A process, in terms of Process Safety Management, is defined as:
“Any activity involving a regulated substance including any use, storage, manufacturing, handling or on-site movement of such substances, or any combination of these activities. For the purposes of this definition, any group of vessels that are interconnected, or separate vessels that are located such that a regulated substance could be involved in a potential release, shall be considered a single process”.
Here is a breakdown of the term…
Vessel means a reactor, tank, drum, barrel, cylinder, vat, kettle, boiler, pipe, hose, or other containers.
If you store a regulated substance in a single vessel in quantities above the threshold quantity, you are covered
- If you have interconnected tanks that hold more than a threshold quantity that can be involved in a single event, you are covered. The connections need NOT be permanent. If two vessels are connected occasionally, they are considered a single process for the purposes of determining whether a threshold quantity is present.
- If you have multiple unconnected tanks, cylinders, barrels, or other containers, including pipes, containing the same substance, you will have to determine whether
they need to be considered together.
SINGLE VESSEL
Many people covered by the CalARP regulations will have a single storage tank and fall into the first group. If one tank is the only place you have a regulated substance, you need not worry about the other possibilities for defining a process.
INTERCONNECTED VESSELS
In general, if you have two or more vessels containing a regulated substance that are connected through piping or hoses for the transfer of the regulated substance, you must consider the total quantity of a regulated substance in all the connected vessels and piping when determining if you have a threshold quantity in a process. If the vessels are connected for transfer of the substance using hoses that are sometimes disconnected, you still have to consider the contents of the vessels as one process, because if one vessel were to rupture while the hose was attached or the hose were to break during the transfer, both tanks could be affected. Therefore, you must count the quantities in both tanks and in any connecting piping or hoses. You cannot consider the presence of automatic shutoff valves or other devices that can limit flow, because these are assumed to fail for the purpose of determining the total quantity in a process.
Once you have determined that a process is covered (the quantity of a regulated substance exceeds its threshold), you must also consider equipment, piping, hoses, or other interconnections that do not carry or contain the regulated substance, but that are important for accidental release prevention. Equipment or connections which contain utility services, process cooling water, steam, electricity, or other non-regulated substances may be considered part of a process if such equipment could cause a regulated substance release or interfere with mitigating the consequences of an accidental release. Your prevention program for this process will need to cover such equipment. If, based on your analysis, it is determined that interconnected equipment or connections not containing the regulated substance cannot cause a regulated substance release or interfere with mitigation of the consequences of such a release, then such equipment or connections could safely be considered outside the limits or boundaries of the
covered process.
In some cases, such as in a large refinery or multi-unit chemical plant, determining the boundaries of a process for purposes of the RMP rule may be complicated. In the preamble to the June 20, 1996 rule (61 FR 31668), EPA clearly stated its intent to be consistent with OSHA’s interpretation of “process” as that term is used in OSHA’s PSM rule. Therefore, if your stationary source is subject to the PSM rule, the limits of your process(es) for purposes of OSHA PSM will be the limits of your process(es) for purposes of RMP (except in cases involving atmospheric storage tanks containing flammable regulated substances, which are exempt from PSM but not RMP). OSHA has issued several interpretation letters on the subject of interconnected units and facilities. OSHA has issued guidance for determining the limits of a process for four (4) general scenarios.
First, if a process unit containing a regulated substance above the threshold quantity (TQ) is interconnected (or proximate) to a process unit with the same regulated substance above or below the TQ, the process units are considered one covered process.
Second, if a process unit containing one regulated substance above TQ is interconnected (or proximate) to a process unit containing a second regulated substance above TQ, the process units are considered one covered process.
Third, if a process unit containing a regulated substance above TQ is interconnected (or proximate) to a process unit containing a non-regulated substance, the stationary source must apply the following criteria to determine if the process units are considered one covered process:
- if the unit with a non-regulated substance could cause a release in the interconnected or proximate unit it is considered one covered process
- if the unit with a non-regulated substance could interfere in the mitigation of a release in the interconnected or proximate unit it is considered one covered process
Fourth, if a process unit containing one regulated substance above TQ is interconnected (or proximate) to a process unit containing a second regulated substance below TQ, the stationary source must apply the following criteria to determine if the process units are considered one covered process:
- if the unit with the regulated substance below TQ could cause a release in the interconnected unit it is considered one covered process
- if the unit with a regulated substance below TQ could interfere in the mitigation of a release in the interconnected unit it is considered one covered process
Physical or administrative controls may NOT be used to segregate interconnected process units.
CO-LOCATION
The third possibility you must consider is whether you have more than a threshold quantity in separate vessels that are located so they could be involved in a single release. Such co-located vessels (interconnected or not) are part of a single process if there is a reasonable likelihood that they would be affected by the same event. If so, you must count the total quantity in all such vessels. This possibility will be particularly important if you store a regulated substance in cylinders or barrels or other containers in a warehouse or outside in a rack. In some cases, you may have two vessels or systems (e.g., refrigeration systems, acids baths) that are in the same building or room. For each of these cases, you should ask yourself:
- Would a release from one of the containers lead to a release from the other? For example, if a cylinder of propane were to rupture and burn, would the fire
spread to other propane cylinders? - Would an event external to the containers, such as a fire or explosion, have the potential to release the regulated substance from multiple containers? Co-located vessels (interconnected or not interconnected) are part of a single process if there is a reasonable probability that they would be affected by the same event.
For flammables, you should consider the distance between vessels. If a fire could spread from one vessel to the others, you must count all of them.
For toxics, a release from a single vessel will not normally lead to a release from others unless the vessel fails catastrophically and explodes, sending metal fragments into other vessels.
Co-located vessels containing toxic substances, however, may well be involved in a release caused by a fire or explosion that occurs from another source. In addition, a collapse of storage racks could lead to multiple vessels breaking open. If firewalls or barricades that will contain the blast waves from explosions of the substances separate the vessels, you will not need to count the separated vessels, but you would count any that are in the same room.
You should not dismiss the possibility of a fire spreading based on an assumption that your fire brigade will be able to prevent the spread. You should ask yourself whether the fire would spread to engulf all the vessels if the worst happens and the fire brigade is slow to arrive, the water supply fails or the local fire department decides it is safer to let the fire burn itself out. If vessels, taken together, have more than a threshold quantity, you should count them as a single process.