|NIOSH In-house FACE Report 2004-09
May 19, 2005
On May 17, 2004, a 36-year-old Hispanic laborer (the victim) died after
he entered a sawdust storage silo to unclog a sweep auger advance mechanism
and became engulfed in sawdust. Several minutes after the victim entered
the silo, a Hispanic coworker working nearby heard a noise from the silo
which prompted him to call out to the victim. When he heard no response,
he and several Hispanic co-workers began looking for the victim. After
approximately 20 minutes of digging through the collapsed sawdust, they
found him. Coworkers ran to several locations trying to report the incident
and get help. They notified a company senior official who then called
911. Emergency Medical Services (EMS) responded within approximately 30-35
minutes of the presumed time of engulfment and attempted resuscitation.
They transported the victim by ambulance to a local hospital where he
was pronounced dead by the emergency room physician.
NIOSH investigators concluded that, to help prevent similar occurrences,
- ensure that equipment is inspected daily and all defective equipment
is removed from service until needed repairs have been made
- consider retrofitting silos and similar storage facilities with mechanical
leveling/raking devices or other means to minimize the need for workers
- develop, implement, and enforce a comprehensive written safety and
training program for all workers, including requirements for work in
permit-required confined spaces, such as silos
- train workers in hazard recognition and safe work practices for all
tasks to which they are assigned or allowed to perform, including those
pertaining to work in permit-required confined spaces. The use of the
workers’ primary language(s) and careful consideration of literacy
levels will maximize worker comprehension of these subjects.
- post warning signs at entrances to permit-required confined spaces,
such as silos, warning of immediate danger and safety requirements for
entry in a language(s) that all workers can understand.
On May 17, 2004, a 36-year-old Hispanic laborer (the victim) entered
a sawdust storage silo through an opening under the silo floor to unclog
a sweep auger advance mechanism. As he worked, sawdust, piled as high
as 30 feet up the wall of the silo, collapsed and engulfed him. On August
12, 2004, the North Carolina Occupational Safety and Health (NCOSH) office
notified the National Institute for Occupational Safety and Health (NIOSH),
Division of Safety Research (DSR) of the incident. On August 19, 2004,
a DSR safety and occupational health team conducted an investigation of
the incident. The incident was reviewed with the NCOSH compliance officers
who had conducted an incident investigation on the day of the incident,
and a site visit was arranged. One of the company’s senior officials
and their environmental health and safety (EHS) manager accompanied DSR
investigators to the incident scene where an inspection was conducted
and photographs were taken. Investigators reviewed the sheriff’s
report and obtained the cause of death from the medical examiner’s
The employer purchased the sawmill in 1986 and employed 142 workers.
Approximately half of these workers were Hispanic. The victim was Hispanic
and had been working at the facility for more than a year. He spoke primarily
Spanish, but reportedly was able to understand basic work instructions
given in English. Reportedly, supervisors spoke English but were able
to give basic work instructions in both Spanish and English. Three weeks
prior to the incident, the company had hired an experienced EHS manager,
a position that had not been filled for nearly 4 years. According to the
NCOSH compliance officer, the company had a general safety program that
was deficient in several areas. The confined space and hazardous energy
programs in place at the time of the incident were not adequate for this
facility. The confined space program consisted of a video in English entitled
“7-Minute Safety Trainer Program on Employees’ Roles in Confined
Spaces.” The video was sent home with some of the employees to be
watched at home. There was no documentation indicating that the victim,
or a coworker removing sawdust on the day of the incident, had received
training in safe work practices when working in or around confined spaces
or around hazardous energy. The newly hired EHS manager was developing
more comprehensive confined space and hazardous energy programs, but these
had not been completed and implemented. This was the employer’s
first workplace fatality.
