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Buildings
Main Issues
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Damage to buildings and building systems from volcanic ash
can range from complete or partial roof collapse to less catastrophic
damage of exterior materials and interior rooms, including appliances
and computers, floor coverings, and electrical and mechanical
systems. These effects depend on several factors, including
the thickness of ash, whether it is wet or dry, the roof and
building design, air-handling systems, and how much ash gets
inside a building. Damage to the interior of a building can
be significantly reduced by taking several key steps before
an ash fall begins. For example, shutting down a building's
mechanical systems and air conditioners, protecting air intakes,
and closing other openings (doors and windows). |
After an ash fall, removing ash from the roofs
of buildings is usually a top priority in order to (1) prevent
roof collapse; (2) reactivate the ventilating and air-handling
systems; and (3) coordinate community-wide clean-up effortsclean
from roof to ground (roofs need to be cleared first so that
ground-level areas are not covered again by windblown ash from
roofs above). Rapid cleanup and restoring normal operation of
public buildings can significantly improve public morale and
confidence after an ash fall.
Caution: Be extremely careful when working to remove ash
from roofs and gutters and when sealing a home or building
before an ash fallinjury or death can result from falling
from a roof or ladder.
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Ash loading on roofs
A primary concern during ash fall is the potential collapse of buildings
from the accumulation of ash on roofs, which can lead to widespread injuries
and deaths. For example, the collapse of roofs from falling ash during the
explosive eruption of Mount Pinatubo on June 15, 1991, killed about 300. Historical examples of the effects of ash accumulating on
roofs are provided below.
If ash fall is expected, a survey should be made of the strength of roofs
in the area and of the maximum thickness of ash that they will bear without
danger of collapse, especially for critical facilities and buildings which
are expected to provide refuge for people during ash fall. Such surveys must
take into account the density of both dry and wet ash.
The effects of volcanic ash on roofs depend primarily on:
Ash density and thickness
The specific weight of dry ash can vary from 400 to 700 kg/m3,
and rainwater can increase this by 50-100 percent or more if the ash becomes
saturated by rain, sometimes reaching more than 2,000 kg/m3. The
problems of loading by ash are similar to those from loading by snow, but
the effects of ash accumulation are much more severethe load due to ash
is typically much greater (see table below), ash doesn't melt, and the ash
can clog gutters and cause them to collapse, especially after rainfall.
In areas that have snow-loading codes, some protection against ash may result
but his is highly dependent on the location of structures because snow load
levels vary with altitude and location.
Density & load comparison, 10 cm of snow and 10 cm volcanic
ash
(Johnston, 1997; p. 75)
New snow |
50-70 |
0.05-0.07 |
Damp new snow |
100-200 |
0.1-0.2 |
Settled snow |
200-300 |
0.2-0.3 |
Dry uncompacted ash |
500-1,300 |
0.5-1.3 |
Wet compacted ash |
1,000-2,000 |
1.0-2.0 |
The load on a bulding is given by the equation:
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Loading of volcanic ash on a roof for wet ash and dry ash. The
ash is assumed in this example to have a dry (compacted) density
of 1,000 kg/m3 and a saturation of 50% water by volume
and therefore a wet density of 1,500 kg/m3.
From Johnston, 1997; p. 74
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The effects of ash loads on buildings vary greatly depending of their design
and construction, including roof slope, construction materials, roof span
and support system, and age and maintenance of the building. In general, flat
roofs are more susceptible to damage and collapse than steeply pitched roofs,
and roofs made of smooth materials like sheet metal and glass are more likely
shed volcanic ash than roofs made of rough materials like thatch and asphalt
or wood shingles.
Buildings designed to withstand a heavy load of winter snow will clearly
support thicker accumulations of ash than buildings not engineered for any
type of load or shear stress. Surveys of buildings damaged from the accumulation
of ash during the eruptions of Mount Pinatubo in the Philippines and Rabaul
Caldera in Papua New Guinea indicate that roofs with wide spans (for example,
warehouses) are more vulnerable to collapse than buildings with short spans
typical of small homes.
