Elimination of the need for entering confined spaces for vapour degreaser maintenance
Problem
In the cleaning of aircraft parts, a tri-chloroethane (1.1.1) solution was used. The ‘trico’ was heated by coils in the bottom of a degreasing tank until it reached 77°C when it formed a vapour. The vapour would rise in the tank until it came into contact with cold air ’blanket’ caused by cooling coils placed around the inside of the tank near its top. Parts to be cleaned were suspended in the vapour while this process continually repeated itself.
When a process was finished the heating coils would be switched off and the contaminated ‘trico’ would return to the sump. After many cleaning operations, a worker would enter the tank to clean and remove the sludge (a mixture of oil, dirt, grease and tri-chloroethane). Entry into this confined space was dangerous especially if the tank had not been thoroughly purged of trichloroethane vapour which can cause narcosis and death. Additionally, the potential for explosion or fire existed.
Solution
The new procedure allows the trichloroethane to be evaporated, condensed and collected in a separate holding facility. During the cleaning process and at its end, vapour is collected in a drain chute just below the degreaser’s cooling coils. The condensed vapour, which is free of contaminants, is stored in closed drums. The sump is no longer used.
The remaining sludge (now with a much smaller ‘trico’ ratio) in the tank is allowed to cool for half an hour. Once cooled the sludge is scooped out with an extended shovel / scoop that was specially made for the process and removes the need for tank entry. Once the sludge has been removed the stored, clean condensate is returned to the tank via a pump.
Hierarchy of Controls:
Engineering
Benefits
- The new procedure eliminates the need to work in a confined space.
- The cleaning procedure is carried out once every three weeks.
- It was estimated that $20,000 per annum is saved in solvent costs due to the method.
- A benefit to the environment must also be recognised as the dirty solvent is not now disposed of but is re-used through distillation.
- The risk of explosion or fire has been significantly reduced.