The incident took place at a sawmill that produced over 35 million board-feet
of saw lumber per year. On site were three silos that were used to store
sawdust, a by-product of lumber processing. Two of these silos, including
the one involved in the incident, were flat-bottomed silos (photo
1). They had been purchased used at an auction, and were installed
approximately one year prior to the incident. The third silo was an older
hopper-bottomed design and had been manufactured by a different manufacturer
The silos received sawdust from the mill through a blower system. The
sawdust was stored there until it was needed to fuel boilers. Whenever
the local electric utility was unable to meet the mill’s energy
needs, sawdust would be moved from the storage silos to the boilers using
a system of augers. When sawdust was burned to heat water in boilers,
steam heat was generated and converted to electricity on site to run the
According to the company’s senior official and the company’s
EHS manager who accompanied DSR investigators to the incident site, the
sweep auger system in the flat-bottomed silos had clogged frequently since
the time it was installed, and required unclogging approximately every
two weeks during the periods it was activated. The victim was working
inside one of these silos, which measure 30 feet in diameter, 60 feet
in height and have flat, level floors, when he became engulfed in sawdust.
A three-armed rotating sweep-auger installed on the silo floor was used
to funnel the stored sawdust through an opening in the middle of the silo
floor. The sawdust would then fall down to another auger called a transfer
unloader located below the silo floor in the machine room (photos
3 & 4). The transfer unloader auger would
then funnel the sawdust through a series of pipes to the boilers (photo
5). The machine room contained the power equipment to operate the
augers and serves as a storage site for other pieces of equipment.
The company’s written procedure for manually unclogging the sweep
auger advance mechanism (reproduced below verbatim in its entirety) reads
Clean out Procedures for the Silos
- Remove 3 12 x 24” access doors.
- Chip away card board at the access door.
- Take poles and rakes and chip away at the saw dust. (Photo
- Repeat step #3 until saw dust is below the first ring level before
entering into upper level of silo.
- Lockout disconnect and finish cleaning out silo from inside.
- Repair and test.
The written procedure above implies that the workers were to remain positioned
inside the auger machinery room, not inside the silo, until sawdust
was “raked down” to below the predetermined depth (“below
the first ring”). No instructions were available in Spanish.
On the day of the incident, sawdust in the storage silo was to be removed
in order to unclog the sweep auger located on the silo floor. One Hispanic
laborer entered the silo from the machine room directly below the silo
floor through the access opening (photos 7 &
8), but quickly exited after determining that the
conditions were unsafe inside the silo due to the tall mounds of sawdust
against the silo walls. According to another Hispanic laborer, the victim
entered the silo alone a short time later to remove sawdust to clear the
sweep auger. A coworker reported that the victim had been warned previously
by at least two coworkers in both Spanish and English about the unsafe
conditions. As the victim worked, sawdust piled as high as 30 feet up
the wall of the silo collapsed and engulfed him not long after he entered
the silo. Several minutes passed before his absence was noted by coworkers
who then began calling out to the victim. When there was no response,
one coworker climbed to the top of the silo in order to take a look from
above. He did not see the victim. By this time, other coworkers entered
the silo and, manually digging and using poles for probing, searched for
the victim in the collapsed sawdust.
Coworkers found the unresponsive victim after approximately twenty minutes
and tried to remove the sawdust from his mouth. Coworkers ran to several
locations trying to report the incident and get help. A company senior
official was notified of the incident and called 911. However, the call
for 911 was not placed until the victim was already found. Emergency Medical
Services (EMS) responded within 30-35 minutes of the presumed time of
engulfment and attempted resuscitation. EMS transported the victim by
ambulance to a local hospital where he was pronounced dead by the emergency
After the incident, the flat-bottomed silos were shut down. The hopper-bottomed
silo had no history of jamming and remained in operation.
Cause of Death
The medical examiner’s report indicated the cause of death was
Recommendation #1: Employers should ensure that equipment is inspected
daily and all defective equipment is removed from service until needed
repairs have been made.
