03/18/03
Filter Fires!
Permissible
Equipment
The installation of combustible (generally paper)
filters on permissible equipment can increase the likelihood of fires. Other Best Practices have discussed the hazard
of hot surfaces from the addition of filter piping and housings and the
potential for uncontrolled regeneration (fire) in a ceramic filter on
nonpermissible equipment. However, even
on temperature controlled permissible equipment filter fires can and have
occurred. Filter fires on permissible
equipment can result in catastrophic consequences and must be prevented.
Filter fires on permissible equipment are primarily
the result of the failure to maintain the safety features provided on this
equipment. These failures may be rooted
in designs that use components with poor reliability. The failure of the safety system creates a fire and explosion
hazard regardless of whether a filter is installed. The consequences of a filter fire, however, are more apparent and
are much more likely to have catastrophic consequences compared to just the
release of exhaust gases at high temperatures.
In addition to a clear failure of the safety system, a delay in engine
shutdown resulting from an out-of-calibration sensor can also result in a
filter fire.
A failure of the safety system can result in a fire or explosion.
The safety systems on 30 CFR part 36 permissible equipment are
not designed to be totally fail-safe, but they do incorporate a number of
fail-safe features. They have redundant temperature sensors,
spring controlled fuel rack shutdowns, and an automatic shutdown on loss of
safety system air or hydraulic pressure.
However, multiple defective sensors, out-of-calibration sensors, and
willfully disabling the safety system can lead to filter fires and catastrophic
consequences. Also, failures of
components that are not fail-safe, such as pressure regulators (not limiting pressure
to the safety system) and fuel racks (hang ups) can cause the safety system to
fail.
MSHA evaluates the design of safety systems during
the approval process to ensure the safety system is well designed and meets the
applicable regulations. Regulations also specify weekly maintenance checks and shift maintenance checks that must
be performed by the mine operator to ensure the system functions as designed
over the life of the machine. MSHA had
considered that these tools were sufficient to prevent filter fires. Continued reports of filter fires brings
this into question. MSHA
requests mine operators notify MSHA of any filter fires. MSHA recommends the following:
Action Items-
!
Perform regular maintenance. If safety system failures are frequently
found during weekly checks then daily checks, improved training, or contacting
MSHA and the equipment manufacturer may be required. MSHA inspectors will focus additional attention on the
performance of safety systems.
!
Do not jumper-out the safety system. If the safety system needs to be by-passed
for maintenance it can
only be by-passed in areas of the mine where nonpermissible equipment can be
used and in accordance with a written procedure developed in consultation with
the equipment manufacturer.
!
Train machine operators and other mine personnel how
to respond to filter fires. Review the
fire risk assessment of the machine to determine if fire suppressant coverage
of the filter element is necessary.
!
MSHA will contact equipment manufactures to discuss
the need to revise the approval requirements to improve the reliability of
safety systems and whether higher levels of maintenance should be
required. MSHA encourages mine
operators discuss reliability and maintenance concerns with the equipment
manufacturer.
!
Do not use combustible filters until other means
(such as increased maintenance, higher reliability components, or fail-safe
system designs) are proven to prevent fires.
Use fire resistant filters. Reference Micro Fresh
Filters
and EIMCO LLC.
!
MSHA is evaluating new ways for preventing filter
fires. These currently include faster
reacting and more reliable temperature sensors, tamper-resistant shut down
systems, and low scrubber water warning systems.
Reference: Diesel
Faults/Causes List, and Failure Analysis of Diesel Exhaust-Gas Water Scrubbers, hardcopy available upon request.
