1. Silent Killer in a Newly Constructed Manhole

2. Reason For the Intervention
OSHA received notification of a construction site fatality on August 5, 2004 – day following the incident
Reported that the employee was found at the bottom of a manhole
New sewer system under construction - SIC Code 1623
The inspection was initiated after our office received notification of a construction site fatality from the employer on August 5, 2004, which was a day after the incident.
The report was that the employee was found at the bottom of a newly constructed manhole.
The employer was a small construction company with a total of 20 employees. The company installs water and sewer lines, with a SIC Code of 1623.

3. The Site
Company laying sewer pipe & manholes for a new housing development
6 employees onsite
Farm land; slightly hilly; slope of ground ~ 1 to 4
Manhole was adjacent to an entrance ramp to a highway
The employer was laying sewer pipe and manholes for a new housing development.
There were 6 employees on site the day of the incident - five of the employees were laying pipe over the hill from the manhole that was involved in the incident. One employee (the victim) was grouting the manhole.
This photo shows the manhole from top of the hill looking down.
The area was previously farm land, it was slightly hilly, and the manhole was placed in the terrain with a slope of 1 to 4.
The manhole was adjacent to entrance ramps to a highway.

4. 4 foot wide internal diameter
2 foot opening
4 foot wide internal diameter
Riser was constructed of 4’ X 4’ concrete pipe sections
17 feet deep outside 161/2 feet inside
Two 8” PVC Pipes in the bottom
Built on a 4” to 12” bed of limestone chat
This slide gives a break down of the sections of the manhole.
There were 4 sections with a total height of approximately 17 feet when measured on the outside (per drawings), and the inside measurement was 16 ½ feet (when measured with a trench pole). All of the sections were made of concrete and were coated with a water proofing substance. Ladder rungs were present in the interior surface.
There was a 2 foot opening at the top, and 4 foot wide internal diameter.
The manhole was set in a bed of gravel any where from 4 to 12 inches.
Two eight inch plastic sewer pipe enters and exits the manhole near the bottom.
At the time of the incident and the inspection activity, the inlets were plugged.

5. Code Requirements
City codes require a vacuum test – must maintain 10 inches of mercury for a specific time based on depth of manhole
If vacuum test fails, then sections of the manhole must be grouted to get a better seal
As stated earlier, there were 6 employees on site the day of the accident. 5 of the employees were working over the hill laying sewer pipe. The victim was assigned the job of grouting.
Each manhole, per city codes, must pass a leak test, which is accomplished by pulling a vacuum and the manhole must hold a vacuum of 10 inches of mercury for a set time based on the depth of the manhole.
This slide shows the vacuum test equipment. The upper photo shows the apparatus which seals the top of the manhole and the vacuum pump. The lower photo shows the plug inserts which are placed in the sewer pipe entering the bottom of the manhole and completes the sealed space.
If this test fails, as in this case, someone has to grout the seams of the manhole sections.

6. The Incident
After vacuum test failure, employee reportedly was assigned the grouting task
Grouting is done by hand and takes about 1 hour
The employee was working alone
The employee was found at the bottom of the manhole unconscious
After vacuum test failure, the employee reportedly was assigned the grouting task.
Grouting is often done by hand inside the manhole and it was reported that it takes about 1 hour to complete.
In this case, the employee was working alone in the manhole; and there was conflicting information as to when the last vacuum test was performed.
The employee was found unconscious at the bottom of the manhole.
The photo shows what OSHA found during the OSHA investigation—grout bucket and the orange hose connected to the plug inserts at the bottom of the manhole.
The plug inserts were still under pressure.

7. Manhole Conditions Inspection Activity
After recovery, the medical examiner requested sampling of manhole
Fire Department – Haz Mat Division took some multi-gas readings about 3 hours after recovery
Results were 16.3 to 17% for oxygen and 0.0 to 4.5 % LEL
Zero readings for carbon monoxide and hydrogen sulfide
No readings taken for carbon dioxide
Picture goes here
After recovery, the medical examiner requested air sampling of the manhole.
The Kansas City, Missouri Fire Department-Hazardous Materials (Haz Mat) Division arrived on site about 3 hours after recovery to perform the air sampling with direct read multi-gas instruments.
Results were recorded with two direct read instruments.
The oxygen levels were reported at 16.3 and 17%.
And LEL levels at 0.0 and 4.5% and Chlorine levels at 4 PPM.
There were no detections for carbon monoxide or hydrogen sulfide.
No readings were taken for carbon dioxide.