Discussion: Employers should designate a supervisor to be responsible
for daily preshift equipment checks and for verifying that any problems
identified are corrected. Although equipment may also be inspected by
other workers, for example, the workers assigned to begin the sawdust
transfer to the boiler, the supervisor must be responsible for ensuring
that inspections are performed daily, that necessary repairs are made,
that scheduled maintenance is performed, and that records of all inspections
are maintained. Equipment not operating properly should be removed from
service until repairs are made. All sources of hazardous energy should
be locked out before any repairs are begun. Regulations regarding the
control of hazardous energy (lockout/tagout) must be followed and are
covered under the OSHA standards.1
Recommendation #2: Employers and manufacturers should consider retrofitting
silos and other similar storage facilities with mechanical leveling/raking
devices or other means to minimize the need for workers to enter.
Discussion: Company owners should consult with silo manufacturers to
determine which measures would improve the flow of the materials. Silos,
bins, and hoppers where loose materials such as waste sawdust are stored,
handled, or transferred could be equipped with mechanical leveling/raking
devices or other means for remotely handling materials. These devices,
such as mechanical agitators or vibrators, could minimize or eliminate
the need for workers to enter such storage facilities.
An expert in engulfment and silo operation was contacted and told DSR
investigators that materials such as sawdust are more prone to “bridging”
than other granular material.2 Bridging
occurs when sawdust in the silo forms a thick, hard crust on the upper
portions including the surface. As sawdust is removed from below, a hollow
cavity is formed and some sawdust remains suspended above this cavity.
This could explain the reason for the sawdust piling up and clinging to
the interior walls of the silo. With the use of hopper-bottomed silos
or the addition of mechanical devices such as bin vibrators, sawdust buildup
would be limited, and workers would not need to enter the silo. In this
way, exposure to mechanical and engulfment hazards inside the silo could
Recommendation #3: Employers should develop, implement, and enforce a
comprehensive written safety program for all workers, including requirements
for work in permit-required confined spaces, such as silos.
Discussion: Although employees had received some on-the-job training,
they had not received adequate training based on OSHA requirements for
a permit-required confined space program. The Occupational Safety and
Health Administration standards define a permit-required confined space
as a confined space that has one or more of the following characteristics:
- Contains or has a potential to contain a hazardous atmosphere;
- Contains a material that has the potential for engulfing an entrant;
- Has an internal configuration such that an entrant could be trapped
or asphyxiated by inwardly converging walls or by a floor which slopes
downward and tapers to a smaller cross-section; or
- Contains any other recognized serious safety or health hazard.3
A permit-required confined space program has detailed requirements including,
but no limited to:
- implementation of measures necessary to prevent
- identification and evaluation of hazards of permit
spaces before entering;
- development and implementation of the means, procedures,
and practices necessary for safe permit space entry operations;
- providing of equipment for testing, monitor, ventilating,
communication, lighting, etc.;
- evaluation of permit spaces conditions when entry
operations are conducted.For a complete list of requirements for written
programs, see 29 CFR 1910.146 and OSHA Publication 3138.3,
The victim’s employer had procedures in place for removing sawdust
from inside the silo which allowed workers to enter the silo, a permit-required
confined space, without following the strict safety procedures required
by OSHA to protect workers in these types of permit spaces.
Employers should identify all permit-required confined spaces in their
facilities and compare their safety procedures against the minimum safety
requirements found in OSHA standard 29 CFR 1910.146 and make any changes
needed to ensure that their programs meet all of these requirements. All
employees who work in or around permit-required confined spaces should
be aware of potential hazards (e.g., engulfment; mechanical, electrical
or other injury hazards; oxygen deficiency; and presence of toxic or explosive
gases) possible emergencies, and specific procedures to be followed prior
to working in a permit-required confined space. These procedures should
include, but not be limited to:
- ensuring that the atmosphere is free of contaminants
and contains a safe level of oxygen
- identifying and controlling of the hazards associated
with unstable surfaces
- identifying and controlling other hazards, such
as mechanical or electrical hazards
- training employees in permit-required confined
space entry, testing, and the use of personal protective equipment,
safety harnesses, respirators, clothing, etc.
