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53.2 Safety Features
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Operation of an automatic crossover valve shall cause all compressors on the affected system to immediately stop in accordance with the following:
- Dedicated pressure-sensing devices located immediately adjacent to crossover valves shall be permitted as a means for determining operation of a valve.
- To ensure that the automatic crossover valve system provides a redundant means of stopping compressors in an overpressure condition, high pressure cutout sensors associated with compressors shall not be used as a basis for determining operation of a crossover valve.
Activation of the overpressure sensing device shall cause all compressors on the affected system to immediately stop.
Unless the AHJ determines, upon review of an engineering analysis prepared at the expense of the owner, that a significant fire, health, or environmental hazard would not result from an atmospheric release, refrigeration systems that are designed to discharge refrigerant vapor to the atmosphere shall be provided with an approved treatment, flaring, or diffusion system where required by 220.127.116.11.1 through 18.104.22.168.3.
Systems containing flammable refrigerants shall discharge vapor to the atmosphere in accordance with the following:
- For refrigerants having a density equal to or greater than the density of air, discharge shall be through an approved treatment system in accordance with or flaring system in accordance with 22.214.171.124.
- For refrigerants having a density less than the density of air, discharge to the atmosphere shall be permitted, provided that the point of discharge is located outside of the structure at not less than 15 ft (4.6 m) above the adjoining grade level and not less than 20 ft (6.1 m) from any window, ventilation opening, or exit.
Systems containing ammonia refrigerant shall discharge vapor to the atmosphere through a treatment system in accordance with 126.96.36.199, through a flaring system in accordance with 188.8.131.52, through an approved ammonia diffusion system in accordance with 184.108.40.206, or by other approved means except as follows:
- Discharge through a treatment, flaring, or diffusion system shall not be required for ammonia-water absorption unit systems installed outdoors serving a dwelling unit, provided that the discharge is shielded and dispersed.
- Discharge through a treatment, flaring, or diffusion system shall not be required for ammonia-water absorption unit systems containing less than 22 lb (10 kg) of ammonia and for which the ammonia circuit is located entirely outdoors.
Flaring systems for incineration of flammable, toxic, or highly toxic refrigerants or ammonia shall be designed to incinerate the entire discharge.
The products of refrigerant incineration shall not pose health or environmental hazards.
Incineration shall be automatic upon initiation of discharge, shall be designed to prevent blowback, and shall not expose structures or materials to threat of fire.
Standby fuel, such as LP-Gas, and standby power shall have the capacity to operate for one and one half the required time for complete incineration of refrigerant in the system.
The water used shall be prevented from freezing without the use of salt or chemicals by burial of the discharge pipe below frost depth or other approved means.
The tank shall be substantially constructed of not less than 1/8 in. (2.51 mm) (10 gauge) steel.
The horizontal dimensions of the tank shall be equal to or less than one half of the height.
The tank shall have a hinged cover or, if of the enclosed type, shall have a vent hole at the top.
The refrigerant vapor detector shall activate approved visual and audible alarm signaling devices at one of the following refrigerant thresholds:
- At a value not greater than the corresponding TLV-TWA (or toxicity measure consistent therewith); not to exceed 25 percent of the lower flammable limit (LFL)
- For ammonia, at a concentration not exceeding 25 parts per million
Audible and visual alarm signaling devices shall be located inside the refrigeration machinery room and outside the room at each entrance into the room.
Where the quantity of a Group A2, B2, A3, or B3 refrigerant, other than ammonia, in an independent circuit would exceed 25 percent of the LFL if released to the surrounding room, either of the following shall apply:
Open flames or devices having an exposed surface temperature exceeding 800°F (427°C) shall be prohibited in refrigeration machinery rooms except as follows:
- Momentary temperature excursions such as electrical contacts in Group A1 and B1 systems shall be permitted.
- Open flames or devices having an exposed surface temperature exceeding 800°F (427°C) shall be permitted in refrigeration machinery rooms used exclusively for direct-fired absorption equipment.
- Existing nonconforming installations shall be permitted where approved by the AHJ, where the combustion system is interlocked with the refrigerant detection system to shut off at the permissible exposure limit (PEL).
- Direct-vented combustion equipment shall be permitted in accordance with the mechanical code.
For systems using a refrigerant other than ammonia, purge fans shall also respond automatically to the refrigerant concentration detection system set to activate the ventilation system at the threshold levels set forth in 220.127.116.11.1. For systems using ammonia, purge fans shall also respond automatically to the refrigerant concentration detection system set to activate the ventilation system at an ammonia concentration not exceeding 150 parts per million.
Mechanical ventilation systems serving refrigeration rooms shall have switches to control the power to each fan.
The switches shall be key-operated or within a locked glass-covered or tamper-resistant enclosure at an approved location adjacent to and outside of the principal entrance to the refrigeration machinery room.
Switches controlling fans providing continuous ventilation shall be of the two-position, on/off type.
Switches controlling fans providing intermittent or emergency ventilation shall be of the three-position, automatic on/off type.
Switches shall be labeled identifying both the function and the specific fan being controlled.
Two colored and labeled indicator lamps responding to the differential pressure created by airflow shall be provided for each switch.
One lamp shall indicate flow, and the other shall indicate no flow.
Exhaust from mechanical ventilation systems in refrigeration rooms shall be discharged 20 ft (6.1 m) or more from a property line or openings into buildings.
Discharges capable of exceeding 25 percent of the LFL or 50 percent of the immediately dangerous to life and health (IDLH) value shall be equipped with approved treatment systems to reduce the discharge concentrations to these values or lower, except as provided in 18.104.22.168.13.1 and 22.214.171.124.13.2. (Also see 126.96.36.199.)
Refrigeration machinery rooms used exclusively for direct-fired absorption equipment shall be permitted not to be classified as a hazardous location for electrical equipment in accordance with NFPA 70.
Electrical equipment and electrical installations in refrigeration machinery rooms shall comply with Section 11.1.
A clearly identified switch of the break-glass type or with an approved tamper-resistant cover shall provide off-only control of refrigerant compressors, refrigerant pumps, and normally closed, automatic refrigerant valves located in the machinery room. In addition, this equipment shall be automatically shut off whenever the refrigerant vapor concentration in the machinery room exceeds the vapor detector's upper detection limit or 25 percent of the LFL, whichever is lower.
In machinery rooms where only nonflammable refrigerants are used, only compressors shall be required to be stopped by vapor detection or the cut-off switch. (Also see 188.8.131.52.4.)
Refrigeration units or systems shall be provided with approved hazard identification signs in accordance with NFPA 704, emergency operational signs, charts, and labels in accordance with the mechanical code, and the following:
- Name and address of the manufacturer or installer
- Type and total number of pounds of refrigerant contained in the system
- Field test pressure applied
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