Fatality in Water Valve Manhole 7

[hairman]

Thursday August 14 at 12:00 a laborer entered a 17'6" deep by 6'diameter water valve manhole to operate the valve. He entered without checking the atmosphere and died despite heroic efforts of his coworkers.

Background:

The manhole had been installed three weeks ago as part of a new watermain installation. The manhole had rubber boots sealing the water main pentration and mastic sealing each joint of the manhole. The manhole was adjacent to a creek with the invert approximately 9 feet below the creek bed.

Approximately 2" of water had accumulated in the bottom of the manhole at the time of the accident. The relatively small amount of water may have entered from the surface or possibly by condensation, however, I think that inflitration from outside is unlikely since the manhole was installed in wet conditions and a leak would have probably resulted in much more water.

The accident:

Two workers were excercising valves on a new water system primarily with keys via stop boxes. One worker entered the manhole unbeknownst to the other worker. The second worker realized his partner had entered the manhole and went to investigate. The amount of time elapsed between the last time the workers had seen each other was approximately one minute. As the second worker looked into the manhole, he heard the victum say that he had to get out. The victum climbed to the third from the top step and fell back to the bottom of the manhole.

The top man called 911, and then called his coworkers. Coworkers arrived within a couple minutes with a compressor and began blowing air into the manhole. They also began monitoring the air with a four gas meter. Oxygen initially registered 13% about 8 feet below the manhole cover. By the time the emergency rescue personnel arrived (approximately 15 minutes) the air was reading around 20% oxygen. Flammables registered 0% LEL, CO registered 0 ppm, H2S registered 0 ppm.

The rescue personnel donned breating apparatus and entered the manhole to recover the victum. The victum was extricated from the manhole. CPR was administered, however, they were unable to revive the victum.

Follow-up investigation:

Four hours after the incident, the manhole was reopened and the air was monitored. 8 feet below the cover, the oxygen registered 15%, 15 feet below the cover the oxygen registered 5%. Flammables - 0 LEL. CO - 0 ppm. H2S - 0 ppm.

Questions:

1)What was the mechanism causing the oxygen deficiency?

2)How could the air become so deficient in oxygen so quickly after the manhole had been ventillated?

3)I intend to sample the water at the bottom of the manhole, what should I look for?

4)What other gasses should I try to get a meter to test for?

5)Any other ideas?

Thank-you for your time and input.
Harry G. Butler, P.E.

 

[fitz]

A tragic accident, and I want to express my sincere sympathy to the victim's family, his friends and his co-workers.

I'd say good training was the reason the other men didn't try to go into the manhole and rescue the first man.

My thoughts below are probably only some that have already occurred to you and people involved with the utility.

Perhaps the air blown into the manhole with the compressor didn't really displace the foul air completely and so later readings after getting the victim out of the manhole still represented what was in there to begin with.

I found an Internet page with a lengthy discussion of another death in a manhole, and the conclusion seems to be that it may have been the the man's own breathing that used-up the available oxygen and replaced it with CO2 at the bottom of that manhole. The site is at:

http://www.jacpe.com/consult/case7710.html

Or, perhaps there is some kind of "air" flow entering the manhole from below--probably not likely, but I suppose a possibility, say from some biological process producing CO2. Thinking of some gas entering the manhole makes me refer back to the Internet site which mentions the possibliity of CO2 from engine exhausts flowing into the manhole, displacing the air and remaining in the bottom of the manhole. If that is the case, it could have been in there for days.

Corrosion of iron can use-up oxygen pretty rapidly, but there was probably not much exposed iron in the manhole.

 

[fitz]

I forgot one other possiblity. Perhaps the victim collapsed not because of the atmosphere in the manhole, but because he was ill. He may have had undiagnosed heart trouble, or could have suffered a stroke.

 

[Bbird]

I knew an incidence some 30 years ago when 2 members of a sewerage gang died after entering a sewer. The first collapsed after entry and the second one died by trying to rescue the first. Poisonous gas from the sewerage was responsible for their deaths. The two apparently did not use the gas detector lamps provided as part of their equipment. I fully agree with fitz that others did the right thing by not entering the manhole to save the victim.

Recently I have to arrange inspection/maintenance work for a system of seawater culverts (total length 20km and not used for 16 years). I had to specify the removal of covers 2 manholes upstream and 2 manholes downstream at the point of entry for ventilation at least for 24 hours before any work was permitted. The work has been completed satisfactorily.

I couldn’t help with your detection work but let us learn from mistakes.

I suppose there could be other denser gas displacing the oxygen in the manhole. Natural ventilation does do much in your case unless the denser gases are forcibly expelled, as the water main manhole is a close environment.

 

[quark]

I would agree with fitz. Generally a person requires 16 cfm fresh air (i.e 0.2 x 16 = 3.2cfm of oxygen) to keep exhaled CO[sub]2[/sub]in control.

I agree with corrosion point also.

