Environmental Engineering Reference
In-Depth Information
diffuses into the ambient air to concentrations below the 5% LEL. In order to pose an explosion
hazard, methane must migrate from the landfill and be present between its LEL and UEL.
Other landfill gas constituents (e.g., ammonia, hydrogen sulfide, and NMOC) are
flammable. However, because they are unlikely to be present at concentrations above their
LELs, they rarely pose explosion hazards as individual gases. For example, benzene (an
NMOC that may be found in landfill gas) is explosive between its LEL of 1.2% and UEL of
7.8%. However, benzene concentrations in landfill gas are very unlikely to reach these levels.
If benzene were detected in landfill gas at a concentration of 2 ppb (or 0.0000002% of the air
by volume), then benzene would have to collect in a closed space at a concentration 6 million
times greater than the concentration found in the landfill gas to cause an explosion hazard.
Table 6 provides a summary of the potential explosion hazards posed by the important
constituents of landfill gas. Methane is the most likely landfill gas constituent to pose an
explosion hazard. Other flammable landfill gas constituents are unlikely to be present at
concentrations high enough to pose an explosion hazard. However, the flammable NMOC do
contribute to total explosive hazard when combined with methane in a confined space.
2. LFG asphyxiation hazard
Landfill gas poses an asphyxiation hazard only if it collects in an enclosed space (e.g., a
basement or utility corridor) at concentrations high enough to displace existing air and create
an oxygen-deficient environment. The Occupational Safety and Health Administration
(OSHA) defines an oxygen-deficient environment as one that has less than 19.5% oxygen by
volume. Ambient air contains approximately 21% oxygen by volume. Health effects
associated with oxygen deficient environments are described in Table 7. Any of the gases that
make up landfill gas can, either individually or in combination, create an asphyxiation hazard
if they are present at levels sufficient to create an oxygen-deficient environment.
Table 7. Health Effects from Oxygen-Deficient Environments
Oxygen Concentration
Health Effects
21%
Normal ambient air oxygen concentration
Deteriorated night vision (not noticeable until a
normal oxygen concentration is restored), increased
breathing volume, and accelerated heartbeat
17%
Increased breathing volume, accelerated heartbeat,
very poor muscular coordination, rapid fatigue, and
intermittent respiration
14 to 16%
Nausea, vomiting, inability to perform, and
unconsciousness
6 to 10%
Spasmatic breathing, convulsive movements, and
death in minutes
Less than 6%
Source: Cheremisinoff 2003
Carbon dioxide, which comprises 40% to 60% of landfill gas, may pose specific
asphyxiation hazard concerns. Because it is denser than air, carbon dioxide that has escaped
from a landfill and collected in a confined space, such as a basement or an underground utility
corridor, may remain in the area for hours or days after the area has been opened to the air
