CRSC · California Referenced Standards Code
How does the code define primary/secondary protective barriers and useful beam?
Primary barriers stop the intended X‑ray beam (plus a required 1‑ft margin) and secondary barriers control leakage and scatter; operator booths and viewing windows must meet the same attenuation rules and final shielding values are set by the CRSC technical tables in Section 12‑31C‑101.
Last reviewed: July 6, 2026
What the code requires — 2-4 sentences
The California Referenced Standards Code defines a primary protective barrier, secondary protective barrier, stray radiation, and useful beam in § 3101C. In plain English: a primary protective barrier is the shield intended to stop the useful beam, while a secondary protective barrier attenuates stray radiation (leakage and scatter). These definitions and the cross-references to required shielding standards are established in § 3101C.
The single most important point: the code separates radiation the machine intentionally emits along its aimed path (the useful beam) — which must be stopped by primary protective barriers — from unwanted leakage or scatter (called stray radiation) which is controlled by secondary protective barriers (see § 3101C).
Requirements in detail
Key defined terms (first appearance bolded)
- Primary protective barrier — a barrier to attenuate the useful beam. § 3101C.
- Secondary protective barrier — a barrier to attenuate stray radiation. § 3101C.
- Stray radiation — radiation not serving any useful purpose; includes leakage and scattered radiation. § 3101C.
- Useful beam — radiation that passes through the window, aperture, cone or other collimating device of the tube housing. § 3101C.
How the definitions are applied (operational rules)
- Areas that can be struck by the useful beam (walls, floor, ceiling), plus a border of 1 foot (305 mm) around those struck areas, must be provided with primary protective barriers. § 3104C.1.
- Operator control stations must be behind a protective barrier that will intercept the useful beam and any radiation scattered only once (i.e., primary-level protection for control locations). § 3103C.1.
- Observation windows used at operator stations must provide radiation attenuation equal to the surrounding barrier — they are treated as part of the protective barrier. § 3103C.2.
- All radiation shielding barriers must meet the detailed attenuation requirements found in Section 12‑31C‑101, Chapter 12‑31C, Part 12 of the California Referenced Standards Code (CRSC) — compliance with those technical attenuation tables/calculations is required. § 3102C.
Decision-relevant dimensions / values
| Decision item | Value / threshold | Where to apply it | Code Reference |
|---|---|---|---|
| Border added to areas struck by useful beam | 1 foot (305 mm) | Add around every wall/floor/ceiling area that can be struck by the useful beam | § 3104C.1 |
| Operator station shielding performance | Must intercept the useful beam and single-scatter radiation | Control booth / protected booth / separate room for operator | § 3103C.1 |
| Observation window attenuation | Equal to surrounding barrier attenuation | Any viewing window into the patient/treatment area | § 3103C.2 |
| Source of technical attenuation requirements | Section 12-31C-101 (CRSC) — use those shielding tables/calculations | All radiation shielding barriers | § 3102C |
Note: the CRSC text in these retrieved excerpts sets the definitions and scope and points you to the specific CRSC attenuation standards (Section 12‑31C‑101) for the numerical shielding design; the attenuation tables / lead equivalencies themselves were not included in the retrieved snippets.
Exceptions & special cases
- Variances or exceptions to the CRSC shielding standards may only be granted by the Department of Health Services (the code text expressly identifies that agency as the only entity that can grant a variance). § 3102C.
- For equipment operating at different voltage ranges, the CRSC also includes operational and interlock requirements (e.g., additional interlocks and control-station location for equipment >150 kVp and warning signals for >500 kVp). Those operational requirements affect how barriers and controls are arranged but do not change the fundamental definitions of primary/secondary barrier. § 3104C.3 and related items.
If you need precise numerical attenuation (lead thickness, barrier transmission factors, design touchstone occupancy factors, workload, use factor, distances), the CRSC points you to Section 12‑31C‑101 (CRSC) for the technical calculations; those technical tables were not included in the retrieved files here.
Common mistakes
- Mislabeling: treating any shield that is not struck directly by the useful beam as a “primary” rather than a “secondary” — remember primary = attenuate the useful beam; secondary = attenuate stray (leakage/scatter). § 3101C.
