Sludge Watch ==> Toronto sewage sludge pellets - and the fire that consumed the plant

[Maureen Reilly]

This article from the Ontario Fire Messenger may be of interest to Toronto 
sludge watchers as Toronto rebuilt the pelletizer that burned
down before the City took it over from USFilter (now called "Veolia")


The fire risk associated with sewage sludge pellets also forms part of
the problem with
Toronto sludge that needs to be assessed in the current Environmental
Assessment of Toronto's sewage sludge (biosolids) program. Toronto
pellets didn't always get dry. Some tested at 13% moisture (Toronto 2002
records) and this may account for the cases of smoldering fires in
storage.

Fire hazards of pellets also needed to be a consideration in the Health
Study assessment of Toronto's biosolids and sludge pellets programs, but was 
ignored.
Thus all the low termperature sludge smoke from farmfields, Couse Ltd's 
burning sludge shed in Tillsonberg, and the other places like 1281 Old 
Thorold Stone Road in Thorold where fire officials attended...none of these 
smoke and fire consequences to health and the environment were considered.

The fact that the pellets have been failing to meet Fertilizer Act 
requrements was also ignored in the Public Health pellet review documents.

http://www.toronto.ca/health/hphe/bio_solids.htm

The final cause of the fire that has burned down the USFilter pelletizer
plant in Toronto was the subject of a report by the Fire Marshall's
investigators.

The fire that burned down the Toronto pelletizer a few years ago was 
apparently
caused by the following:

There is hollow copper tubing filled with a heated thermal oil.  This copper 
tubing has
a trough in it and the pellets roll down the hot copper trough in the pipe, 
while the heat from hot oil inside the copper pipe dries them.

At the Toronto plant the thermal oil was heated over its flash point.  A 
valve failure in the copper tubing containing the heater thermal oil cause 
hot oil (heated over its flash point) to spray over the electical equipment.

The plant caught fire and the fire put a sudden end to the retirement party 
being held for Toronto's Water and Wastewater Director at the time: Bob 
Pickett.

Indeed he was just giving his farewell speech at the podium when his beeper 
and cell went off - rapidly followed by almost every beeper in the room- 
alerting them all that the pelleting plant was in flames.

It is not clear what modifications have been made to prevent a recurrence of 
this problem.
The issue of 'self-heating' sewage pellets should be of interest to whoever 
it was 'bought' Toronto's sludge pellets earlier this year.

I understand that sales were suspended, since the label was wrong...and 
these fire risk pellets are now being stored.

to see the Fire Marshall's report (there is a repetition of pages):

http://mysite.verizon.net/res7xl4c/ABTP%202003%20Fire%20Marshall%20Report.pdf

I met with the Assisstant Fire Marshall of Ontario just three weeks before 
the Toronto sludge pellet plant burned down.  He ignored the Sludge Watch 
warnings.

......................................................................................

The article below was published by the Ontario Fire Marshall's Office in
the Publication:
Ontario Fire Service Messenger November/December 2002

................................



Sewage sludge pellets: fire and explosion risks

There are rabbit food pellets, pellets for guns, wood pellets for
burning in stoves, and there are even sewage sludge pellets! What will
they think of next?

Introduction
Sewage sludge is the nutrient-rich organic byproduct of the wastewater
treatment process. It contains most of the nutrients required for crop
growth, and organic matter, which can enrich soil, and may also be
called “biosolids”.
For some people, spreading biosolids on farmlands is considered to be
perfectly safe way of returning nutrients to the ground if appropriate
procedures are in place. Recycling this nutrient source is viewed to be
better than putting it in a landfill site or incinerating it.
Other people believe that cities are simply transferring urban pollution
to the countryside, and site concerns about the fumes, respiratory
infections and other negative health effects that may stem from exposure
to biosolids, and the potential for contaminated well water and water
courses.
Sewage sludge can exist in liquid forms and can also be converted into
granules or pellets by removing the moisture. In this solid form,
pellets are easier to handle and store, and transportation costs are
reduced, as compared to liquid sludge.
Although people may be aware of the environment aspects associated with
the disposal of sewage sludge, they may not be aware that sewage sludge
pellets have been associated with numerous fires and explosions. For
instance,

* Sludge pellets stockpiled at a farm in Windsor caused a smoldering
fire.

* There were a series of explosions in a Windsor pelletization plant,
most recently in October 2002.

* The City of Toronto had problems with the self-heating of sewage
pellets in a storage silo.

* An explosion at the Miloganite plant in Milwaukee in 1996 caused
serious injuries to a worker and $ 4.5 million worth of damage to the
plant and property.

This article has been prepared to provide information on potential fire
hazards associated with sludge pellets, safe storage and effective fire
suppression.

