Section 4 Refrigerant charge limits, machinery room, and storage arrangements
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Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Naval Ships, January 2023 - Volume 2 Machinery and Engineering Systems - Part 11 Support Systems - Chapter 4 Refrigeration System Arrangements - Section 4 Refrigerant charge limits, machinery room, and storage arrangements

Section 4 Refrigerant charge limits, machinery room, and storage arrangements

Parent topic: Chapter 4 Refrigeration System Arrangements

4.1 Refrigerant classification

4.1.1 The design of the system and safety arrangements are to be implemented based on the class of refrigerant selected for use in the system. The refrigerant classification scheme, ISO 817 Refrigerants — Designation and safety classification, is to be considered regarding the flammability and toxicity class of the refrigerant. Flammable (Class 2L, 2, and 3) and toxic (Class B) refrigerants are not to be used in systems designed for non-flammable, non-toxic refrigerants.

4.1.2 The ‘practical limit’ of a refrigerant represents the highest acceptable concentration level of refrigerant in an occupied space which will not result in any impairment of crew (i.e. acute effects) or create a risk of ignition of the refrigerant. Values for the practical limit for different refrigerants are listed in ISO 5149-1 Refrigerating systems and heat pumps — Safety and environmental requirements.

4.2 Refrigerating machinery in accommodation spaces

4.2.1  In accommodation spaces the amount of refrigerant charge is to be restricted to the practical limit.

4.2.2 Accommodation spaces containing refrigerating machinery are to be provided with natural or mechanical ventilation and suitable clearance for ventilation is to be retained around the refrigerating machinery.

4.3 Refrigerating machinery in machinery spaces

4.3.1 Machinery spaces containing refrigerating machinery with an aggregate charge greater than the practical limit for the space are to be provided with refrigerant leak detection monitoring and alarm in accordance with Vol 2, Pt 11, Ch 4, 5.2 Refrigerant leak detection systems.

4.3.2 The maximum charge allowed in machinery spaces is limited as described in Vol 2, Pt 11, Ch 4, 4.4 Charge limits due to flammability and Vol 2, Pt 11, Ch 4, 4.5 Charge limits due to toxicity. Refrigeration machinery and storage vessels exceeding the maximum charge are to be located in a normally unmanned gastight ‘refrigeration machinery space’ in accordance with Vol 2, Pt 11, Ch 4, 4.6 Refrigeration machinery space.

4.4 Charge limits due to flammability

4.4.1 There is no restriction due to flammability on the charge size of flammability Class 1 refrigerants.

4.4.2 Machinery using flammability Class 2L, 2 and 3 refrigerants may be installed in machinery spaces providing the following controls are complied with:

  • The total mass of refrigerant in the space is limited to the values listed in Table 4.4.1 Refrigerant charge limits .
  • A mechanical ventilation system capable of 30 air changes per hour which is separate from ventilation systems serving other compartments is provided. The ventilation system is to be arranged to ensure a good flow of air around the refrigerating machinery. A lower flow may be used in normal operation provided the system can increase the flow in the event of a leak being detected, but is not to be below a minimum of ten air changes per hour.
  • The space shall be provided with fire protection equivalent to a category A machinery space.

4.4.3 If the refrigerant has the potential to produce toxic or corrosive products from combustion, these are to be considered in the fire-fighting design and appropriate warning signage provided adjacent to the machinery.

4.5 Charge limits due to toxicity

4.5.1 There is no restriction due to toxicity on the charge size of toxicity class A refrigerants.

4.5.2 Refrigeration machinery and storage vessels containing toxicity class B refrigerants may be installed in machinery spaces providing the total mass of refrigerant is limited to the values listed in Table 4.4.1 Refrigerant charge limits .

Table 4.4.1 Refrigerant charge limits

Refrigerant Properties Maximum allowable total refrigerant charge
Toxicity Flammability Machinery spaces Accommodation spaces
A 1 No charge restriction PL x V
2L 20% x LFL x V
2
3
B 1 ≤10 kg
2L 20% x LFL x V

but no greater than 10 kg
2
3

LFL = Lower flammability limit (kg/m3)

PL = Practical limit (kg/m3)

V = volume of compartment (m3) (see Note 1)

Note 1. Permeability of a compartment does not need to be considered for the calculation (permeability =1) however, large enclosed volumes such as gas turbine acoustic enclosures should be deducted from the total compartment volume.

4.6 Refrigeration machinery space

4.6.1 A refrigeration machinery space is to be a normally unattended, gastight space.

4.6.2 The compartment access door is to open outwards and is to be fitted with an easily operated opening mechanism to facilitate rapid escape in an emergency.