Contrasting effects of ash loading on buildings, 1991 eruption of
Mount Pinatubo, Philippines
Collapsed building with long
roof span
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Nearby home with short roof
span
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Ashfall from the 15 June 1991 eruption
of Mount Pinatubo resulted in the accumulation of 5-10 cm of
wet ash in the area of former U.S. Clark Air Base, located 20 km northeast
of the volcano. Densities of ash samples collected here ranged from
1,200 to 1,600 kg/m3 (dry) and 1,500 to 2,000 kg/m3
(wet).
A survey of damaged buildings in Castillejos, 27 km southwest of
Mount Pinatubo identified the roof structure as the most significant
indicator of damage in a comparison of residential and nonresidential
buildings. Sixteen percent of surveyed buildings with short-span
roofs suffered major damage, with 43 percent having no significant
damage. Seventy-five percent of buildings with long-span roofs (greater
than 5 m clear span) were severely damaged, and only 17 percent
were without significant damage (Spence and others, 1996, p. 1059).
See online report, Building damage caused
by the Mount Pinatubo Eruption of June 15, 1991.
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Complex roof profiles or geometry and obstructions on roofs such as chimneys,
parapets, roof tanks or solar panels may lead to a greater accumulation of
ash next to these features if the ash is drifting with the wind. Such uneven
accumulation of ash on roofs can lead to an unbalanced load on the roof, increasing
the potential of roof failure (Blong, 1984, p. 206-208). Also, ash loads against
these obstructions may lead to their failure and, indirectly, to failure of
the roof.
Historical eruptions: effects of ash loads on buildings
1994 Eruption of Rabaul, Papua New Guinea
The effects of various ash loads on buildings in
Rabaul, 1994
Ash thickness1 in mm
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Estimated load2 in kPa
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Observed damage to roofs |
<100 |
1.5 - 2.0 |
Roofs and guttering generally remained
intact. |
<200 |
3.0 - 4.0 |
80-90% of roofs remained intact with
little apparent damage. Sagging or partial collapse occurred in
some buildings. |
<300 |
4.5 - 6.0 |
More than 50% of roofs did not
collapse. |
500-600 |
7.5 - 12.0 |
More than 50% of roofs collapsed. |
>600 |
9.0 - 12.0 |
It is doubtful that buildings survived
without significant damage even when the roof remained relatively
intact. |
1Ash
fell wet
2Using this equation and assuming
ash density of 1,500 to 2,000 kg/m3
Data from Blong and McKee, 1995. |
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Mount Pinatubo, Philippines, 1991 (Spence
and others, 1996)
A
survey was conducted of 51 buildings damaged in Castillejos, a town with a
population of less than 50,000 located 27 km southwest of Mount Pinatubo.
The thickness of ash in the town was about 20 cm. For the survey, the building
analysis included identification of (1) principal constructional materials
used; (2) number of stories; (3) roof structure, shape, and pitch; and (4)
building's usage (residential or nonresidential). The principle cause of damage
to the sample of buildings was that the load of ash on the roof exceeded the
strength either of the roof sheets or of the roof supporting structure, or
both. The load of 15-20 cm of water-saturated ash on roofs would have exerted
a force of 3kN/m2.
In a summary of the damage, the authors identified the following:
- Although many roofs had been cleared by the time of the survey, there
was evidence from the uncollapsed roofs that the wet ash was able to accumulate
to depths of at least 15 cm on metal sheet roofs of pitch up to 25 degrees,
without slipping from the roof.
- Out of the total sample of 51 buildings in Castillejos, 17 suffered partial
or complete roof damage, while 18 suffered no damage or only light damage.
- Buildings tended to suffer worse damage if they were (a) constructed with
long-span roofs (greater than 5 m clear span), rather than with short-span
domestic scale construction; (b) of timber frame rather than reinforced
concrete frame construction; (c) of higher rather than lower roof pitch;
or (d) non-residential rather than residential.
- Some other factors that seem to have contributed to damage, though statistical
evidence is inadequate to demonstrate their significance are (a) unbraced
supporting walls or columns; and (b) large unsupported roof overhangs.
