.0 |
42 |
|
Butane |
1.8 |
8.4 |
3.1 |
42 |
|
Methane |
5.0 |
15 |
9.4 |
37 |
|
1 – Pure acetylene will undergo explosive decomposition. Data from Zabetakis, M. G. (1965). U.S. Bureau of Mines Bulletin 627. |
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