Check disolved oxygen in water.

Check for BOD.

I was told of similar incidence during start of my career and that is why I always check oxygen content before going inside tanks and reactors. Infact we have a confined entry work permit system which has some check points to fulfill before starting work.

 

[hairman]

Regarding the Dissolved Oxygen in the standing water: Today I took samples of the water at the bottom of the manhole. What should I test for with respect to disolved oxygen, and what other characteristics should I test for to find clues to the mechanisms for depletion of the oxygen.

Incidently, the manhole is currently registering 2.3% oxygen at the bottom of the manhole and 18.1% oxygen 4 feet below the top of the manhole.

Thanks to everyone for their input.
Harry G. Butler

 

[gtrainor]

Is this manhole located near vehicle traffic? If so, the gases from the exhaust are heavier than the surrounding air and will seek a low spot, such as a manhole. If vehicles or any kind of combustible engine is nearby, test the air in the manhole for CO2 and CO.

 

[quark]

First, you should check for CO[sub]2[/sub]. Checking Biological Oxygen Demand (BOD) will give you an idea about the bio growth in the water. Generally, the DO in water is about 4 ppm but it can be maximum 14 ppm. Check for increase in DO.

I mainly suspect bacteria and the accuracy of your meter.

If the volume is 170 cu.ft (3.142x6x6x6/4, consider 6' height of the person), the oxygen content will be 170 x 0.023= 3.91 cu.ft and it is quite sufficient for one minute.

But CO[sub]2[/sub]is heavier than O[sub]2[/sub] and this will not help much in diffusion.

I hope these vague thoughts will help you in someway or the other.

Regards,

 

[davefitz]

There should be available a gas testing device to determine the actual gas which is displacing the oxygen. Try contacting a testing lab, one which is normally testing the output from a chemical refinery or power plant stack.

 

[fvincent]

Should it be possible that a certain amount of de-gased CO2 (dissolved in water) could be leaking through valve sealing?



fvincent

 

[NRGGUY]

I suspect CO2 or CO - probably from either a surface (vehicle exhaust) or subsurface source (biological or chemical activity in surrounding soil). An autopsy should identify the mechanism and agent. Once the mechanism and agent is identified, the source should be fairly straight forward.

 

[KRSServices]

I'm going to be blunt and to the point. From your description this was a needless and totally preventable tragedy. Car exhaust, CO, were not the cause of death, and I do not need to see the results of an autopsy for this. The worker passed out due to oxygen deprivation and lack of training with respect to confined space entry.

While the previous threads are commendable, it is quite obvious that none of you have ever had confined space training, nor have ever had to purge a chamber, or enter one. Having spent the early part of my career working in valve chambers and manholes, I hope I can strike a nerve and be able to prevent ever hearing of another accident in this fashion.

The oxygen near the surface was 15% - that is way too low, and a detector will alarm at about 19%. 5% is lethal. The probable cause for the lack of oxygen is rust and corrosion. The lack of a competant safety program, enforcement and training killed this employee.

Please people, there are many documented cases where oxygen deprivation killed people so institute a confined space training. Ensure employees know how to properly purge the space. Purchase the monitors for the employees to wear or carry with them into the confined space. Most important....enforce the rules! If you want information, or advice as to some of the municipal and public works safety programs I have set up, please do not hesitate to contact me. I absolutely detest hearing about preventable accidents!

P.S. The same holds true for lock out procedures when working around machinery (pumps, belts, etc).

KRS Services

http://www.krs-services.com

 

[fvincent]

Considering the following excerpt:
"
Coworkers ...began blowing air into the manhole...Oxygen initially registered 13% about 8 feet below the manhole cover. By the time the emergency rescue personnel arrived (approximately 15 minutes) the air was reading around 20% oxygen.
...
Four hours after the incident, the manhole was reopened and the air was monitored. 8 feet below the cover, the oxygen registered 15%, 15 feet below the cover the oxygen registered 5%. Flammables - 0 LEL. CO - 0 ppm. H2S - 0 ppm.
"
I would guess a relatively high rate source of other gases was present...and not O2 depletion...



fvincent

 

[KRSServices]

The monitor should be detecting the presence of CO and oxygen, among other things. The importance is the fact that after four hours, the level of oxygen at the upper level was near lethal. It does not matter that the O2 is reacting with another gas or being converted or used, the fact remains that the O2 levels were lethal. It is a confined space, and that means the individual should have been harnessed, monitored and the chamber continuously purged with fresh air, period! It does not matter whether this is a manhole, valve chamber, empty tank, cargo hold, lift station wet well, or large diameter pipe. If the space is defined as confined, the employer and employees should have followed the rules. If this employee was properly harnessed, it is possible that a rescue could have eliminated the fatality.

