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COMBUSTION
SAFETY CHECKS
How Not to Kill Your Clients
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People
who manage or work within programs that provide any
significant service inside a building need to be
familiar with the basics of combustion and
combustion safety. by Rob deKieffer
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Heating
contractors, inspectors, and energy auditors all have
different approaches to inspecting combustion appliances.
Combustion problems come in various sizes and shapes, and
individual tests may not by themselves prove if the house is
actually safe. Those of us who work in buildings must be able
to understand the signs, and know what and when to test, in
order to ensure that a small oversight does not result in a
long-term health problem for our client.
Knowing
some simple facts about combustion will make analysis easier.
Most common fuels have carbon (C) and hydrogen (H) locked up
and ready to heat. Add a consistent ignition source and some
oxygen and we have combustion. Breaking apart the
carbon-hydrogen bond produces heat and releases carbon and
hydrogen to find a new bond. On a good day, this will produce
water (H20), carbon dioxide (CO2) and a
bunch of hot air. This means that the carbon had to find some
oxygen. To do this, the combustion products must stay hot, and
oxygen has to be available. If there is insufficient oxygen,
the carbon has no choice but to remain carbon or become carbon
monoxide (CO).
Sometimes
the rules just do not make sense. For instance, houses with
gas ranges dump all of their combustion products directly into
the kitchen, so why all of the concern about these other
appliances? In Colorado, an average of more than six people a
year are killed and 50 people accidently poisoned by carbon
monoxide produced from furnaces, gas appliances, and kerosene
heaters. These numbers represent only the cases that are
properly diagnosed and reported to the state.
The
problems with combustion appliances are not simply with the
devices themselves, but how they work within the building. The
safety of the units depends on their installation, operation,
and maintenance. Other concerns such as competing air sources,
house tightness, and effects of remodeling all can be
important to the overall operation of the system.
In
developing a program that will check for the safety of
combustion appliances, three questions need to be answered:
What are you
trying to keep them safe from?
What is the
appropriate level of testing?
Once
these seemingly simple questions are answered and the goals of
the safety program are defined, standards and procedures can
be established to ensure the program will provide the desired
level of protection.
Saving
Your Staff
The
first and most immediate concern should be the safety of the
staff going into buildings and conducting tests. A good safety
check involves gathering information from the client, visually
inspecting the building, and running specific physical tests.
Of these, the visual identification of potential safety
problems is the most important.
The
immediate problems can be defined as those that pose imminent
danger. Two groups of concerns are air quality and fire
hazard.
Table
1.
Combustion Safety Problems,
1,000 Units |
|
| Carbon Monoxide |
5.0%
|
| Gas Leaks |
8.3%
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| Spillage |
2.4%
|
| Cycle Gas on High
Limit |
13.5%
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| Disconnected Ducts |
9.1%
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| Open Return Air Duct |
22.4%
|
| Over the
past ten years of testing houses for combustion
safety problems, the tests, testing equipment, and
procedures have changed. At Sun Power we examined
the results from 1,000 tests in 1990. |
|
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Table
2.
Sun Power's Draft Standards
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|
|
Outdoor temperature
|
Draft
|
| >80deg.F |
>.005 in. W.C.* |
| <80 but >32 |
>.01 in. W.C. |
| < 32 |
>.02 in W.C. |
| *Water column |
|
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Combustion
Safety Tools
Carbon
Monoxide Detector: ($150- $800) Mechanical
testers use a glass tube that is sensitive to
various levels of CO. Each tube costs $2 and can be
used 2-3 times in one day. Getting accurate flue
samples is difficult with the tube system.
Mechanical systems provide a digital readout of the
CO levels and are relatively reliable. They need to
be calibrated once a year and have a replaceable CO
sensor.
Draft
Gauge: ($20-$80) A variety of gauges can be used
to measure static pressure in the vent. The range
should be between 0 and .1 in. water column (W.C.)
and be able to withstand short durations of exposure
to hot flue gas.
Manometer:
($15-$65) Manometers can be either water or
fluid filled. For measuring natural gas pressure,
they need to have a range between 0 and 7 in. W.C.
For measuring propane, the range is between 0 and 14
in. W.C. We have found the 14 in. water filled are
the easiest to use (you fill it with water at the
site).