- Forgetting the 1 foot (305 mm) border when laying out primary barrier areas — that border is required around the area that can be struck by the useful beam. § 3104C.1.
- Using an observation window or viewing glass that is less protective than the surrounding wall — windows must match surrounding barrier attenuation. § 3103C.2.
- Assuming the CRSC gives specific lead thickness or attenuation numbers in these definition sections — it does not. The actual attenuation design values and calculation method are in the referenced CRSC technical section (Section 12‑31C‑101). § 3102C.
Worked example — concrete scenario
Scenario: A diagnostic X‑ray tube (collimated useful beam) is located in a treatment room. The useful beam can strike a portion of the south wall that is 6 ft wide by 8 ft high. The operator control station sits behind a separate shielded booth adjoining that south wall.
- Identify the area struck by the useful beam: 6 ft × 8 ft = 48 ft². (This is the area directly exposed to the beam.)
- Add the required border: 1 foot (305 mm) on all sides (per § 3104C.1). Adding 1 ft around increases the struck-area envelope to (6 + 2) ft × (8 + 2) ft = 8 ft × 10 ft = 80 ft². That entire envelope must be provided with a primary protective barrier. § 3104C.1.
- Operator station: the booth must be arranged so the booth barrier intercepts the useful beam and any once‑scattered radiation — the booth wall or window must therefore be treated as a primary-level protective barrier; if a viewing window is used it must have attenuation equal to the adjacent barrier (per § 3103C.1 and § 3103C.2).
- Shielding design: to determine required material and thickness (lead, concrete, gypsum + lead, etc.), use the CRSC technical design procedure and tables in Section 12‑31C‑101 (CRSC). That calculation requires workload, use factor, distance to occupied spaces and occupancy factors — these technical inputs and the resulting attenuation numbers are not present in the retrieved excerpts and must be taken from Section 12‑31C‑101. § 3102C.
Result (code-level): label and construct the 8 ft × 10 ft envelope of the south wall as a primary protective barrier and ensure the operator booth/window provides attenuation equal to that barrier. Final thickness/assembly is determined by the Section 12-31C-101 calculations.
Related provisions
- § 3101C — Definitions: primary protective barrier, secondary protective barrier, stray radiation, useful beam.
- § 3102C — Radiation shielding barriers must meet Section 12‑31C‑101 (CRSC); Department of Health Services variance authority.
- § 3103C.1 — Operator station shielding must intercept the useful beam and single-scatter radiation.
- § 3103C.2 — Observation window attenuation equal to surrounding barrier.
- § 3104C.1 — Primary barriers required for all wall/floor/ceiling areas that can be struck by the useful beam plus 1 foot (305 mm) border.
- § 3104C.2–3104C.5 — Additional operational and interlock requirements for equipment operating above specified kVp thresholds (see equipment-specific items in § 3104C).
Code references
Grounded in the retrieved California Referenced Standards Code — click a citation to read the verbatim passage:
CRSC § 1.11. High relevance — show source text
CALIFORNIA BUILDING CODE – MATRIX ADOPTION TABLE
CHAPTER 31C – RADIATION
(Matrix Adoption Tables are nonregulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.)
Adopting agency BSC BSC-
CGSFM HCD Col6 Col7 DSA Col9 Col10 OSHPD Col12 Col13 Col14 Col15 Col16 Col17 BSCC DPH AGR DWR CEC CA SL SLC Adopting agency BSC BSC-
CGSFM 1 2 1/AC AC SS SS/CC 1 1R 2 3 4 5 6 6 6 6 6 6 6 6 6 Adopt entire chapter X Adopt entire chapter as
amended (amended
sections listed below)Adopt only those sections
that are listed belowChapter / Section The state agency does not adopt sections identified with the following symbol: The Office of the State Fire Marshal’s adoption of this chapter or individual sections is applicable to structures regulated by other state agencies pursuant to Section 1.11.
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31C [DPH] RADIATION
SECTION 3101C—SCOPE
For the purpose of this chapter, the following terms shall have the meaning indicated:
PRIMARY PROTECTIVE BARRIER is a barrier to attenuate the useful beam.
