Source: Ontario Ministry of Labour
Equipment for recovering solvents can be found wherever solvents are used; for example, in body shops. This data sheet focuses on solvents that have a flash point of 149C (300F) or less and that are recovered by distillation after being heated to or above their boiling points. (Refer to Factory Mutual Loss Prevention Data 7-2, “Waste Solvent Recovery”.)
Vapours produced by flammable solvents or solvents heated to their boiling point may form explosive mixtures with air. If such a mixture comes into contact with a source of ignition, an explosion or fire will occur. Potential ignition sources in a solvent recovery operation include arcs or sparks from electrical installations on or near the equipment. Other nearby ignition sources must also be taken into account, as well as the fact that many solvent vapours will accumulate and spread out near the floor because they are heavier than air.
It should be noted that some solvent recovery equipment that is approved only for non-flammable solvents is being improperly used to recycle flammable solvents or solvents with a flash point. This can also result in explosions or fires.
“Flash point” means the minimum temperature at which a liquid within a container will give off enough vapours in sufficient concentration to form an ignitable mixture with air near the surface of the liquid.
“Flammable liquid” means a liquid with a flash point below 37.8C (100F) and a vapour pressure below 275 kPa absolute (40 psig) at 37.8C (100F). These are the standard legal criteria for classification as a flammable liquid (see National Fire Code, section 1.2). However, please note that many substances that do not meet these criteria will burn if the temperature is high enough.
Batch distillation is the most common type of solvent recovery operation. A batch of contaminated solvent mixture is heated to its boiling point and the resulting vapour is condensed, either in air or in a water-cooled condenser.
After the batch has been distilled, the contaminants remain in the boiler and are removed.
The container for the dirty solvent may be either fixed or removable. A plastic liner, suitable for high temperatures, may be used with a fixed container to facilitate clean-up. These liners are normally found in the smaller sizes of equipment.
Most recovery equipment operates at or near atmospheric pressure, but some equipment has a vacuum system to lower the pressure in the dirty solvent container. Lower pressure results in lower solvent boiling points and so allows a lower operating temperature.
Solvent recovery equipment with a capacity of 23 litres (5 gallons) or more must be located:
- in a detached building used for no other purpose, or
- in an attached building or in a room with at least one exterior wall, separated from the rest of the building with partitions having a fire-resistance rating of at least one hour and self-closing doors that are hinged to swing outwards on their vertical axes.
Explosion venting to the outdoors must be provided for the room or building to prevent critical structural and mechanical damage from an internal explosion. The explosion venting must conform with good engineering practice, as described in NFPA (National Fire Protection Association) 68, “Venting of Deflagrations” or Factory Mutual 1-44, “Damage Limiting Construction”. Pressure-resisting walls and roofs should be designed to withstand explosion pressures of at least five times the relieving pressure of the explosion vents without collapse.
Means of containing spills around the solvent recovery equipment and containers should be provided.
A room containing solvent recovery equipment should have: a drain connected to a holding tank; liquid-tight seals between the interior walls and the floor; and a liquid-tight ramped sill at any door opening that is not in an exterior wall.
Solvent Storage and Handling
Containers used for dispensing flammable liquids must be bonded and grounded during dispensing operations.
Removable solvent containers containing solvent should have their lids sealed and secured onto them at all times except when they are being filled or emptied.
Refer to sections 5 and 6 of Engineering Data Sheet 4-01, “Storage and Dispensing of Flammable Liquids”, for further information.
Effective local exhaust ventilation must be provided across all portions of the affected floor and room space to prevent the accumulation of flammable solvent vapours. This ventilation must be in operation:
- during the distillation process, including the period when the solvents are cooling, and
- whenever containers are not sealed.
- For solvent recovery equipment with a capacity of less than 23 litres (five gallons), effective local exhaust is recommended. This could be accomplished by using an overhead hood to capture heated vapours and an enclosure surrounding the sides and back with provision for exhaust near the floor area. The ventilation fan should be of non-sparking construction.