According to the authors "to protect lives, roofs of buildings exposed
to possible ash fall should be designed for a superimposed load related to
the probable level of ash fall, in a manner analogous to design for now loading
in cold climates."
Ash corrosion on roofs and exterior materials
Ash can cause corrosion and may be electrically conductive. To minimize effects,
tape plastics (garbage bags, plastic wrap) over external building electronics
and metal surfaces, for example, security system displays, swipe card door
locks, alarms, and electrical panels.
Metallic roof surfaces, particularly older galvanized roofs which are pitted,
and lower gauge galvanized roofs are most susceptible to increased deterioration
from the properties of ash. To prevent or reduce the accelerated deterioration
of roof coatings by mildly acidic property of ash, clean and/or protect the
roof surfaces accordingly.
Ash may clog & collapse gutters and drains
Because gutters and drains are designed to collect water from roofs,
they are perfect "ash traps" and one of the most susceptible parts
of a building to damage from ash fall. A gutter that fills with ash, especially
if the ash is wet, can easily pull apart or collapse from a roof.
The many downspouts and drains attached to gutters may also become clogged
with ash, especially when it rains or if water is used to remove ash from
a roof. If the drain pipes deliver water to a dry well, the ash can seal the
well, making it inoperative.
For these reasons, it is important to keep roof drains and gutters clear
of ash as much as possible.
If a building's down-spouts and drains are designed to deliver water to a
community's wastewater delivery system and water-treatment facilities, effort
should be made to disconnect or block a building's roof drains before or immediately
after an ash fall to prevent ash from entering the drains and waste-water
systems.
Removing ash from roofs
The most obvious action to take for ensuring the safety of a building is
the removal of ash from the roof. Before beginning a cleanup operation, it
may be advisable to check insurance policies to see if any actions undertaken,
or inaction in some circumstances, may void the policy with respect to damage
due to the ash or cleanup process.
When should ash be removed from roofs?
The range of ash densities, roof design, and construction techniques make
it difficult to determine when during an ash fall that ash should be removed
from a particular building's roof. Clearing ash from a roof may prevent
collapse but such a decision must be weighed against the risk of personal
injury working in a dark, ash-rich environmentpeople easily slip
from roofs, fall from ladders, and fall through weak roofs while clearing
and removing ash. Also, if an ash fall is accompanied by rain, the roof
may become slippery and the wet ash could be difficult if not impossible
to shovel or sweep.
It may be advisable to remove ash before it exceeds a thickness of
10-15 cm, but only if the roof is easily accessible and the ash
can be removed safely. Because it is often dark or "pitch black"
during an ash fall, it may not be possible to safely remove ash until
a later time. After an ash fall, buildings which have received more
than 10-30 cm of ash and that have not collapsed still run a high risk
of load damage (for example, with the addition of more weight during
cleanup operations). The ash should be removed, however, as soon as
it can be done safely.
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Things to consider before removing ash from roofs:
- Know what plans your community has developed for disposing ash that
you collect.
- Coordinate your clean up efforts with those of your neighbors and
community to prevent the need for more than one ash-removal project,
especially from public streets.
- Communities(1) promply notify building owners to remove ash
from roofs in a timely manner (or according to a specific schedule)
to prevent streets from having to be cleaned many times; and (2) inform
the public of effective methods for removing ash from roofs and property
and preparing it for pick up by clean-up crews and organizing neighborhood
cleanup activities (see Cleaning up volcanic
ash).
- Prevent ash from entering the waste-water delivery system (or sewers)
by (1) disconnecting drains and downspouts from roofs; and (2) not
placing ash where it can be swept by water into the waste-water system
UNLESS told to do so by your community and neighborhood cleanup plans.
- Remove ash before the first rain if possible; to reduce the amount
of billowing during clean up, first dampen the ash with a light spray
of water (do not use large amounts of water because the ash may form
a glue-like "cake" material, which is difficult to remove
and adds considerable weight to the roof).