Orifice
Drills: ($100-$150) The drills are used to
determine the size of the orifice. When matched with
the pressure information, this can determine the Btu
input.
Efficiency
Testing Equipment: ($450-$3,500) To measure
steady state efficiency (SSE) you need to know the
stack temperature, combustion air temperature, CO
level, and either oxygen or carbon dioxide levels.
Both analog and digital equipment is available that
will test for all of the components. The low cost
equipment requires a separate tool and test for each
measurement.
Gas
Leak Detector: ($200-$250) Specialized soap
solutions are available (they do not freeze if left
in the truck) to verify leaks. Most equipment is
electronic and is sensitive to a wide range of
combustible gases.
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Carbon
Monoxide
in Ambient Air
Carbon
monoxide detection systems have advanced significantly in
recent years. Digital equipment can be used to provide an
indication of elevated ambient levels of CO. Sensors should be
turned on and calibrated in a noncontaminated environment,
typically outside the building. When preparing to test all of
the combustion devices, an ambient reading should be taken and
be close to zero. If the initial readings are measurable--0-9
parts per million (ppm) depending on the meter--the source
needs to be identified. In no case should exposure exceed 35
ppm.
Gas
Leaks
Gas
leaks pose a potential immediate threat of fire or explosion.
Leaks can be detected by smell, gas leak detection, or fluid
and electronic gas leak detectors. A combination of techniques
can be used to identify, and ensure the repair of, any leaks
prior to additional testing.
Roll-out
Flames
unexpectedly coming out the front of the appliance
("roll-out") indicates serious combustion problems.
Visual indications of roll-out will be seen on the appliance
body, in the form of black or rusted areas in front of the
burners, burnt wires, and carbon deposits. In these cases, a
client may mention that they occasionally hear a
"boom" when the furnace turns on.
Spillage
We
don't want our staff breathing combustion products for
extended periods of time. Combustion products can enter into
the living area of the house through disconnected venting
systems or systems which are not venting properly. Vents
should be visually checked for integrity. All draft diverters
should be tested with smoke to ensure that all of the
combustion products are leaving through the vent. Testing the
draft of the appliance will assist in determining the adequacy
of the venting system, but spillage is an immediate hazard.
There
are additional factors that affect the testing for these
immediate hazards. Our intent is to evaluate the house for
combustion safety under conditions that are most conducive to
creating a problem. To do this we need to have the house set
up in that condition. This means turning on air handling
equipment that may move air to the outside (dryers, bath fans,
kitchen fans) and closing the doors and windows.
A
protocol must be established and followed. Basic combustion
tests should be performed on a consistent time schedule.
Observation of the appliance's cycle provides indications of
operational components. The observation time should be at
least five minutes after ignition. This allows the device time
to establish a draft and reflects how it will operate on a
consistent basis. The protocol also needs to address different
configurations of appliances. If a furnace and water heater
are connected to a common vent, both appliances should be
tested independently and together.
Client
Safety
The
second level of concern is for the short- and long-term safety
of your client. Visual inspection of the house and appliances
is extremely important in this analysis.
Carbon
Monoxide
Are
there any signs of carbon monoxide being created? Is there any
carbon in the burner area, flue or vent? How are the flames
burning? Are there any visible signs of a problem, such as
flames burning erratically, no flames visible on part of the
burner, weak flames, or white tips on the flames? Regardless
of the visual inspection, a test must be performed to verify
that there is no CO in the combustion gases. The sample should
be taken from each flue (exhaust port), before additional
dilution air is added to the gases. In a furnace with four
burners, at least four tests should be taken. In a water
heater there should be a test taken on both sides of the
internal baffle. On a stove, a test should be taken in the
oven vent and above each burner. Sealed combustion units can
and should be tested as well.
Our
field experience has shown that problems with most units that
create CO in excess of 25 ppm in the flue can be corrected.
Most field standards are higher than this (less than 100-200
ppm). One of the key components of this step is to determine
why CO is being created, since CO is a symptom of something
being wrong with the building or unit.