4.6.3 Where the refrigerating machinery space contains refrigerant of toxicity Class B the space is to be fitted with the following features:

  • Independent mechanical exhaust ventilation, ensuring at least ten air changes per hour in empty space.
  • Natural or mechanical supply ventilation independent of the ventilation of other spaces.
  • The ventilation system shall ensure under-pressure inside the refrigerating machinery space.
  • Clear signage indicating the potential hazard and warning not to enter when a leak has been detected.
  • Where the charge is greater than 50 kg, emergency body shower and eye wash facilities shall be installed locally outside the compartment.

4.6.4 Where the refrigerating machinery space contains refrigerant of flammability Class 2L, 2 or 3 the space is to be fitted with the following features:

  • A non-sparking mechanical exhaust ventilation system, with a capacity of at least 30 air changes per hour, which is arranged to avoid areas where gas may accumulate taking into account the density of the vapour and potential ignition sources. The ventilation system shall be separated from those serving other spaces.
  • All machinery and electrical equipment within the space is to be of a type suitable for a zone 2 hazardous area in accordance with Vol 2, Pt 9, Ch 5, 4 Electrical equipment for use in explosive gas atmospheres or in the presence of combustible dusts.
  • The leak detection is to be set to alarm at gas concentrations above 30 per cent lower flammable limit (LFL).
  • All spaces containing these refrigerants, including exhaust vents, are to be indicated on a hazardous area plan as described in Vol 2, Pt 9, Ch 1, 1 General requirements.

4.6.5 In addition to the main ventilation system required by Vol 2, Pt 11, Ch 4, 4.6 Refrigeration machinery space 4.6.3 and Vol 2, Pt 11, Ch 4, 4.6 Refrigeration machinery space 4.6.4, each refrigerating machinery space shall be fitted with an independent emergency exhaust ventilation system ensuring:

  • 30 air changes per hour – in the case of refrigerating machinery operating on Group 2l, 2 and 3 refrigerants.
  • 20 air changes per hour – in the case of refrigerating machinery operating on Group I refrigerants.

4.6.6 If the refrigerant has the potential to produce toxic or corrosive products from combustion these are to be considered in the fire-fighting design and appropriate warning signs provided at the entrance to the space.

4.6.7 The ventilation design is to consider the density of the refrigerant and draw from the appropriate location to ensure good air distribution and effective exhaust from the compartment.

4.6.8 The refrigerating machinery space shall have two means of escape arranged as far apart as practicable. Spaces with automated unattended refrigerating machinery, operating on Group A1 and B1 refrigerants, need not be provided with a second means of escape.

4.6.9 The starting and stopping arrangements for the ventilation shall be arranged both inside the refrigerating machinery space and outside, in the vicinity of the exit.

4.6.10 Drain pipes from the refrigerated machinery space are to be fitted with liquid sealed traps. Non-return valves are to be fitted in drain pipes from spaces located on the tank tops.

4.7 Refrigerant storage compartments

4.7.1 Portable cylinders containing reserve supplies of refrigerant are to be stored in the same compartment as the refrigeration machinery and included within the charge limit, or in a well-ventilated compartment reserved solely for this purpose.

4.7.2 Compartments for storage of toxic (Class B) or flammable (Class 2L, 2 or 3) refrigerants are to include the following features:

  • A mechanical ventilation system providing ten air changes per hour.
  • At least one door opening outwards giving direct access to open deck.
  • Clear signage indicating the potential hazard and warning not to enter when a leak has been detected.
  • Liquid sealed traps fitted to drain pipes. Non-return valves are to be fitted in drain pipes from spaces located on the tank tops.

4.7.3 In addition, all machinery and electrical equipment within compartments for storage of flammable (Class 2L, 2 or 3) refrigerants is to be of a type suitable for a zone 2 hazardous area in accordance with Vol 2, Pt 9, Ch 5, 4 Electrical equipment for use in explosive gas atmospheres or in the presence of combustible dusts.

4.7.4 Bulk storage tanks holding more than 150 kg of replacement carbon dioxide (class A1) are to be located in a dedicated compartment. The compartment is to be provided with the following features:

  • A mechanical ventilation system providing ten air changes per hour.
  • Ventilation system exhaust ducting positioned to remove air from the base of the compartment.
  • A gastight access door opening outward.

4.7.5 The compartment is to be provided with a refrigerant detection system in accordance with Vol 2, Pt 11, Ch 4, 5.2 Refrigerant leak detection systems.

4.7.6 Storage cylinders are to be of an approved type, and are to be filled to a level suitable for an ambient temperature of + 55°C.

4.7.7 The compartment is to be provided with racks to facilitate secure stowage of the cylinders.

4.7.8 The Naval Administration may require protection of flammable gasses from military attack.

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