Discussion
of
"
Off­
Nominal"
Operating
Conditions
for
Catalyzed
Small
Off­
Road
SI
Engines
and
Lawn/
Garden
Equipment
Dr.
Ranajit
(
Ron)
Sahu
Consultant
to
OPEI
Oct
26th,
2005
Off­
Nominal
Conditions
°
Unintentional
and
unavoidable
conditions
during
equipment
operation
°
Occur
with
non­
trivial
frequency
°
Often
low­
frequency,
high­
consequence
events
°
Can
lead
to
significant
increase
in
fire
and
heatrelated
safety
hazards
Potential
Heat­
Related
Hazards
With
Catalysts
°
Temperatures
can
reach
over
1400
º
F
°
Ignition
of
the
turf­
work
surface
°
Accumulation
and
ignition
of
debris
close
to
hot
surfaces
°
Ignition
of
fuel
vapor
during
refueling
°
Ignition
of
fuel
vapor
due
to
leakage
from
fuel
system
components
°
Risk
of
burns
to
the
operator
or
bystanders
°
External
fires
caused
by
any
of
the
above
Four
Categories
of
Off­
Nominal
Conditions
°
Increase
in
amount
of
air
present
in
muffler/
catalyst
region
°
Air/
Fuel
ratio
changes
affecting
catalyst
conversion
efficiency
°
Increase
of
unburned
fuel
into
muffler/
catalyst
or
on
hot
surfaces
of
the
equipment
°
Changes
in
the
cooling
air
flow
management
system
Excess
Air
Into
Muffler/
Cat
°
Development
of
air
leakage
pathways
 
Holes,
cracks
 
Deviations
from
designed
secondary
air
injection
 
Deterioration
due
to
use
°
Modification
of
exhaust
exit
condition
can
result
in
air
intake
through
the
discharge
opening(
s)
A/
F
Ratio
Changes
°
Operation
of
the
engine
with
the
choke
on
°
Fuel
leakage
past
the
carburetor
float
°
Air/
fuel
changes
in
the
carburetor
°
Conditions
where
the
equipment
runs
with
either
a
clogged
or
missing
air
filter
Unburned
Fuel
Impacts
°
Misfiring
of
a
single
cylinder
engine
°
Failure
of
one
cylinder
to
fire
in
a
two­
cylinder
engine
°
"
Long"
engine
coast­
down
times
after
ignition
shut
off
°
Inadvertent
fuel
spillage
by
the
operator
causing
flammable
fuel
vapor
°
Tipping
to
access
the
underside
of
equipment
Changes
in
Cooling
Air
Flow
°
Debris
accumulation
in
the
cooling
air
intake
of
the
engine
or
equipment
°
Debris
accumulation
in
the
air
flow
passages
°
Debris
accumulation
between
the
exhaust
system
and
the
intended
cooling
air
source
°
Loss
of
gaskets,
seals,
baffles,
etc.
associated
with
air
flow
management
Simulation
of
Off­
Nominal
Conditions
°
Can
generally
be
simulated
via
laboratory
procedures
to
assess
the
thermal
and
fire
impact
of
conditions.

°
OPEI
members
are
ready
to
discuss
and
assist
in
the
development
of
detailed
procedures
to
simulate
"
off­
nominal"
conditions.
Next
Steps
°
Development
of
consensus
based
test
protocols
to
simulate
off­
nominal
concerns
through
broad
stakeholder
involvement
in
a
transparent
process
 
EPA
 
ICFSHE
/
SP
Fire
Technology
 
OPEI
 
Others
°
Establish
next
meeting
date
with
stakeholders