Draft
and Venting
The
draft of the appliance measures the power of the venting
system to exhaust. The measurement of the draft is coupled
with a visual inspection of the venting system to determine
the probability that all of the combustion gases are getting
out of the structure. If the draft is measured in cold
weather, it can provide an indication of the ability of the
appliance to exhaust in warmer weather (if the draft is weak
in cold weather, it will be weaker in hot weather). The
standard we use was developed from both technical analysis and
field testing.
Combustion
Air Source
The
source of the combustion air for the appliance must be
adequate and not come from a prohibited location. (Having a
combustion appliance draw air from, and be connected to, a
bedroom is not a good idea.) The first test for adequacy of
the combustion air has already been completed: no CO, no
spillage, and sufficient draft. This test is to identify
problems you might have if you change the building tightness.
Having an open or not sufficiently connected return air system
is a primary concern. Open returns provide a significant
depressurization source in the immediate vicinity of the unit.
Standards
range from simply ensuring that the appliances work under the
worst case conditions, to installing combustion air that meets
current building code.
 |
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| Figure 1. Schematic of a
combustion furnace. |
Figure 2. Air paths in a
combustion furnace. |
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Key
Terms
Flue:
Part of the combustion venting system below the
draft hood.
Vent:
Part of the combustion venting system above the
draft hood that carries diluted combustion products
to the outside.
Primary
air: Air mixed with fuel before combustion.
Secondary
air: Air introduced into the combustion chamber
after combustion has begun.
Combustion
air: Air that is used to provide oxygen for
combustion.
Roll-out:
Flames and combustion products that exhaust from the
appliance at the burner area.
Spillage:
Combustion products that spill out of a draft
diverter and do not exhaust through the vent.
Draft:
A measure of the potential of a system to exhaust.
Draft
diverter: A safety device installed on
atmospheric appliances to (1) allow draft to divert
into the building if the vent becomes blocked, and
(2) add dilution air for draft efficiency (sometimes
called a draft hood).
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Appliance
Safety
Most
appliances are equipped with safety devices to prohibit them
from overheating and from allowing fuel into the device if
there is no ignition source. You should check the limits if
you are doing anything that might affect the heat transfer.
This can include cleaning blowers, repairing ducts, insulating
boiler pipes, and so on. The gas supply to a forced air
furnace should be turned off before the plenum temperature
reaches 275deg.F. If this occurs during the normal operation
of the unit, it can be indicative of an overheating problem
and should be corrected. Checking the pilot safety and 100%
closure of the main burner valve can also be done as a
precautionary procedure.
Cracked
Heat Exchanger
Examining
appliances for a breach in the heat exchanger is potentially
significant, but of lesser importance than the previous tests.
Checking for cracks is done by examining the flames for
interference when the blower is operating and by direct
inspection of the heat exchanger.
Other
Potential Problems
There
are a number of other code and safety issues that programs can
address. These are primarily addressed due to a specific
program bias or documented regional safety problems. These
include inspecting and repairing gas lines due to galvanized
pipe, copper pipe or soldered flex lines, testing fuses,
replacing venting due to improper materials or insufficient
clearance, gas pressure, and other items that do not meet
current building code.
Program
Safety
Those
who work in programs that provide any significant service
inside a building should be knowledgeable of the unanticipated
consequences of their actions. Changing a furnace filter,
changing a client's use of the thermostat, fixing a bath fan,
or hanging a door, can all potentially effect the operation of
combustion devices.
Liability
The
long-term liability will sit with those agencies that ignore
the facts. The facts show that the air inside buildings is
connected to a myriad of systems. These systems use the air in
different ways. If you want to avoid liability problems with
building failure or combustion problems, you need to test the
building and the appliances. Testing must identify problems
that exist before any work is done. Tests must also be done on
completion of work to ensure that the systems that were in
place were not adversely affected.
Other
combustion issues have a potential impact on liability such as
unvented combustion appliances and kerosene heaters. At Sun
Power we will not work on the building unless we can eliminate
those types of combustion appliances.
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Federal
Safety Commission Pushes CO Detectors
Odorless
and colorless carbon monoxide gas (CO) is the number
one cause of death by poisoning in the United States
and accounts for more than one in five of all
unintentional deaths by poisoning. Media accounts
generally cite government data showing 5,000 CO
deaths annually. This number comes from the U.S.