Self-heating properties of the product:

Sewage sludge is mainly derived from human waste, but may also contain
animal products, paper, high fat content from processing plants, heavy
metals, organic contaminants and petroleum products from petroleum and
diesel spills. When formed into pellets, the finished product has less
than 5% moisture content.
Should the moisture content of this material reach between 5- 10% by
weight of the product, aerobic biological decomposition occurs, causing
self-heating. Water generated by this process is absorbed by the
surrounding sludge, which intensifies the self-heating process. A
smoldering fire may occur if the heat generated by this self-heating
process is not dissipated to the surroundings.

Processing and Handling

In the initial stages of sewage treatment, the digestion process
produces methane and carbon dioxide. If raw sludge is stored it will
decompose and produce hydrogen sulphide and other volatile sulpher
compounds. With the addition of chemicals to dewater the sludge,
hydrogen sulphide and ammonia may be released.
Conversion of sewage sludge into granules or pellets, by removing the
moisture, is the final stage of the sewage treatment process.
The amount of dust produced in the drying process and later processing
is affected by the method of drying and type of final product. Sewage
sludge dust is about the same size and similar hazard as wood dust.
Depending on the design of the plant, there is the potential for a dust
explosion to occur at the main dryer, dust collector and handling plant,
pelletizer and final product discharge plant.
In pellet form the product is sufficiently hard to withstand the normal
conditions of mixing, handling and transportation without producing
excessive levels of dust.
These pellets have a relatively low auto-ignition temperature, as low as
2650C, and may be easily ignited without process precautions.
A risk assessment followed by implementation of suitable prevention and
protection measures is required for all parts of the process. Special
attention should be given to the specific hazards associated with the
generation of methane, hydrogen suphide, and dusts. Appropriate
ventilation, relief venting, suppression systems, containment features,
avoidance of ignition sources, and safe handling and storage practices
also need to be considered.

Storage
Once dried, pellets may self-heat to the point of ignition and slow
burn. To minimize the potential for self-heating, sewage sludge pellets
should be kept cool and dry and should not be stored in large piles.
Storage silos should be designed to aid cooling and be sized to allow
thermal dissipation of heat. For this reason, tall narrow silos are
preferable to wide silos. Where significant levels of dust are likely to
be produced in the storage silos, they should be designed to mitigate
the effect of any explosion. The simplest protection is the provision of
explosion relief panels venting to a safe location.
Silos should be designed to identify and contain a fire. A slow burning
silo fire is likely to be starved of oxygen and therefore produce carbon
monoxide. A carbon monoxide detector in the silo will indicate an
incipient fire. As well, multi-point temperature probes may be installed
to monitor the temperature of the product. As an alternative to indoor
storage, pellets should be transported to a site location and be
off-loaded and turned into the soil as soon as possible.
If this is not possible, the material should be spread on the ground
evenly in the form of a very thin layer. This configuration will
dissipate any heat generated into the ground and atmosphere.


Fire suppression
Inside a silo, an inert gas can be used to contain, but not necessarily
extinguish, a fire. The injection of an inert gas will cause a drop in
temperature, but may only have a limited effect. The temperatures should
be monitored for several hours before deciding if the fire has been
controlled. Procedures to deal with a silo fire may include the gradual
emptying of the silo to a safe location.
Outside, a sewage sludge pellet fire typically smolders at the surface
with a relatively low burning temperature and emits dense white smoke
and products of incomplete combustion. The smoke may contain organic
acids and other compounds that are irritating agents. The simplest way
to deal with such a fire is to dissipate the heat by spreading out the
pellets. It may also be extinguished by confining and smothering.
Alternately, the pellets may be mixed into the soil or “stamped” with
heavy earth moving equipment.
In some cases, the use of Class A foam may be considered for fire
suppression. Class A foam is a special formulation of hydrocarbon
surfactants, that reduces the surface tension of water and provides for
better water penetration and increased effectiveness. Class A foam acts
as a surface barrier to stop or prevent further combustion.
The use of water to suppress this type of fire is controversial. The
application of water may actually support a fire by contributing to the
process of aerobic decomposition. Further, adding water may return the
dried sewage into liquid sewage and create additional leachate and
runoff. In turn, this may contaminate ground and surface waters
surrounding the site and could cause significant environmental and
health risks.
Overall, fire fighting tactics need to consider a range of
circumstances, not the least of which include the size of fire,
location, wind/weather conditions, water supply, personnel safety,
access to heavy equipment, and environmental impact.

Conclusions
Although fires involving sludge pellets are not common occurrences, they
do tend to attract a great deal of public attention and challenge the
fire service.
By working with the public, pellet factory owners, and owners of sites
used to spread sewage sludge pellets, the fire service can ensure that
safe practices are employed, thereby protecting the public, environment
and emergency responders.

Article prepared by OFM Fire Protection Engineers Beth Tate and Miles
Mailvaganam.