SECONDARY PROTECTIVE BARRIER is a barrier to attenuate stray radiation.
STRAY RADIATION is radiation not serving any useful purpose, which includes leakage and scattered radiation.
USEFUL BEAM is the radiation which passes through the window, aperture, cone or other collimating device of the tube housing.
SECTION 3102C—RADIATION SHIELDING BARRIERS
All radiation shielding barriers in rooms and enclosures housing machines shall meet the requirements of Section 12-31C-101, Chapter 12-31C, Part 12, California Referenced Standards Code. The Department of Health Services is the only agency that may grant a variance or exception to these standards.
SECTION 3103C—MEDICAL RADIOGRAPHIC AND PHOTOFLUOROGRAPHIC INSTALLATIONS
CRSC § 1.11. High relevance — show source text
The state agency does not adopt sections identified with the following symbol: The Office of the State Fire Marshal’s adoption of this chapter or individual sections is applicable to structures regulated by other state agencies pursuant to Section 1.11.
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31C [DPH] RADIATION
SECTION 3101C—SCOPE
For the purpose of this chapter, the following terms shall have the meaning indicated:
PRIMARY PROTECTIVE BARRIER is a barrier to attenuate the useful beam.
SECONDARY PROTECTIVE BARRIER is a barrier to attenuate stray radiation.
STRAY RADIATION is radiation not serving any useful purpose, which includes leakage and scattered radiation.
USEFUL BEAM is the radiation which passes through the window, aperture, cone or other collimating device of the tube housing.
SECTION 3102C—RADIATION SHIELDING BARRIERS
All radiation shielding barriers in rooms and enclosures housing machines shall meet the requirements of Section 12-31C-101, Chapter 12-31C, Part 12, California Referenced Standards Code. The Department of Health Services is the only agency that may grant a variance or exception to these standards.
SECTION 3103C—MEDICAL RADIOGRAPHIC AND PHOTOFLUOROGRAPHIC INSTALLATIONS
3103C.1 Operator station. The operator’s station at the control shall be behind a protective barrier either in a separate room, in a protected booth or behind a shield which will intercept the useful beam and any radiation which has been scattered only once.
3103C.2 Patient observation and communication. Provision shall be made for the operator to observe and communicate with the patient without leaving the shielded position at the control panel. When an observation window is used, it must provide radiation atten- uation equal to that required in the surrounding barrier.
SECTION 3104C—MEDICAL THERAPEUTIC X-RAY INSTALLATIONS
3104C.1 General. All wall, floor and ceiling areas that can be struck by the useful beam, plus a border of 1 foot (305 mm), shall be provided with primary protective barriers.
3104C.2 Equipment operating above 50 kVp. Equipment operating above 50 kVp shall conform with the following: 1. The control station shielding shall either be an integral part of the building or anchored to the building. 2. The control station shall be provided with a window having radiation attenuation equal to that required by the adjacent barrier, or a mirror system, or a closed-circuit television viewing screen. The patient area must be visible to the operator with- out having to leave the protected area during exposure.
CRSC § 3103C.1 High relevance — show source text
SECTION 3103C—MEDICAL RADIOGRAPHIC AND PHOTOFLUOROGRAPHIC INSTALLATIONS
3103C.1 Operator station. The operator’s station at the control shall be behind a protective barrier either in a separate room, in a protected booth or behind a shield which will intercept the useful beam and any radiation which has been scattered only once.
3103C.2 Patient observation and communication. Provision shall be made for the operator to observe and communicate with the patient without leaving the shielded position at the control panel. When an observation window is used, it must provide radiation atten- uation equal to that required in the surrounding barrier.
SECTION 3104C—MEDICAL THERAPEUTIC X-RAY INSTALLATIONS
3104C.1 General. All wall, floor and ceiling areas that can be struck by the useful beam, plus a border of 1 foot (305 mm), shall be provided with primary protective barriers.
3104C.2 Equipment operating above 50 kVp. Equipment operating above 50 kVp shall conform with the following: 1. The control station shielding shall either be an integral part of the building or anchored to the building. 2. The control station shall be provided with a window having radiation attenuation equal to that required by the adjacent barrier, or a mirror system, or a closed-circuit television viewing screen. The patient area must be visible to the operator with- out having to leave the protected area during exposure.