Centers for Disease Control, which estimates there
were 56,133 deaths from CO poisoning in the United
States between 1979 and 1988. Of the total, 41,622
deaths--nearly 80%--resulted from suicide, fires, or
homicide. Some 2,964 CO deaths resulted from
"unidentifiable" causes while 11,547
deaths were classified as "unintentional."
According
to the U.S. Consumer Product Safety Commission (CPSC),
in 1989, the most recent year for which statistics
are available, there were about 220 deaths from CO
poisoning associated with gas-fired appliances,
about 30 CO deaths associated with solid-fueled
appliances (like charcoal grills), and about 45 CO
deaths associated with liquid-fueled heaters.
These
numbers probably underestimate the number of people
exposed to non-fatal CO levels, because symptoms of
poisoning--including headaches, nausea, fatigue,
dizziness--are sometimes mistaken for the flu and go
untreated.
Reflecting
a growing awareness of the dangers of poisoning, the
CPSC--which recommends that CO detectors meeting
Underwriters Laboratory (UL) standard 2034 be
installed in all existing residential buildings--has
been moving toward requiring the detectors in newly
built homes. The CPSC is also working with state and
local code jurisdictions to incorporate CO detector
requirements into state and local legislation, and
is working with the National Fire Protection
Association to develop a national installation
standard.
Detectors
meeting UL standard 2034 currently cost between $35
and $80. (for a list of manufacturers meeting the
standard, contact UL, 333 Pfingsten Road,
Northbrook, Illinois, 60062-2096, Tel:
[708]272-8800). Because the toxic effect of CO
depends on both concentrations and length of
exposure, long-term exposure to a low concentration
can produce effects similar to short-term exposure
to a high concentration. Detectors meeting the UL
standard, therefore, measure both high
concentrations over short periods, and low
concentrations over long periods. It is estimated
that between one and two million such detectors are
now in the marketplace, but demand for them is
expected to grow rapidly (especially if codes
require them).
Chicago's
Experience
Following
several deaths by CO poisoning, and one particular
case where an improperly installed furnace killed a
family of ten, Chicago last year became the first
city to adopt an ordinance requiring UL-approved CO
detectors in all new single-family homes and in
existing single-family residences equipped with new
combustion furnaces.
The
ordinance, however, has been somewhat controversial.
When a detector alarm sounds, residents open doors
and windows to ventilate their homes, and then call
the fire department, gas utility, poison control
center, or another response agency. When inspectors
appear at the home, they may not be able to detect
CO because the windows were opened. This leads to
questions about whether the alarm sounded at an
appropriate level, whether it was accurate, and so
on.
With
a burgeoning demand for CO detectors, proper
protocols and measurement methods for responding to
alarms are needed so that questions about the extent
to which alarms represent actual situations of
elevated CO levels can be answered. Who, for
example, should respond to an alarm and under what
conditions--the fire department, a heating
technician, or the local utility?
In
a space of two months, Chicago's fire department
last year responded to nearly 6,000 calls, but
according to one department spokesman, all but 33 of
them were "unfounded." The fire department
reportedly received 244 "unfounded" calls
on Thanksgiving day alone.
Some
city officials have called for a repeal of the
ordinance, but other officials credit the ordinance
with having saved 40 lives thus far.
Underwriters
Laboratories, meanwhile, is considering changes to
its CO detector standard. One proposal would change
the "stability test" from 15 ppm for eight
hours to 15 ppm for 30 days so that detectors would
ignore lower CO concentrations. The standard was
written in the context of the existing technology
for detectors (in 1992) and new technology may soon
dictate a need for an updated standard.
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Steps
to CO Production
The
most common carbon monoxide (CO) problems involve a
lack of oxygen - either because there is simply not
enough, or because the flames cool off before the
carbon can join with it. CO is produced whenever a
fuel is burned without enough oxygen on hand. Carbon
atoms in the fuel that normally join up with two
oxygen atoms to form carbon dioxide, which is
harmless to human health, end up with only one
oxygen atom and instead form CO.
Basic
Steps to Getting CO Into Your Life
It
is not enough to understand how to create CO, we
need to examine all of the coordinating factors
which can create it and allow it into the living
space.