According to the thread, O2 was rapidly being depleted. there could be any number or combination of biological processes that contributed to that depletion within the chamber. Everybody, please use this as a wakeup call. I've lost employees to stupid safety mistakes or oversights, you know, the "only if" or the "it would only have taken two extra seconds" mistakes, so I personally know what that organization is going through.

KRS Services

http://www.krs-services.com

 

[BRIS]

Are all chambers on potable water installations classified as confined spaces?

Before entering any chamber a risk assessment should be undertaken but the fact that it is a below ground chamber will not automatically classify the space as a confined space requiring gas monitoring before entry. (or will it?).

As a general safety requirement, regardless of whether the chamber is classified as a confined space, any person descending into a chamber should wear a safety harness and have a safety line.

 

[KRSServices]

Confined Space is defined as:

"An enclosed or partially enclosed space having restricted access and which, due to its design, construction, location, atmosphere, the materials or substances in it or other conditions, is or may become hazardous to a worker entering it or does not have an easy means of escape for or rescue of a worker entering it."

Confined spaces include, but are not limited to, manholes, chambers, new manholes, lift stations where a worker must access or egress via a ladder or steps and fresh air is not blown or circulated, wet wells, dry wells, tanks and vessels and large diameter water pipes. A 2,000,000 litre underground reservoir can be classified as a confined space if the access and egress (through a hatch) is the method employed by the worker and will require constant atmospheric monitoring and a harness.

To accurately answer BRIS's question. Pretty much all municipal water and sewer infrastructure can be classified as confined spaces because of their very nature of being buried, thence requiring manholes, chambers or deep pumping facilities.

KRS Services

http://www.krs-services.com

 

[cvg]

KRS is correct, and all of this can be found very easily on the OSHA website.

http://www.osha-slc.gov/doc/outreachtraining/htmlfiles/cspace.html

 

[hairman]

I have further factual information regarding the atmosphere in the water valve manhole. On August 21, 2003, several safety experts returned to the scene of the accident with gas monitors including a CO2 monitor that had been factory calibrated. Readings were as follows:

2' below the cover O2 - 16.5% CO2 - 6.7% LEL - 0%
CO - 0 ppm H2S - 0 ppm

8' below the cover O2 - 1% CO2 - 8.8% LEL - 4%
CO - 0 ppm H2S - 0 ppm

12' below the cover O2 - 1.5% CO2 - 8.7% LEL - 5%
CO = 0 ppm H2S - 0 ppm

Please refer to the original post of this string.

Questions:

1) What mechanisms are there that could have depleted the oxygen?

2) Could processes that occurred outside the manhole (oxidation of iron in the soil or decomposition of organic material) have affected the atmosphere in the manhole?

Finally, regarding KRS Services comments, KRS has made some huge leaps to conclusions without knowing anything about the victum's company's training program, entry procedures, or enforcement program. I am searching for some answers that may help companies understand the hazard and hopefully prevent this type of incident in the future. So, KRS, if you have some information that could contribute to the questions at hand, please let me hear from you. Otherwise, please start another string for your editorial comments.

 

[KRSServices]

hairman,

If I have offended you, I'm not sorry! Regarding your thread, I leap to no conclusions nor was I being editorial. You want specific reasons, the followup inquiry to the fatality will provide those. You are making a very serious mistake if by learning that some specific process was responsible for the oxygen deficiency. Every confined space is a hazard. Did you know that a vault near a treatment plant can contain lethal amounts of chlorine gas, which is heavier than air? If a worker had a monitor, it would be identified as a lethal environment without ever entering the space.

You want answers so that the accident can be prevented in the future, then begin by educating yourself and others about workplace hazards, in this case confined space.

It does not really matter that the oxygen levels in the vault were fatal. The company either did not educate it's workers or was not educated itself and I'm not preaching here!

I do not have to be in the City or reviewing the company policy to know that a vault, any vault, is confined space and therefore a hazard. That means a monitor is required at the very least. If the worker was trained properly, it NEVER would have happened. Now, you can either be proactive or continue to chastise me, but either way if you intend on ignoring the actual significant contribution to the fatality and seek out another explanation that would explain the science behind the lethal atmosphere, then you are setting yourself up for another disaster.

I have my certification in confined space entry, as did ALL my employees. It only takes two hours and will save thier lives, regardless of industry. Please insist or at least recommend that this training be instituted firstly, then worry about the actual whys later.

Finally, did you know that three employees were killed by oxygen depletion in a cargo hold of a ship in Vancouver, did you know that two employees were killed due to oxygene depletion in a live sanitary manhole, one was a rescuing firefighter, did you know that a worker was overcome in a cleaned water reservior due to the oxygen reacting with the cleaning agent? I'm not trying to chastise anyone here but properly recognizing the hazard (vault - confined space) would have saved the employee his life!



KRS Services

http://www.krs-services.com

 

[fvincent]

hairman,

As I have asked before:
"Should it be possible that a certain amount of de-gased CO2 (dissolved in water) could be leaking through valve sealing?"








fvincent