3104C.3 Equipment operating above 150 kVp. Equipment operating above 150 kVp shall conform to the following: 1. The treatment room shall be provided with interlocks so that when any door of the treatment room is opened, either the machine will shut off automatically or the radiation level within the room will be reduced to an average of not more than 2 milliroentgens per hour and a maximum of 10 milliroentgens per hour at a distance of one meter in any direction from the target. After such shutoff or reduction in output, it shall be possible to restore the machine to full operation only from the control panel. 2. The control station shall be within a protective booth or in an adjacent room.
3104C.4 A minimum of one door shall be provided with an auxiliary means for being opened in case of power failure or mechanical breakdown, where large power-driven doors offer the only access to the room.
3104C.5 A flashing red warning signal light energized only when the useful beam is on shall be located adjacent to the entrance(s) to a therapy room with equipment capable of operating above 500 kVp.
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CALIFORNIA BUILDING CODE – MATRIX ADOPTION TABLE
CHAPTER 31D – FOOD ESTABLISHMENTS
(Matrix Adoption Tables are nonregulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.)
California Referenced Standards Code High relevance — show source text
PG&E’s preferred PS arrangements are either: a) when the PS customer’s primary distribution line is underground (UG) and the POS is less than 500 feet from the property line, or b) when the PS customer’s primary distribution line is overhead (OH) and the protective device pole (if separate from the POS pole) is less than 50 feet from the property line.
- UG Conductor and POS < 500 Feet
If the PS customer’s primary line is underground and the POS is 500 feet or less from the property line, refer to Figure 1 on Page 12 and Figure 2 on Page 13. The following requirements apply:
A. The PS customer must provide a PG&E approved pad−mounted switchgear enclosure for PG&E’s revenue−metering equipment. See Section 12 on Page 13 for detailed revenue− metering requirements.
B. The PS customer must install primary protection at the POS. This protection may consist of a circuit breaker with phase and ground relays or, depending on the customer’s load, fuses may suffice. If PG&E determines that fuses will not coordinate with PG&E’s source−side protection, then the customer must use a circuit breaker. See Section 8A on Page 6 and Section 8C on Page 7 for circuit breaker and fuse requirements.
C. The PS customer must install conduit from the POS to PG&E’s primary distribution equipment location.
D. PG&E will pull one continuous run of cable and connect to the customer’s POS termination facility, not to exceed 500 feet (subject to an acceptable number of bends in the conduit).
- OH Conductor
If the PS customer’s primary line is overhead, then the first pole at the customer’s property line is the POS. Refer to Figure 3. The following requirements apply:
A. PG&E will install pole−top revenue−metering on the first pole on the PS customer’s property. See Engineering Standard 058779 Pole−Top Primary Metering Installation, (12 or 21 kV Line) for pole−top revenue− metering requirements.
B. The PS customer must install primary protection on the second pole on their property, not to exceed 50 feet from the revenue metering pole. This protection may consist of a recloser or, depending on the customer’s load, fuses may suffice. If PG&E determines that fuses will not coordinate with PG&E’s source−side protection, then the customer must use a recloser. See Section 8C on Page 7 for recloser requirements.
C. The PS customer second pole and the equipment installed on it, must maintain a minimum clearance of 10 feet from the PG&E revenue metering pole and any equipment, crossarms, and wires installed on it.
D. PG&E will interconnect its system with the customer’s system at the revenue−metering pole.
Section 4 Non−Preferred PS Arrangement Proposals
PS customers may propose a non−preferred PS arrangement. This typically occurs when the PS customer’s primary distribution line is UG and the proposed location for the primary switchgear is greater than 500 feet from the property line. PG&E will consider such proposals; however, non−preferred service arrangement proposals may take longer to
094676 Page 2 of 16 Rev. #00: 3/25/2022
CRSC § 704.5.1 High relevance — show source text
704.5.1 Secondary attachments to structural members. Where primary and secondary structural steel members require fire protection, any additional structural steel members having direct connection to the primary structural frame or secondary structural members shall be protected with the same fire-resistive material and thickness as required for the structural member. The protection shall extend away from the structural member a distance of not less than 12 inches (305 mm), or shall be applied to the entire length where the attachment is less than 12 inches (305 mm) long. Where an attachment is hollow and the ends are open, the fire-resistive material and thickness shall be applied to both exterior and interior of the hollow steel attachment.