Five
basic factors not only lead to the production of CO,
but will aid in getting it into your homes. Any one
major failure can get CO into your home, but
typically three of these factors must go awry to
produce a major problem.
The
Flow of Fuel
As
you add fuel to a fire, the fire produces more Btus
of heat. It also requires more oxygen to combine
with the carbon and hydrogen to form carbon dioxide
and water vapor (H2O. As you continue to add fuel,
the amount of available oxygen needs to keep up or
CO will be produced, which is incompletely burned
carbon. In engineered systems (all modern combustion
appliances) the amount of air that can move through
the unit is limited by the design. Any additional
restriction (dirt, lint, carbon) will result in the
air flow being reduced. The air flow is controlled
by the laws of nature (hot air rises). The flow of
fuel is controlled by the pressure applied to the
fuel and the size of the hole it is forced through.
Any problem with the pressure of fuel input can lead
to problems with the fuel/air mixture.
Competition
for Air
We
refer to many kinds of air when describing a
standard combustion appliance (combustion air,
primary air, secondary air, dilution air, return
air, supply air, and so on). Air, or more precisely
the oxygen in the air, is fundamental to the
combustion process. The amount of air than can come
into standard appliances is typically controlled by
two basic systems. First is the mix of gas and air
before combustion (primary air). This is controlled
by the design of the burner, the pressure of the
gas, and any control of the air stream. The
secondary air, or additional air that is needed to
supply oxygen to the flames, is simply controlled by
the amount of air that is drawn through the heat
exchanger.
In
order for these two simple systems at the appliance
to supply adequate oxygen for complete combustion,
there needs to be sufficient air to the area around
the appliance. Any competition for the air needed
for the combustion process can lead to problems. The
power of the competition does not need to be strong
to overcome the natural forces of the combustion
appliance.
Venting:
The Wild Card
Getting
all of the combustion products out of the living
space, a matter of indoor air quality, is
fundamental to the safety of our clients. Codes and
venting systems are designed to ensure this happens.
In the cases that combustion appliances are unvented
(they vent into the living space), there are
specific directions for additional ventilation needs
(like opening a window).
Venting
can be a wild card due to its relationship to both
the weather and the physical configuration, time of
year, time of day, connection with other appliances,
connection with the house, and so on. All of these
relationships can have a dramatic effect on the
draft of an appliance. The fundamental principle is
that hot air rises. We can thus figure out how much
area in the vent is needed to get all the combustion
products out of the building. These rules may not
always result in successful venting in actual
buildings. Only testing can provide an indication of
the operation.
Operation
The
operations of the appliance can be broken down into
two components: those defined primarily by the
internal controls of the unit and those dictated by
the occupant. We have found many units where the
appliance is not able to operate correctly and that
just happened to keep the unit from being a major
liability to health and safety. Changing any portion
of the operation may affect safety. This includes
adjusting the distribution, air tightness of the
unit, ductwork, load/insulation, not to mention
touching the unit itself. The client's operation of
the unit can also affect safety.
Luck
(Or Lack of)
Luck
is the final card. It is the random combination of
the first four factors and other things that affect
the building. Simple things like unclogging a dryer
vent, fixing a bath fan, repairing ducts, or
insulating walls, can change the operating patterns
of the combustion devices.
How
it Happens
In
addition to the five basic components, we have seen
significant patterns in the creation of CO.
Very
few HVAC installers have the equipment necessary to
ensure a safe installation of a combustion appliance
is completed. Many units create CO because of
improper setup and testing. Problems with gas
pressure, orifice size, and improper venting are the
most common.
Remodeling
Remodeling
a building often involves adding walls and changing
the combustion air location and source availability.
At Sun Power we have seen new house designs which
virtually ensure that the combustion air source will
be eliminated. In addition to limiting the
combustion air, remodeling typically increases the
pollution in the area of the combustion devices (for
instance installing a dryer in a small room with the
furnace).
