Confined spaces are places where the accident rate is particularly significant in the field of industrial safety.
Accidents in these enclosures are probably the second leading cause of death in the industrial sector, and NIOSH estimates that (The National Institute of Occupational Safety Health) two-thirds of the deaths causedby the existence of hazardous atmospheres.
Not only that, but almost 75% of the time, such atmospheres already existed before performing jobs in confined spaces.
But what is a confined enclosure?
It is a space in which the entrance and exit openings are limited, and where natural ventilation is unfavorable.
This makes confined enclosures a place prone to the accumulation of toxic or flammable contaminants.
They are also prone to an oxygen-deficient atmosphere and are not designed for continued occupancy by the operator.
What types of confined spaces are there?
There are many types of confined spaces, but among them we can find:
- Reactors
- Storage tanks
- Underground transformer rooms
- Tunnels
- Sewers
- Boat holds
- Transport tanks
The reasons why these confined spaces are accessed are:
- Construction of the enclosure itself
- Cleaning
- Painting
- Reparation
- Inspection
What risks exist in a confined space?
Among the most common risks are:
Oxygen shortage
We have already mentioned that one of the characteristics of a confined space is the existence of an oxygen-deficient atmosphere.
This is due to the very fact of consuming the limited oxygen that there is, and that is not renewed at a sufficient rate, due to the lack of good ventilation.
It can also be due to the displacement of oxygen by other gases.
In general, the optimal oxygen concentration should be 21%, from lower percentages the consequences can be the following:
- 20.5%: Minimum concentration to enter without equipment with air supply
- 18%: Atmosphere deficient in oxygen, resulting in problems of muscle coordination and acceleration of respiratory rhythm
- 17%: Risk of loss of consciousness without precursor sign.
- 12-16%: Vertigo, headaches, dyspnea, high risk of unconsciousness
- 6-10%: Nausea, loss of consciousness followed by death in 6-8minutes
This is generated, among many other causes, by:
- Detachment of carbon dioxide (CO2) in aerobic organic fermentations in sewers, storage tanks, wells, tunnels, wine vats and vats, cereal silos, among others.
- Work in welding, heating, or cutting.
- Oxidation of the inner metal surface of tanks
- Detachment of methane (CH4) product of anaerobic organic fermentations in septic tanks, sewer networks, wastewater treatment digesters, etc.
Explosive atmospheres
It is very easy for ATEX environments to be generated in confined spaces, due to that lack of sufficient natural ventilation, and for some of the following reasons:
- Detachment of flammable products absorbed on the inner surface of containers
- Solvent vapors in painting work and flammable substance vapours in tank cleaning operations
- Loading, unloading, and transporting combustible dusts (cereals, rubber, feed...)
- Even enrich the confined space with oxygen to "improve" breathable air quality
Accumulation of toxic substances
This can lead to intoxication of the operator which, in addition, is of acute grade, because the concentration that is produced of these substances is very high.
These toxic substances can occur well, because the conditions already existed previously, or because of the work carried out by the operator.
To these must be added the irritating and corrosive atmospheres due to the existence of chlorine, hydrochloric acid, or ammonia.
Dangerous reactions with generation of toxic gases:
- Release of hydrogen sulfide gas through the reaction of sulfides with acids
- General network of drains of tanning industries
- Cleaning of tanks or tanks containing sulphurous residues with acidic products
- Release of nitrous oxides by reaction of nitrites with organic substances
- Presence of carbon monoxide
- Enclosures where incomplete combustion processes have occurred: extraction of liquids with pumps with internal combustion engine
- Toxic substances generated during work
- Welding and oxyfuel work on stainless steel parts containing cadmium
- Uses of organic solvents in degreasing and cleaning
- Application of coatings inside tanks
- Existence of toxic substances from the production process itself or waste
Sources:
NTP 223: Work in Confined Spaces
Image: "Confined Space Warning 01" by Joe Mabel licensed under CC BY-SA 3.0