- stationing (a) stand-by person(s) outside the
space for communication and visual monitoring
- providing for emergency rescue procedures.3
Even though there were no dangerous air contaminants in the permit-required
confined space involved in this incident, entry into a permit-required
confined space should not be attempted until atmospheric testing of the
confined space ensures that the atmosphere is safe. This testing requirement
applies to all permit-required confined spaces. Testing must be done by
a qualified person prior to entry. Employers are required to follow OSHA
standards for all permit-required confined space entries.
Additional recommendations regarding safe work practices in confined
spaces can be found in the NIOSH Publication No. 80-106, Criteria
for a Recommended Standard: Working in Confined Spaces;5
NIOSH Alert Publication 86-110, Request for Assistance in Preventing
Occupational Fatalities in Confined Spaces;6
NIOSH Publication No. 87-113 A Guide to Safety in Confined Spaces;7
and NIOSH Publication No. 94-103, Worker Deaths in Confined Spaces:
A Summary of NIOSH Surveillance and Investigative Findings.8
These publications can be useful in developing confined space safety programs
and in training workers as they define hazards found in confined spaces
and provide recommendations for ventilation, communication, entry and
rescue, posted warning sings, required safety equipment, clothing, etc.
These NIOSH publications are available through the NIOSH web site at http://www.cdc.gov/niosh/topics/confinedspace/
or by calling 1-800-356-4674. (Link Updated 3/14/2013)
Despite the hazards involved in this operation, no pre-planning for any
type of rescue operation had been made. According to 29 CFR 1910.146 (d)(9),
employers are required to “develop and implement procedures for
summoning rescue and emergency services, for rescuing entrants from permit
spaces, for providing necessary emergency services to rescued employees,
and for preventing unauthorized personnel from attempting a rescue.”
Consideration should be given to inviting local rescue and emergency services
to survey the work site to evaluate and record locations of potentially
hazardous areas such as confined spaces. Requirements to develop and implement
procedures for summoning rescue/emergency services and for rescuing entrants
from permit spaces are found in 29 CFR 1910.146 (k).3
Recommendation #4: Employers should train workers in hazard recognition
and safe work practices for all tasks to which they are assigned or allowed
to perform, including those pertaining to work in permit-required confined
spaces. The use of the workers’ primary language(s) and careful
consideration of literacy levels will maximize worker comprehension of
Discussion: One of the workers had some training in confined spaces and
had warned the victim not to enter the silo. Another worker stated that
he had not received any training in confined spaces. At the time of the
incident, the newly hired EHS manager was in the process of updating the
company’s safety program. Employers must ensure that training is
done in accordance with current OSHA standards and with careful consideration
for the workers’ primary language(s) and literacy levels. Re-training
is recommended at regular intervals. If workers cannot read posted warning
signs, they should be given verbal instructions about what each sign means
and what procedures they are to follow when working in posted areas. An
interpreter should be used if workers require assistance in understanding
safety training. The use of posted warning signs does not preclude the
need for developing and implementing a confined space entry program including
proper and effective training.
For further information on permit-required confined space programs, employers
can visit the OSHA web site (https://www.osha.gov)
or call an area OSHA office for assistance to ensure that safety programs
meet required safety standards.
Recommendation#5: Employers should post warning signs at entrances to
permit-required confined spaces, such as silos, warning of immediate danger
and safety requirements for entry in a language(s) that all workers can
Discussion: Employers should post warning signs in the primary languages
used by their workforce and post them at the entrance to any permit-required
confined space at the workplace. Employers should refer to ANSI standards
Z53.19 and Z535.210,
and OSHA standards 1910.14511 for guidance
on requirements for safety signs. The following examples are warning signs
printed in both English and Spanish:
When employers post signs at entrances to permit-required confined spaces
warning of immediate danger and that special requirements are necessary
for entry in the primary language used by their employees, they increase
the likelihood that workers will be able to comprehend the procedures
they are to follow and be alert to possible danger. The meaning of these
signs and their location throughout the facility should be incorporated
into the company’s permit-required confined space training program.
