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.

 

[johnd43]

Words can't express the sorrow we all feel whenever we hear of such events. I could not add to any of the sound advice about understanding the dangers and doing the training to eliminate the consequences of these hazards. But I can remind you of a few items from recent engineering history.

Yes, gases do suffuse through apparently solid containments.

We had an accident here in UK about 20 years ago caused by methane escaping from coal measures very deep below a river water transfer project. Apologies to those who know better if I have miss-remembered some details. As I recall, the pipeline passed hundreds (?) of feet above the coal but it still captured the gas and transferred it to the terminal structure where it accumulated, despite measures to ventilate the chamber, until it got the chance to ignite. The explosion demolished the structure and killed several people, injuring many more.

I believe this was one of those seminal incidents that started to focus us on the subject of confined spaces and reverse the general assumption that all would be ok. As a result of these tragedies we have very strong Health and Safety legislation in UK, but we still have a dreadful number of accidents every year.

In a completely different vein, we have problems in some parts of UK with radon gas being emitted from deep granite bedrock at sufficient rate to cause problems in housing sited above these strata. One wonders why, if it will rise through huge depths of granite, it doesn't go straight through a few bricks and mortar? But it doesn't and special measures have to be implemented.

And on the subject of CO2, it is a very small molecule which can pass through membranes that will retain other gases. When you blow up a party balloon, you will see that it deflates over the following period. This is the CO2 component that is escaping, whereas the residual oxygen and nitrogen that have been puffed in are both retained. If you use a pump and atmospheric air, the ballon stays up much longer.

I can recall press coverage of a number of fatal accidents that resembled the original tagedy described in this string. One was in the toe drain of a relatively new earthfill dam - no metals and not particularly deep as I recall. I am pretty sure ambient CO2 was the culprit, but in some respects that is beside the point, as KRS has commented. I do recall that at least one of the dead was the true freind who went into danger to help his co-worker.

I apologise again - to anyone feels these are trivial comments and out of context here - but I feel as strongly as KRS that we must learn all the lessons, and not let our thinking be confined by any one set of circumstances. Explosive and toxic atmospheres can be as dangerous as asphyxiating atmospheres and Pumpdesigner's contribution shows how important it is to spread understanding of these very serious risks.

 

[labster]

First let me say that this is a great discussion to be having.

In our municpality, we train in confined areas, that from the lay persons view would never suspect that there were atmosphere issues.

Two months ago, we placed a manikin in our favorite valve manhole and called 911 for a moch training emergency. Fire personnel responded, and started down the confined space without a permit testing of the atmosphere or SCBA. They never suspected that there was anything wrong with the atmosphere. They were shocked when we stopped the drill and monitored the atmosphere.

As a supervisor for confined space entry, I must state that KRS Services has stated the issues correctly. While not trying to rub salt in the wound I am concerned about a potential safety problem in the making...

We too try to identify what is causing a specific atmosphere to be dangerous. Often times we are able to lay our hands on the problem and correct what may be causing the issues. However, please note that I see the tendency in the work place to ignore the variables that may affect an atmosphere after a specific cause has been identified and corrected.

The best example is sanitary sewer manholes. For the first 10 minutes a crew is performing work the atmosphere is acceptable. They tned to relax and go about there work with a little less concern. Only to find out that the house up the street has just poured carpet cleaner down the drain. Low an behold the atmosphere heads south.

While I applaud your efforts to identify the source, there is ALWAYS the need to monitor; and ventilate if the atmosphere is not acceptable. Ventilation should include a powered blower to insure that the worker(s) are receiving a fresh flow of air.

Bottom line..it really is not the answer to know what caused the atmosphere issue, since what caused the problem 10 minutes ago may not be the same issue that kills you 10 minutes after the atmosphere re-checked okay.

Regards