704.6 Reinforcing. Thickness of protection for concrete or masonry reinforcement shall be measured to the outside of the reinforcement except that stirrups and spiral reinforcement ties are permitted to project not more than 0.5 inch (12.7 mm) into the protection.
704.7 Embedments and enclosures. Pipes, wires, conduits, ducts or other service facilities shall not be embedded in the required fire protective covering of a structural member that is required to be individually encased.
704.8 Impact protection. Where the fire protective covering of a structural member is subject to impact damage from moving vehicles, the handling of merchandise or other activity, the fire protective covering shall be protected by corner guards or by a substantial jacket of metal or other noncombustible material to a height adequate to provide full protection, but not less than 5 feet (1524 mm) from the finished floor.
Exception: Corner protection is not required on concrete columns in parking garages.
704.9 Exterior structural members. Load-bearing structural members located within the exterior walls or on the outside of a building or structure shall be provided with the highest fire-resistance rating as determined in accordance with the following:
- As required by Table 601 for the type of building element based on the type of construction of the building.
- As required by Table 601 for exterior bearing walls based on the type of construction.
- As required by Table 705.5 for exterior walls based on the fire separation distance.
704.10 Bottom flange protection. Fire protection is not required at the bottom flange of lintels, shelf angles and plates, spanning not more than 6 feet 4 inches (1931 mm) whether part of the primary structural frame or not, and from the bottom flange of lintels, shelf angles and plates not part of the structural frame, regardless of span.
704.11 Seismic isolation systems. Fire-resistance ratings for the isolation system shall meet the fire-resistance rating required for the columns, walls or other structural elements in which the isolation system is installed in accordance with Table 601. Isolation systems required to have a fire-resistance rating shall be protected with approved materials or construction assemblies designed to provide the same degree of fire resistance as the structural element in which the system is installed when tested in accordance with ASTM E119 or UL 263 (see Section 703.2).
Such isolation system protection applied to isolator units shall be capable of retarding the transfer of heat to the isolator unit in such a manner that the required gravity load-carrying capacity of the isolator unit will not be impaired after exposure to the standard time-temperature curve fire test prescribed in ASTM E119 or UL 263 for a duration not less than that required for the fire-resistance rating of the structure element in which the system is installed.
CRSC § 704.3.1. High relevance — show source text
FIRE AND SMOKE PROTECTION FEATURES
Primary structural members other than columns that do not support more than two floors or one floor and roof, or a load-bearing wall or a nonload-bearing wall more than two stories high, are permitted to be protected by the membrane of a fire-resistance-rated wall or horizontal assembly where the membrane provides the required fire-resistance rating.
Columns that meet the limitations of Section 704.3.1.
704.3 Protection of secondary structural members. Secondary structural members that are required to have protection to achieve a fire-resistance rating shall be protected by individual encasement protection, or by the membrane of a fire-resistance-rated wall or horizontal assembly where the membrane provides the required fire-resistance rating.
704.3.1 Light-frame construction. Studs, columns and boundary elements that are integral elements in walls of light-frame construction and are located entirely between the top and bottom plates or tracks shall be permitted to have required fire-resistance ratings provided by the membrane protection provided for the wall.
704.3.2 Horizontal assemblies. Horizontal assemblies are permitted to be protected with a membrane or ceiling where the membrane or ceiling provides the required fire-resistance rating and is installed in accordance with Section 711.
704.4 Truss protection. The required thickness and construction of fire-resistance-rated assemblies enclosing trusses shall be based on the results of full-scale tests or combinations of tests on truss components or on approved calculations based on such tests that satisfactorily demonstrate that the assembly has the required fire resistance.
704.5 Attachments to structural members. The edges of lugs, brackets, rivets and bolt heads attached to structural members shall be permitted to extend to within 1 inch (25 mm) of the surface of the fire protection.