For recovery equipment with a capacity of 23 litres (five gallons) or more, effective continuous mechanical ventilation must be provided at a minimum rate of 18 cubic metres per hour per square metre (one cubic foot per minute per square foot) of the floor area of the room or building.
Worker exposure to solvent vapours must not exceed the levels permitted under the Biological or Chemical Agents Regulation (O.Reg. 833/90) in an area where solvent recovery equipment is located.
For solvent recovery equipment with a capacity of less than 23 litres (5 gallons):
- electrical equipment must be suitable for use in Class I, Division 1 hazardous locations when it is within 1.5 metres (five feet) in all directions from the edge of the solvent recovery equipment;
- electrical equipment must be suitable for use in Class I, Division 2 hazardous locations when it is within 0.9 metres (three feet) beyond Division 1 in all directions;
- electrical equipment must be suitable for use in Class I, Division 2 hazardous locations when it is up to 0.9 metres (three feet) above floor or grade level and within six metres (20 feet) horizontally beyond Division 1; and
receiving containers must be considered as part of the equipment unless located outdoors.
Solvent recovery equipment with a capacity of 23 litres (five gallons) or more must be located in a room or in a separate building (section 4). The electrical equipment in the room or building must be suitable for use in Class I, Division 1 hazardous locations.
For solvent recovery equipment vents, including safety valves piped to the outdoors, and for receiving container vents that extend to the outdoors:
- electrical equipment must be suitable for use in Class I, Division 1 hazardous locations when it is within 0.9 metres (three feet) in all directions around the open end of the vent, and
- electrical equipment must be suitable for use in Class I, Division 2 hazardous locations when it is within 0.6 metres (two feet) beyond Division 1 in all directions.
For container fill openings:
- electrical equipment must be suitable for use in Class I, Division 1 hazardous locations when it is within 0.9 metres (three feet) in all directions from the fill opening;
- electrical equipment must be suitable for use in Class I, Division 2 hazardous locations when it is within 0.6 metres (two feet) beyond Division 1 in all directions; and
- electrical equipment must be suitable for use in Class I, Division 2 hazardous locations when it is up to 0.45 metres (1.5 feet) above floor or grade level and within 2.1 metres (seven feet) horizontally beyond Division 1.
All sources of static electricity must be eliminated by proper grounding and bonding of solvent recovery equipment and containers.
Other Ignition Sources
In addition to the requirements set out in section 8, there must be no other sources of ignition in a room or an area where recovery equipment is located. Possible sources of ignition, besides electrical sparks and static electricity, include: open flames, hot surfaces, ovens, furnaces, heating equipment, smoking, cutting and welding, frictional heat or sparks, radiant heat, grinding and wood stoves.
The safety features of solvent recovery equipment must be determined before it is installed. Safety features include: properly classified electrical wiring; overheating protection; ignition source elimination; a pressure control/relief valve; and interlocks to prevent opening the still while the contents are hot or being heated.
The recovery equipment must be maintained and inspected as recommended by the manufacturer.
The safety valve on a solvent container must be piped to the outdoors in such a way that no solvent will re-enter the building or enter any adjacent premises. The venting system should meet the requirements of the Environmental Approvals and Planning Branch of the Ministry of Environment and Energy.
Regulations and Codes
Biological or Chemical Agents Regulation, O.Reg. 830/90
Regulations for Industrial Establishments, R.R.O. 851/90 (sections 22 and 63)
National Fire Code of Canada, 1995
Ontario Electrical Safety Code, 21st ed.
National Fire Protection Association, NFPA 30, “Flammable and Combustible Liquids Code”
National Fire Protection Association, NFPA 68, “Venting of Deflagrations”
Factory Mutual Loss Prevention Data 1-44, “Damage Limiting Construction”
Factory Mutual Loss Prevention Data 7-2, “Waste Solvent Recovery”
Ministry of Labour Engineering Data Sheet
#4-01 “Storage and Dispensing of Flammable Liquids”