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harpa  
#1 Posted : 29 March 2018 14:21:25(UTC)
Rank: Forum user
harpa

Hi All, On the project I'm involved in we are undertaking significant earthworks that will lead to some deep (and wide) excavations of 20-30 metres. It has been suggested that there has been examples in the past from the quarry industry of carbon dioxide poisoning due to the amount vehicles working around the quarry and the fact CO2 is 1.5 denser than air. I'll admit i am initially slightly skeptical this may be an 'industry myth', however it has been raised in good faith so I thought I would follow up and at least be able to provide a response. I've done the usually searching to see if I can find any reports/lessons learnt but to no avail. Does anyone have any experience or knowledge of this as an issue to be mindful of? Many Thanks Paul
DaveBridle  
#2 Posted : 29 March 2018 14:51:11(UTC)
Rank: Forum user
DaveBridle

Might be worth having a look at this first:

http://forum.iosh.co.uk/posts/m617114-GAS-DETECTION-IN-TRENCHES

DaveBridle  
#3 Posted : 29 March 2018 15:06:09(UTC)
Rank: Forum user
DaveBridle

Forgot to add that you may also like to have a look at the HSE Guidance on diesel emmissions (INDG286).

http://www.hse.gov.uk/pubns/indg286.pdf

andrewcl  
#4 Posted : 05 April 2018 11:07:31(UTC)
Rank: Forum user
andrewcl

Carbon Dioxide is heavier than air - True

Carbon Dioxide has a Time Weighted Average (TWA - exposure over 8 hours) of about 0.5% - True

Carbon Dioxide has a Short Term Exposure Limit (STEL - exposure over 15 minutes) of about 1.5% - True

All these things combined with the wrong work place could mean you need to keep an eye on it.  How deep will the excavations be? How good will the (natural) ventilation be? How many engines are going to be running in the excavation? Are they running for 8 hour shifts, or 12 hour shifts? Is it reasonably practicable (that is not too expensive...?!) to do a 3 or 4 minute atmosphere test for CO2 before letting them on the tools?

Chances are it will be treated as a Confined Space anyway, simply because of the potential for free flowing solids, why not do an atmosphere test at the start as well, if only to reassure whoever asked you about this...?

Kate  
#5 Posted : 06 April 2018 11:28:12(UTC)
Rank: Super forum user
Kate

This is a genuine question for my information.

Wouldn't you be more worried about carbon monoxide?

descarte8  
#6 Posted : 09 April 2018 12:21:35(UTC)
Rank: Super forum user
descarte8

If someone wants to check my maths?

Lets assume

  • 5 excavators working in the area
  • Each generates 1 litre of emmissions per second
  • The composition of exhuast gas is 100,000ppm CO2 aka 10% (Note to answer the above question CO is a product of incomplete combustion which may be generated when the engine is "cold" but should be minimal when engine is running well (also less likely for diesel than petrol circa 0.05% / 500ppm))
  • The space is 30 meters deep and 50 meters long and 20 meters wide
  • The operation runs continuously for 8 hours a day
  • No mixing of the air inside the quary with outside (though you could get stratification within the 20 meter zone - if indoors maybe)

5litres (5x sources) of gas a second (0.5l CO2 (2.5ml CO)) = 14,400 litres in 8 hours (CO2) (72 litres CO)

Total volume of space/quarry = 30,000,000 litres

Concentration inside: 0.0069% CO2 aka 69ppm 0.00024% CO aka 2.4ppm

You can adjust the volume of the space, the gas rate production, and if you like the concentrations of CO / CO2 based on whether petrol or diesel( I have assumed diesel).  If you feel that there is so little movement that these gases could settle out you add in an air mover or 2? 

Or you could just hire a simple CO/Co2 meter for a week and take some measurements during the day and see how the concentrations changes over the working day - if at all

Edited by user 09 April 2018 12:22:16(UTC)  | Reason: to make bulleted list clearer

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