Ammonia Refrigeration and Tight-Fitting Doors

In the recent OSHRC decision where the ALJ decided that “tight-fitting” doors for an engine room/machinery room doors were not a PSM requirement since “doors” were not part of the covered process. What is confusing is that the company successfully convinced the ALJ that ASHRAE 15 was not their chosen RAGAGEP (even though they stated it was in their PSI) and that the State’s Revised IMC was the required RAGAGEP. OSHA had, correctly, referenced ASHRAE 15 in both of these citations. So if we throw out ASHARE 15 and use the IMC to understand the importance of “tight-fitting doors” we see the following…

This section would apply to refrigerated spaces that contain refrigeration equipment, but not an engine room. We can see that engine rooms/machinery rooms are exempt from these requirements when ALL 7 items are present:
(emphasis by me)

1104.2.2 Industrial occupancies and refrigerated rooms.

This section applies only to industrial occupancies and refrigerated rooms for manufacturing, food and beverage preparation, meat cutting, other processes, and storage. Machinery rooms are not required where all of the following conditions are met:

1. The space containing the machinery is separated from other occupancies by tight construction with tight-fitting doors.
2. Access is restricted to authorized personnel.
3. The floor area per occupant is not less than 100 square feet (9.3 m2) where machinery is located on floor levels with exits more than 6.6 feet (2012 mm) above the ground. Where provided with egress directly to the out-doors or into approved building exits, the minimum floor area shall not apply.
4. Refrigerant detectors are installed as required for machinery rooms in accordance with Section 1105.3.
5. Surfaces having temperatures exceeding 800F (427C) and open flames are not present where any Group A2, B2, A3 or B3 refrigerant is used (see Section 1104.3.4).
6. All electrical equipment and appliances conform to Class 1, Division 2, hazardous location classification requirements of NFPA 70 where the quantity of any Group A2, B2, A3 or B3 refrigerant, other than ammonia, in a single independent circuit would exceed 25 percent of the lower flammability limit (LFL) upon release to the space.
7. All refrigerant-containing parts in systems exceeding 100 horsepower (hp) (74.6 kW) drive power, except evaporators used for refrigeration or dehumidification; condensers used for heating; control and pressure relief valves for either; and connecting piping, shall be located either outdoors or in a machinery room.

This section contains provisions for industrialized food processing plants, manufacturing plants and refrigerated storage. Refrigeration systems in these spaces need not be contained in a machinery room as long as all of the seven items of this section are met. “Industrial occupancy” is defined in Section 1103.2 and does not necessarily coincide with the description in Section 306 of the IBC for a Group F occupancy. Because these occupancies are restricted to employees who are familiar with their surroundings and contain low occupant loads, the hazard is perceived to be reduced. Item 3 specifically limits the occupant density when occupants would have to travel down open interior stairs to leave the building. This restriction does not apply if the required exit doors from the space lead directly to exterior stairs or to stairs enclosed with fire-resistance-rated construction and protected openings in accordance with the IBC for interior exit stairs. The “lower flammability limit” mentioned in Item 6 is defined in Chapter 2 of the code as “the minimum concentration of refrigerant that is capable of propagating a flame through a homogeneous mixture of refrigerant and air” [see definition of “Lower flammability limit (LFL)”]. If a refrigerant were released into the air, thus mixing with the air (to create a homogeneous mixture), a certain concentration would eventually be reached that would make the air/refrigerant mixture flammable/explosive. The lowest concentration at which this could occur is the LFL. Item 6 limits the amount in a single circuit to 25 percent of the amount needed to attain the LFL, unless all electrical equipment and appliances in the space conform to the Class 1, Division 2 hazardous location requirements found in NFPA 70. The flammability classification of the refrigerants used can be obtained from the manufacturer or the MSDS for the refrigerant. See also the definition of “Flammability classification” in Chapter 2.

So why does the IMC/IBC, ASHRAE, IIAR all require “tight-fitting” doors where ammonia refrigeration equipment is located?

They are intended to act like a “secondary containment” should a release occur inside the engine room/machinery room, or as stated above in the IMC, inside a refrigerated room used for manufacturing, food and beverage preparation, meat cutting, other processes and storage. Many may not release the pressure rise inside a space where liquid ammonia is released. With a VP of nearly 7,000 mm Hg and a BP of -28F, the liquid flashes to gas quickly and expands 680 to 1. Without tight-fitting, and I need to add “latched closed” doors the ammonia gas will spread anywhere and everywhere it can. The tight-fitting doors are intended to contain the ammonia in the space that is designed to handle it. Poorly, or loose fitting doors, will be pushed open by the expanded gas and allow ammonia to find its way into occupied spaces or spaces that are not designed to see ammonia gas.