- Do not flush ash into drains and downspouts, because ash may clog
them. Ash flushed into dry wells can seal them, rendering them inoperable.
- Small vacuum equipment is usually not very practical for removing
ash from roofs because of the abrasiveness of ash and the enormous
volumes of ash that typically needs to be removed.
- Take action to prevent ash from entering the building during ash
removal (for example, plastic coverings over windows and doors).
- Ash shovelled or pushed off a roof may accumulate at the sides of
a building and exert pressure against the walls; it may be necessary
to remove this material at the same time the roof is cleared of ash
in order to reduce or eliminate the pressure.
Safety steps to take into account when removing ash from a roof:
- Be extremely careful when working on a roof, especially roofs with
even a low to moderate pitch and slippery material.
- Use personal protective measures when removing ash from roofs; for
example, using a strong ladder, safety harness, filter face mask,
gloves, and eye goggles.
- Prevent unnecessary damage to roof material and surfaces by using
protective measures during cleanup; for example, use planking, mats,
plywood sheets, and pliable footwear to prevent damage from impact
and abrasion; when using shovels, rakes, or other tools, be careful
of the underlying roof surface; the full force of water from fire
hoses can easily break lap shingles or tear lap roofing material.
Recommendations for removing ash from roofs:
- Remove all traces of ash near intakes of ventilation systems.
- Cover and seal intakes of ventilation systems around the building.
- Prevent ash from entering building through windows and doorways
seal doors and windows and control access into buildings.
- On flat roofs, hand sweep the ash into rows and transport
it by wheelbarrow to the edge of the roof; use planking, mats, plywood
sheets, and pliable footwear to prevent damage from impact and abrasion;
hoppers with a funnel pipe suspended above a loading truck may be
helpful; to remove the final residue or thin layer of ash, an air
compressor may be useful but only if the pressure can be regulated.
- On steep shingle roofs, place dams in the troughs to prevent
ash from reaching the drains and downspouts, then hose down the ash
and clear it from the eave troughs and gutters. This operation must
be performed with care to avoid deforming the gutters and tearing
them loose.
- On low-slope bitumastic mopped roofs, where there is only a thin
ash layer or small residue, flush the ash with water; use extreme
caution from high-pressure water hoses, which can easily damage such
roofing materials.
Modified from, FEMA, 1984
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The abrasive and mildly corrosive nature of ash can damage mechanical and
electrical systems. Air-handling systems and air conditioners are vulnerable
to ash damage and air-filter blockage, especially if air intakes are horizontal
surfaces. Damage can be prevented by turning off such systems before an ash
fall begins or immediately at first signs of ash fall. In many cases damage
can be avoided by taking steps to avoid use and contamination during ashy
conditions and thorough cleaning of equipment.
In buildings where air quality is critical, for examples hospitals, any action
should be taken under the advice of qualified personnel and engineers.
Recommended steps for air-handling systems (FEMA,
1984):
- Shut down air-handling and air-conditioning systems prior to or duing
the initial onslaught of ash fall.
- Close and seal air intakes; use internal circulation only to create
positive pressure inside building.
- Close and seal windows, doors, and other openings of buildings.
- Before re-starting air-handling system, clean and remove ash from
near external air intakes and roof area adjacent to the intakes; clean
or replace filters; inspect, clean or lubricate moving portions of the
system following prescribed routine maintenance procedures.
- Restrict vehicle and foot traffic near air intakes.
- Consider installing intake hoods that extend higher above the ground.
- Install pre-filters.
To restart air-handling systems:
- Clean the air intakes and the roof area adjacent to the intakes.
- Clean or replace filters.
- Inspect, clean or lubricate moving portions of the system following
prescribed routine maintenance.
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The abrasive and mildly corrosive nature of ash can damage computer and electronic
systems. When possible, the best damage-preventive strategy is to shut down
all computer, electric motors, and electronic systems until the ash has been
completely removed from the equipment and the surrounding area, including air-supply
and ventilation systems. Electrical panels can short out because of the high
level of electical conductivity of wet ash. For electronical systems and components,
the goals are to keep ash out of electronics, controlling what gets in, and
cleaning and disposing of the ash.