704.5.1 Secondary attachments to structural members. Where primary and secondary structural steel members require fire protection, any additional structural steel members having direct connection to the primary structural frame or secondary structural members shall be protected with the same fire-resistive material and thickness as required for the structural member. The protection shall extend away from the structural member a distance of not less than 12 inches (305 mm), or shall be applied to the entire length where the attachment is less than 12 inches (305 mm) long. Where an attachment is hollow and the ends are open, the fire-resistive material and thickness shall be applied to both exterior and interior of the hollow steel attachment.
704.6 Reinforcing. Thickness of protection for concrete or masonry reinforcement shall be measured to the outside of the reinforcement except that stirrups and spiral reinforcement ties are permitted to project not more than 0.5 inch (12.7 mm) into the protection.
704.7 Embedments and enclosures. Pipes, wires, conduits, ducts or other service facilities shall not be embedded in the required fire protective covering of a structural member that is required to be individually encased.
704.8 Impact protection. Where the fire protective covering of a structural member is subject to impact damage from moving vehicles, the handling of merchandise or other activity, the fire protective covering shall be protected by corner guards or by a substantial jacket of metal or other noncombustible material to a height adequate to provide full protection, but not less than 5 feet (1524 mm) from the finished floor.
Exception: Corner protection is not required on concrete columns in parking garages.
CRSC § 704.1.1 High relevance — show source text
704.1.1 Supporting construction. The fire-resistance ratings of supporting structural members and assemblies shall be not less than the ratings required for the fire-resistance-rated assemblies supported by the structural members.
Exception: Structural members and assemblies that support fire barriers, fire partitions, smoke barriers and horizontal assemblies as provided in Sections 707.5, 708.4, 709.4 and 711.2, respectively.
704.2 Protection of the primary structural frame. Members of the primary structural frame that are required to have protection to achieve a fire-resistance rating shall be provided individual encasement protection by protecting them on all sides for the full length, including connections to other structural members, with materials having the required fire-resistance rating. Where a column extends through a ceiling, the encasement protection shall be continuous from the top of the foundation or floor/ceiling assembly below through the ceiling space to the top of the column.
Exceptions:
- Individual encasement protection on all sides shall be permitted on all exposed sides provided that the extent of protection is in accordance with the required fire-resistance rating, as determined in Section 703.
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FIRE AND SMOKE PROTECTION FEATURES
Primary structural members other than columns that do not support more than two floors or one floor and roof, or a load-bearing wall or a nonload-bearing wall more than two stories high, are permitted to be protected by the membrane of a fire-resistance-rated wall or horizontal assembly where the membrane provides the required fire-resistance rating.
Columns that meet the limitations of Section 704.3.1.
704.3 Protection of secondary structural members. Secondary structural members that are required to have protection to achieve a fire-resistance rating shall be protected by individual encasement protection, or by the membrane of a fire-resistance-rated wall or horizontal assembly where the membrane provides the required fire-resistance rating.
704.3.1 Light-frame construction. Studs, columns and boundary elements that are integral elements in walls of light-frame construction and are located entirely between the top and bottom plates or tracks shall be permitted to have required fire-resistance ratings provided by the membrane protection provided for the wall.
704.3.2 Horizontal assemblies. Horizontal assemblies are permitted to be protected with a membrane or ceiling where the membrane or ceiling provides the required fire-resistance rating and is installed in accordance with Section 711.
704.4 Truss protection. The required thickness and construction of fire-resistance-rated assemblies enclosing trusses shall be based on the results of full-scale tests or combinations of tests on truss components or on approved calculations based on such tests that satisfactorily demonstrate that the assembly has the required fire resistance.
704.5 Attachments to structural members. The edges of lugs, brackets, rivets and bolt heads attached to structural members shall be permitted to extend to within 1 inch (25 mm) of the surface of the fire protection.
CRSC § 3.2 Medium relevance — show source text
One of the fire endurance test criteria is the ability of a load-supporting element to carry its design load. The element will be deemed to have failed when the load can no longer be supported.
Failure usually results for two reasons. Some materials, particularly steel and other metals, lose much of their structural strength at elevated temperatures. Physical deflection of the supporting element, due to decreased strength or thermal expansion, causes a redistribution of the load forces and stresses throughout the element. Structural failure often results because the supporting element is not designed to carry the redistributed load.
