I have written several articles lately explaining the limitations of storing flammables and toxics. A couple of these articles referenced the International Fire Code (IFC) which is my favorite safety code for hazardous materials. OSHA’s 1910.106 is from the 1969 NFPA 30 and has not been sustainably updated since; whereas the IFC gets updated every three (3) years. In the IFC the limitations for storage and handling are based on the process/system being “open” or “closed”, and of course a closed system is permitted to handle much more of the HAZMAT. So what is the difference?
The IFC defines a “CLOSED SYSTEM” as…
The use of a solid or liquid hazardous material involving a closed vessel or system that remains closed during normal operations where vapors emitted by the product are not liberated outside of the vessel or system and the product is not exposed to the atmosphere during normal operations; and all uses of compressed gases. Examples of closed systems for solids and liquids include product conveyed through a piping system into a closed vessel, system or piece of equipment.
The difference between a closed system and an open system is whether the hazardous material involved in the process is exposed to the atmosphere. A closed system is inherently less hazardous than an open system due to the fact that vapors, dust, or similar materials are not normally released from closed systems. Because closed systems are less hazardous than open systems, credit is typically given to increase the maximum allowable quantities (MAQ) when systems are considered closed. NOTE: the IFC states that materials in closed or open systems are assumed to be “in use” as opposed to “in storage.” Gases are always assumed to be in closed systems since they would be immediately dispersed in an open system if exposed to the atmosphere without some means of containment (see the definition of “Open system”).
OPEN SYSTEM
The use of a solid or liquid hazardous material involving a vessel or system that is continuously open to the atmosphere during normal operations and where vapors are liberated or the product is exposed to the atmosphere during normal operations. Examples of open systems for solids and liquids include dispensing from or into open beakers or containers, dip tank and plating tank operations.
Generally, an open system is one that will normally be open to the atmosphere; for example, a dip tank or dispensing or mixing of hazardous materials. Open systems are inherently more hazardous than closed systems. When evaluating the MAQs of hazardous materials and the associated requirements, open systems are more heavily regulated.
For example:
Table 5003.1.1(3) specifies the Maximum Allowable Quantities (MAQs) of hazardous materials, liquids or chemicals allowed per outdoor control area before being subject to additional regulations contained in Chapters 51 and 53 through 67, and is subdivided based on whether the material is in storage or in use in a CLOSED or OPEN system. Within these subdivisions, the appropriate MAQ is listed in accordance with the physical state (solid, liquid or gas) of the material. A column for gas in open systems is NOT indicated because hazardous gaseous materials MUST NOT be allowed in a system that is continuously open to the atmosphere.
Table 5003.1.1(4), similar to Table 5003.1.1(3), specifies the Maximum Allowable Quantities (MAQs) of hazardous materials, liquids or chemicals allowed per outdoor control area before being subject to additional regulations contained in Chapters 51 and 53 through 67. It is also subdivided based on whether the material is in storage or in use in a closed or open system. Within these subdivisions, the appropriate MAQ is listed in accordance with the physical state (solid, liquid or gas) of the material.