Electric motors
Ash can increase the wear on brushings, brushes, thrust bearings and commutators
on electric pump motors and other drive motors. Small motors blanketed with
ash can generate heat and could become fire hazards (FEMA, 1984).
Recommendations for cleaning motors (FEMA, 1984):
- Turn off electric motors and machinery before cleaning them. Throw
the motor switch as well as the main circuit breakers.
- Clean the electrical equipment using air pressure of 30 psi or less
to avoid getting a sandblast effect on delicate parts. Vacuum, where
possible, and change filter bags often. Avoid damaging surfaces by rubbing
or brushing them. Do not blow ash into places that should be kept clean,
and always follow manufacturer's recommendations for cleaning equipment
operated under dusty conditions. Increase maintenance servicing as recommended.
- Watch for electric shocks when operating ashy and dusty equipment.
Be alert to the possibility of overheating and fires.
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Computer systems
Computer heads and discs, and any high-voltage circuits, are especially vulnerable
to ash upset and damage. Ash on digital circuits will not cause much of a
problem becasue of the low voltages involved. High-voltage or high-impedance
circuits are very vulnerable to leakage caused by semiconductive ash. Ash
that is acidic is conductive as well as corrosive. Continual cleaning and
aggressive protection of computer systems should allow for continued operation
in all but the heaviest ash fallout (Labadie, J.R., 1994).
Techniques for cleaning include (from Labadie, J.R.,
1994):
- Clean and condition surrounding air to keep ash out of equipment.
- Cotton mat filters used in separate clean rooms were found to be best
for filtering particles, but they reduce the air flow. A solution is
to use larger fans to maintain required air flow. Rack-mounted equipment
can be modified to add a larger fan, but smaller instruments or components
with a built-in fan would require design change to increase fan capacity.
Use fluted filters as a compromise; increases surface area but reduces
air flow by only about 20%.
- Digital integrated circuits can vary 5-10% in performance (depending
on type of circuit) and still be acceptable. It is difficult to generalize
about other equipment (e.g. high-voltage power supplies).
- Humidifying ambient air (for example, wetting carpets) will help to
control ash reentrainment.
- Ash on equipment can be blown out with compressed air. If the air
is too dry, static discharge could damage sensitive components (for
example, integrated circuits). If the air is too damp, the ash will
stick. Relative humidity of 25-30% is best for compressed air.
- Cleaning with a pressurized water-detergent mix and a hot water rinse
is quite effective. However, this process requires at least partial
disassembly.
- Ash should be blown or brushed away from power supplies.
- Ash may have high static charge and be hard to dislodge, thus equiring
brushing to dislodge particles.
- Accelerate filter change; use pre-filters.
- Change to absolute filters; these will keep out particles down to
1 micron and smaller.
- Keep computer power on to operate filtration, but don't run (especially
disk drives).
- Maintain "room-within-a-room" configuration; restrict access;
re-circulate air; accelerate cleaning of the critical area.
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Appliances
- To reduce ash infiltration and reduce the need for extensive maintenance
of equipment, appliances, and machines, place coverings over the items as
standard procedure.
- Carefully monitor vacuum cleaners to assure that filters and ash bags are
changed when necessary.
- For appliances with electric motors, see electric motors.
Inside buildings and households
In general surfaces should be vacuumed to remove as much ash as possible
from carpets, furniture, office equipment, appliances, and other items. Portable
vacuum systems equipped with high-efficiency particulate filtering systems
are recommended whenever possible. The severity of ash intrusion depends on
the integrity of windows and entrances, the air intake features, and the care
exercised to control the transport of ash into a building or home via shoes
and clothing (see recommendations for keeping ash out).
Care should also be taken to avoid further contamination during the emptying,
cleaning, and maintenance of vacuum equipment.
Suggested ash removal from buildings and households
(FEMA, 1980):
- Cleaning by blowing with compressed air or dry sweeping should be
minimized.