Roof, floor and ceiling assemblies have primary (e.g., beams) and secondary (e.g., floor joists) structural members. Since the primary load-supporting elements span the largest distances, their deflection becomes significant at a stage when the strength of the secondary members (including the roof or floor surface) is hardly affected by the heat. As the secondary members follow the
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RESOURCE A—GUIDELINES ON FIRE RATINGS OF ARCHAIC MATERIALS AND ASSEMBLIES
deflection of the primary load-supporting element, an increasingly larger portion of the load is transferred to the secondary members.
When load-supporting elements are tested separately, the imposed load is constant and equal to the design load throughout the test. By definition, no distribution of the load is possible because the element is being tested by itself. Without any other structural members to which the load could be transferred, the individual elements cannot yield a higher fire endurance than they do when tested as parts of a floor, roof or ceiling assembly.
Rule 10: The load-supporting elements (beams, girders, joists, etc.) of a floor, roof or ceiling assembly can be replaced by such other load-supporting elements which, when tested separately, yielded fire endurances not less than that of the assembly.
This rule depends on Rule 9 for its validity. A beam or girder, if capable of yielding a certain performance when tested separately, will yield an equally good or better performance when it forms a part of a floor, roof or ceiling assembly. It must be emphasized that the supporting element of one assembly must not be replaced by the supporting element of another assembly if the performance of this latter element is not known from a separate (beam) test. Because of the load-reducing effect of the secondary elements that results from a test performed on an assembly, the performance of the supporting element alone cannot be evaluated by simple arithmetic. This rule also indicates the advantage of performing separate fire tests on primary load-supporting elements.
ILLUSTRATION OF HARMATHY’S RULES
Harmathy provided one schematic figure which illustrated his rules. It should be useful as a quick reference to assist in applying his rules.
FIGURE 3.2—DIAGRAMMATIC ILLUSTRATION OF HARMATHY’S TEN RULES [a]
IRE Col2 IRE IRE IRE IRE IRE t = Fire endurance
a. Reproduced from the May 1965 Fire Technology (Vol. 1, No. 2). Copyright National Fire Protection Association, Boston. Reproduced by permission.
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CRSC § 3.2 Medium relevance — show source text
This rule depends on Rule 9 for its validity. A beam or girder, if capable of yielding a certain performance when tested separately, will yield an equally good or better performance when it forms a part of a floor, roof or ceiling assembly. It must be emphasized that the supporting element of one assembly must not be replaced by the supporting element of another assembly if the performance of this latter element is not known from a separate (beam) test. Because of the load-reducing effect of the secondary elements that results from a test performed on an assembly, the performance of the supporting element alone cannot be evaluated by simple arithmetic. This rule also indicates the advantage of performing separate fire tests on primary load-supporting elements.
ILLUSTRATION OF HARMATHY’S RULES
Harmathy provided one schematic figure which illustrated his rules. It should be useful as a quick reference to assist in applying his rules.
FIGURE 3.2—DIAGRAMMATIC ILLUSTRATION OF HARMATHY’S TEN RULES [a]
IRE Col2 IRE IRE IRE IRE IRE t = Fire endurance
a. Reproduced from the May 1965 Fire Technology (Vol. 1, No. 2). Copyright National Fire Protection Association, Boston. Reproduced by permission.
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EXAMPLE APPLICATION OF HARMATHY’S RULES
The following examples, based in whole or in part upon those presented in Harmathy’s paper (see Bibliography entry 35), show how the rules can be applied to practical cases.
Example 1 :
Problem
A contractor would like to keep a partition which consists of a 3 [3] / 4 inch (95 mm) thick layer of red clay brick, a 1 [1] / 4 inch (32 mm) thick layer of plywood and a [3] / 8 inch (9.5 mm) thick layer of gypsum wallboard at a location where 2-hour fire endurance is required. Is this assembly capable of providing a 2-hour protection?