The use of posted warning signs does not preclude the need for developing
and implementing a confined space entry program including proper and effective
- Code of Federal Regulations . 29 CFR 1910.147. The control of
hazardous energy (lockout/tagout). Washington DC: U.S. Government Printing
Office, Office of the Federal Register.
- D. M. Kingman (personal communication. September 27, 2004).
- Code of Federal Regulations . 29 CFR 1910.146. Permit-required
confined spaces. Washington DC: U.S. Government Printing Office, Office
of the Federal Register.
- OSHA . Permit-required confined spaces. Occupational Safety
and Health Administration (OSHA) Publication No. 3138-01R 2004. Accessed
on April 29, 2005 https://www.osha.gov/Publications/osha3138.pdf.
- NIOSH . Criteria for a recommended standard: Working
in Confined Spaces. Cincinnati, OH: U.S. Department of Health, Education,
and Welfare, Public Health Service, Centers for Disease Control, National
Institute for Occupational Safety and Health, DHEW (NIOSH) Publication
- NIOSH . NIOSH Alert:
Request for assistance in preventing occupational fatalities in confined
spaces. Cincinnati, OH: U.S. Department of Health and Human Services,
Public Health Service, Centers for Disease Control, National Institute
for Occupational Safety and Health, DHHS (NIOSH) Publication No. 86-110.
- NIOSH . A
guide to safety in confined paces. Cincinnati, OH: U.S. Department
of Health and Human Services, Public Health Service, Centers for Disease
Control, National Institute for Occupational Safety and Health, DHHS
(NIOSH) Publication No. 87-113.
- NIOSH . Worker
deaths in confined spaces: A summary of NIOSH surveillance and investigative
findings. Cincinnati, OH: U.S. Department of Health and Human Services,
Public Health Service, Centers for Disease Control and Prevention, National
Institute for Occupational Safety and Health, DHHS (NIOSH) Publication
- ANSI . American National Standard: Safety color coding for marking
physical hazards. New York, NY: American National Standards Institute,
Inc. ANSI Z53.1-1979.
- ANSI . American National Standard: Environmental and facility
safety signs. New York, NY: American National Standards Institute, Inc.
- Code of Federal Regulations . 29 CFR 1910.145. Specifications
for accident prevention signs and tags. Washington DC: U.S. Government
Printing Office, Office of the Federal Register.
This investigation was conducted by Gerard deGuzman, M.D., Occupational
Medicine Resident at West Virginia University School of Medicine assigned
to NIOSH, Division of Safety Research, Special Studies Team and Doloris
N. Higgins, Safety and Occupational Health Specialist, Fatality Investigations
Team, Surveillance and Field Investigations Branch, Division of Safety
Research. Douglas M. Kingman, Ph.D., from Illinois State University provided
additional expertise in engulfment and silo design and operation.
Photo 1. Silo in which fatality occurred. A) Door into the
silo machinery room.
|Photo 2. A) Hopper-bottomed silo model stored
and transferred the sawdust without clogging. B) Flat-bottomed silo
with exposed, partially disassembled, transfer unloader auger.
3. Power unit for augers. A) Sweep
auger axle: note that the cover plate is
removed and placed below the opening.
B) Pipe enclosing transfer unloader auger.
4. A)Sweep and transfer unloader auger
power unit. B) Transfer unloader auger, top
plates removed, loaded with sawdust.
Photo 5. Partially disassembled transfer unloader
auger system exiting the silo.
|Photo 6. Long-handled tool used by
laborers to chip cardboard and “rake down” sawdust from
the silo directly onto the uncovered transfer auger.
7. Silo floor as seen from the machinery
room. A)Overhead entry portal into the silo
with cover plate removed. B) Transfer unloader
8. Overhead entry portal with cover in place.