Confined spaces can visually look completely safe but as we know, often they are not. Historically, atmospheric hazards have been the leading cause of deaths in confined spaces. In order to assess atmospheric hazards, both visual inspections and atmospheric testing of confined spaces must be done. There is often more than meets the eye!
When you look at a confined space, you must ASSUME that it could have a hazardous atmosphere until you verify that it is safe with a properly selected and calibrated gas monitor. But while it may be quite clear that there is a need to test a tank that contained chemicals previously, it may NOT be so clear that you need to test a space that looks fairly innocuous such as a valve or meter pit that never contained a chemical. Yet these spaces have the potential for hazardous atmospheres from numerous sources. Contaminants can enter confined spaces located below grade through walls and floors from leaking underground gas and fuel lines even a mile away. Decaying vegetation and debris in vaults and pits can create flammable methane and toxic hydrogen sulfide.
And what if the tank only contained water previously? How bad could it be? Water tanks may be rusty. The rusting process uses up oxygen and that may lead to an oxygen deficient environment. What about a brand new concrete vault? Concrete can use up oxygen as it cures and can in some situations may create an oxygen deficient environment. So even a brand new concrete vault may contain a hazardous environment. Is nothing safe??
You may now be convinced of the importance of testing the atmosphere regardless of how benign the confined space. But wait, there is more….
Testing the atmosphere is only one step in assessing atmospheric hazards. Visual inspections are important because small pools of liquids or debris lying stagnant in the bottom of a tank may not necessarily be vaporizing at a level to register on a gas monitor. However after the space is opened and heat, ventilation or a worker walking around in or cleaning up the liquid changes the atmosphere, this liquid may to begin to vaporize and create a hazardous atmosphere. It does not take a lot of liquid that is vaporizing in the bottom of a tank to reach dangerous atmospheric levels. Decaying debris in the bottom of a confined space may contain pockets of gases that are released when workers stir up the debris when inside the tank to perform work or cleaning. So the gas monitor reading is critical but may provide a false sense of security unless visual inspection is also part of the assessment.
NFPA is in the process of developing a Best Practices document for confined space entry. If you have ideas for what should be included in this document or would like to be involved in document development please let us know! Task groups to develop draft chapters of the document are now being formed. If you have an interest or special expertise in a particular area and would like to work with a task group let us know how to contact you!