- A dustless method of cleaning such as washington with water and an
effective detergent/wetting agent is recommended. Damp rag techniques
should be used whenever possible to remove the substance from small
surface areas or flooring. On those areas where damp rag techniques
cannot be implemented (for example, carpets) vacuum cleaning methods
should be applied.
- After vacuuming carpets and upholstery may be cleaned with a detergent
shampoo. Avoid excess rubbing action because the sharp ash particles
may cut textile fibers.
- Glass, porcelain enamel and acrylic surfaces may be scratched if
wiped too vigorously. Use a detergent soaked cloth or sponge and dab
rather than wipe.
- High-shine wood finishes will be dulled by the fine grit. Vacuum
surfaces and then blot with a cloth treated to pick up ash. A tack cloth
used by furniture refinishers should work well.
- Floor sweepers with side brushes should not be used to clear aisles
and floors beacuse they may re-entrain dust particles into the air.
- Ash-coated fabrics should be rinsed under running water and then
washed carefully.
- Soiled clothing will require extra detergent. Wash small loads of
clothing, using plenty of water so the clothes will have room to move
freely in the water. Do not mix heavily soiled clothes with garments
that are lightly soiled.
- Be sure clothes are free of ash before putting them in an automatic
dryer Ash may scratch the inner surface of the dryer.
- For several months after an ash fall, filters may need replacing
often. Air conditioner and furnace filters need careful attention. Clean
refrigerator air intakes. Clean any surface that may blow air and recirculate
the ash. Stove fans and vents should be cleaned thoroughly.
- Each employee should be responsible for clean-up of his/her own work
area to minimize exposure potential during a work shift. This should
be accomplsihed at the beginning of each workshift. Damp rag or vacuum
techniques should be used during this operation.
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Ash Disposal
Ash removed from inside buildings and homes should be disposed in accordance
to community plans and directions (for example, preparing it for pick up by
clean-up crews as part of neighborhood cleanup activities). It may be advisable
to request that people separate volcanic ash from normal garbage for collection
or disposal at a designated locationmixing ash with normal garbage can
result in damage to collection vehicles and take up space in landfills. Small
amounts of ash from vacuum cleaners have been disposed successively in household
gardens and lawns.
See full discussion of ash disposal issues.
During and after ash fall, keeping ash out of buildings and homes will significantly
reduce cleanup costs and prevent damage to surfaces, electronics, appliances,
floors, and other equipment.
- Restrict access to a building or home to the most protected entrance to
reduce the potential for ash to get inside.
- Establish an entry room or cleaning and decontamination rooms for people
entering the building. Provide vacuum cleaners and brushes for people to remove
as much ash as possible from clothing; provide shoe covers and disposable
caps as appropriate. Remove outdoor clothing before entering a building as
appropriate.
- Seal entrances and openings (doors, windows, dampers, air intakes). Place
damp towels at door thresholds and other draft sources; tape drafty windows.
- Establish any necessary, extra cleaning procedures to protect the interior
environment.
- Stockpile cleaning supplies, duct tape, disposal containers, vacuum cleaner
bags and filters.
- Use extra (and heavier) filters for external air intakes.
References
Blong, R.J., 1984, Volcanic hazards: a sourcebook on the effects of
eruptions: Academic Press, Australia, 424 p.
Blong, R., and McKee, C., 1995, The Rabaul eruption 1994: destruction
of a town: Natural Hazards Research Centre, Macqauarie University, Australia, 52 p.
Labadie, J.R., 1994, Mitigation of volcanic ash effects on aircraft operating
and support systems, in Casadevall, T.J., ed., 1994, Volcanic ash and aviation
safety: Proceedings of the first international symposium on volcanic ash and
aviation safety, Seattle, Washington, July, 1991: U.S. Geological Survey Bulletin
2047, p. 125-128.
Federal Emergency Management Agency (FEMA), Region X, 1984, The mitigation
of ashfall damage to public facilities: lessons learned from the 1980 eruption
of Mount St. Helens, Washington: [Seattle, Wash.], FEMA, 70 p.