Deterioration
and Proper Installation
Long-term
deterioration of an appliance is not a common factor
leading to CO production. However, deterioration is
a common problem with units that were marginally
installed: vents with long horizontal runs may have
just met standards when they were installed but are
prone to rust out over time. Venting into an unlined
chimney can lead to problems (erosion of the chimney
can eventually lead to leaks). Dirt from a
crawlspace can fall down and block the combustion
air hoes in a water heater. Even crawlspace furnaces
stay fairly trouble-free unless major contaminants
are introduced into the area. Dryers and water are
the chief causes, but rust and lint are good at
blocking everything.
CO
can be drastically reduced in the home if the units
are installed correctly in a dedicated area which is
not connected to the living space. This requires a
room for the combustion appliances that is vented
with outside combustion air (or sealed combustion
units) and has sealed ductwork.
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Setting
Your Standards
For
every program there needs to be a written set of standards.
These standards provide the basis for any work done and give
management a basis to evaluate the coverage and liability
exposure. An example of such a standard is: No furnace or
water heater may have over 100 ppm carbon monoxide in the
flue. This establishes the quality threshold which needs to be
maintained.
Written
policies and procedures must be in place to establish how
these standards are to be met--or, more importantly, what is
not wanted. As in the previous example, the policies will
establish how much money to spend to correct the problem, what
to do if the problem cannot be fixed, whom to contact, and so
forth. The procedures will provide the guidance on what to do
first.
A
quality assurance program will help staff follow the policies
and procedures in pursuit of the quality standard. Effective
communication and training rely on having a quality assurance
program which can change and have direct input into improving
the staff's abilities. In the case of CO production, we want
to make sure that we have found the true cause of the problem
and that we have corrected the CO problem as inexpensively as
possible. We do not necessarily need to inspect the unit to
determine if the problem was properly diagnosed. Systems
should be in place to determine if staff understand the
process and a training component should be available to
improve abilities.
Focused
evaluation makes sure that the program intended to be
delivered is really in place. Many programs adopt standards
that do not relate to their building stock, climate, or
staff's ability. A good evaluation will show the strengths and
weaknesses in the system.
Evaluation
also needs to be used to examine technical issues such as: do
we need to simulate a fireplace draft when testing the other
appliances? Should we test the ability of the house and
appliances to backdraft the fireplace? How do the results of
the testing vary if the furnace is hot?
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Sun
Power's Furnace Specifications
|
|
| For
a job to be considered complete, the following
specifications must be met. This is not meant to be
an exhaustive list.
Forced Air
Standing Pilot Furnace
|
|
| Gas
leaks: |
No leaks
smelled in the building or detected with gas leak
solution |
| Venting
problems: |
Entire
venting system connected and intact (not
deteriorated to the point that it is falling apart)
and continuous to the outside of the building |
Carbon
monoxide
indicators: |
No carbon
built up anywhere in the system
No flame problems (ghost flames, inconsistent
pattern, flames hitting heat exchanger)
No white flames |
| Flame
interference: |
No flame
interference when the blower comes on |
| Carbon
Monoxide: |
<100
ppm in the flue. All reasonable attempts should be
made to eliminate CO |
| Spillage: |
No
spillage from around the draft hood or burner area
using smoke test with a light |
Draft/outside
temperature: |
Measured
draft in the vent must be higher than:
-005 in. W.C. @ >80deg.F
-.01 in. W.C. @ 30deg. to 80deg.F
-.02 in. W.C. @ <30deg.F |
| High
limit switch: |
Installed
and operating at 275deg.F
The furnace is not shut down by the switch during
five minute test |
| Open
return air: |
No open
returns in furnace room, or in a location that could
interfere with the combustion air for any combustion
device |
| Water
Heater |
|
| Gas
leaks: |
No leaks
detected with gas leak solution |
| Venting
problems: |
Entire
venting system intact |
Carbon
monoxide
indicators: |
No
carbon, no flames, no white flames |
| Carbon
monoxide: |
<100
ppm in the flue |
| Spillage: |
No
spillage using smoke tests with light |
Draft/outside
temperature: |
Measured
draft in the vent must be higher than:
-.005 in. W.C. @ >80deg.F
-.01 in. W.C. @ 30deg. to 80deg.F
-.02 in. W.C. @ <30deg.F |
Rob
deKieffer is executive director of
Sun Power Incorporated
in Wheat Ridge, Colorado.
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