8. Inspection Activity
The employer did not have a confined space entry program
OSHA’s Salt Lake City Technical Center Health Response Team
assisted with site analysis
Direct Reading Instruments results 9 days later revealed:
Oxygen – 16.0 to 18.2 %
CO2 – 1.8 to 3.5 % or
18,000 to 35,000 PPM
LEL – 5 to 8 %
During the inspection, it was reported that the employer did not have a confined space entry program and no equipment available.
Our office requested the assistance from OSHA’s Salt Lake City Technical Centers Health Response Team who had assisted similar cases. They arrived on the site about 9 days after the accident. The manhole had not been disturbed other than the placement of the manhole lid. The plug inserts were still in place and were under pressure.
Air sampling was accomplished through direct read instruments including one for carbon dioxide levels and a multi-gas instrument for oxygen and LEL.
The levels obtained that day revealed 16.0 to 18.2 % oxygen; 1.8 to 3.5 % or 18,000 to 35,000 PPM for carbon dioxide; and 5 to 8 % LEL.

9. Inspection Activities (cont.)
Grab or bulk air samples taken with a medium flow pump at 3 L/Min.
Collected in aluminum bags
Lab results as follows:
Oxygen – 12.5 to 14.1 %
CO2 – 16,845 to 23, PPM
Methane – 776 to 1372 PPM
In addition, the Health response Team collected grab or bulk air samples which were sent to the lab for analyses.
The samples were collected in aluminum bags with a medium flow sampling pump, as seen in this photo, and set at 3 liters per minute.
There were four samples collected from the bottom of the manhole and one control sample which was taken outside of the manhole.
The results produced the ranges of 12.5 to 14.1 % oxygen; and roughly 17,000 to 24,000 PPM (16,845 to 23,968 PPM) Carbon Dioxide; and 776 to 1372 PPM Methane.
The control sample revealed 19.8 % oxygen and 349 PPM for Carbon Dioxide.
These results were comparable to the direct readings that were obtained by the fire department.
Another interesting note, was that during this sampling the owner of the company was on site and had borrowed a multi-gas instrument and was inserting the instrument into the manhole along side of OSHA’s equipment. The alarm would go off when the oxygen level was below the set level of that instrument which is usually at 19.5% or slightly higher.

10. Carbon Dioxide Colorless odorless gas Special problem in Midwest area
Displaces oxygen leading to oxygen deficiency
Special problem in Midwest area
Limestone Rock
Calcium Carbonate
Acidic topsoil
Acid leaches from soil, which then contacts the limestone producing Carbon Dioxide
Numerous fatalities
Especially in new sewer/vault leak testing using a vacuum
Pulls carbon dioxide into the space
Oxygen measured at less than 3% on other similar fatalities
5 similar cases known Nation-wide since 2000; 2 cases with 4 fatalities in the Kansas City area
In theory, what happens in these newly constructed manholes is the displacement of oxygen with other substances including carbon dioxide.
Carbon dioxide is a colorless and odorless gas and it is heavier than air.
In the midwest area, we have limestone rock and/or the manholes are constructed with a bed of limestone rock/gravel and there is acidic soil. It is believed that the acid leachs from the soil and combines with the limestone rock producing carbon dioxide.
There were 5 known cases involving fatalities in newly constructed manholes nation-wide since the year 2000, with 4 fatalities in the Kansas City Area. In most of these cases, the manholes were not connected to the active sewer (as in this case) and the vacuum test for leaks had been performed prior to the entry. It is believed that carbon dioxide is pulled into the manhole displacing the oxygen during these leak tests. The oxygen content in these manholes has been found to be as low as 3%. In most of the cases, it was reported that the employers have been entering the manholes for years without any problems; and manholes in the same areas had normal levels of oxygen and carbon dioxide.

11. Oxygen Deficient Atmospheres
19.5 % Minimum acceptable oxygen level.
% Decreased ability to work strenuously. Impair coordination. Early symptoms.
12-14% Respiration increases. Poor judgment.
10-12% Respiration labored. Lips blue.
8-10% Mental failure. Fainting, Nausea, Unconsciousness, Vomiting.
6-8% 4-5 minutes - possible recovery, 6 minutes - 50% fatal, & 8 minutes - fatal.
4-6% Coma almost instantaneously. Death
19.5% oxygen is the minimal acceptable oxygen level per definitions used by OSHA, such as that used in the permit-required confined space standard in general industy.
As the oxygen levels decrease and depending on the work activity and the individual consumption, it becomes more difficult to support body functions.