Solution
(1) This partition does not appear in the Appendix tables. (2) Bricks of this thickness yield fire endurances of approximately 75 minutes (Table 1.1.2, Item W-4-M-2). (3) The 1 [1] / 4 inch (32 mm) thick plywood has a finish rating of 30 minutes. (4) The [3] / 8 inch (9.5 mm) gypsum wallboard has a finish rating of 10 minutes. (5) Using the recommended values from the tables and applying Rule 1, the fire endurance (FI) of the assembly is larger than the sum of the individual layers, or FI > 75 + 30 + 10 = 115 minutes
Discussion
This example illustrates how the Appendix tables can be utilized to determine the fire resistance of assemblies not explicitly listed.
Example 2 :
Problem
(1) A number of buildings to be rehabilitated have the same type of roof slab which is supported with different structural elements.
CBC § 2025 Medium relevance — show source text
As in Rule 4, the reason lies in the heat transfer process, though the conductivity of the solid is much less dependent on the ambient temperature of the materials. The low thermal conductor creates a substantial temperature differential to be established across its thickness under transient heat flow conditions. This rule may not be applicable to materials undergoing physical-chemical changes accompanied by significant heat absorption or heat evolution.
Rule 7: The fire endurance of asymmetrical constructions depends on the direction of heat flow.
This rule is a consequence of Rules 4 and 6, as well as other factors. This rule is useful in determining the relative protection of corridors and walls enclosing an exit stairway from the surrounding spaces. In addition, there are often situations where a fire is more likely, or potentially more severe, from one side or the other.
Rule 8: The presence of moisture, if it does not result in explosive spalling, increases the fire endurance.
The flow of heat into an assembly is greatly hindered by the release and evaporation of the moisture found within cementitious materials such as gypsum, Portland cement or magnesium oxychloride. Harmathy has shown that the gain in fire endurance may be as high as 8 percent for each percent (by volume) of moisture in the construction. It is the moisture chemically bound within the construction material at the time of manufacture or processing that leads to increased fire endurance. There is no direct relationship between the relative humidity of the air in the pores of the material and the increase in fire endurance.
Under certain conditions there may be explosive spalling of low permeability cementitious materials such as dense concrete. In general, one can assume that extremely old concrete has developed enough minor cracking that this factor should not be significant.
Rule 9: Load-supporting elements, such as beams, girders and joists, yield higher fire endurances when subjected to fire endurance tests as parts of floor, roof or ceiling assemblies than they would when tested separately.
One of the fire endurance test criteria is the ability of a load-supporting element to carry its design load. The element will be deemed to have failed when the load can no longer be supported.
Failure usually results for two reasons. Some materials, particularly steel and other metals, lose much of their structural strength at elevated temperatures. Physical deflection of the supporting element, due to decreased strength or thermal expansion, causes a redistribution of the load forces and stresses throughout the element. Structural failure often results because the supporting element is not designed to carry the redistributed load.
Roof, floor and ceiling assemblies have primary (e.g., beams) and secondary (e.g., floor joists) structural members. Since the primary load-supporting elements span the largest distances, their deflection becomes significant at a stage when the strength of the secondary members (including the roof or floor surface) is hardly affected by the heat. As the secondary members follow the
RESOURCE A-10 2025 CALIFORNIA EXISTING BUILDING CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
RESOURCE A—GUIDELINES ON FIRE RATINGS OF ARCHAIC MATERIALS AND ASSEMBLIES
deflection of the primary load-supporting element, an increasingly larger portion of the load is transferred to the secondary members.
When load-supporting elements are tested separately, the imposed load is constant and equal to the design load throughout the test. By definition, no distribution of the load is possible because the element is being tested by itself. Without any other structural members to which the load could be transferred, the individual elements cannot yield a higher fire endurance than they do when tested as parts of a floor, roof or ceiling assembly.
CRSC § 2.95 Medium relevance — show source text
00|2.95|2.20|1.45|3.00|2.35|1.25|DR| |Cold-formed steel framing
(minimum penetration of steel
thickness plus 3 threads)|#8 screw into 33 mil steel or
thicker|8|3.00|2.55|1.60|0.60|3.00|1.80|DR|DR| |Cold-formed steel framing
(minimum penetration of steel
thickness plus 3 threads)|#8 screw into 33 mil steel or
thicker|12|3.00|1.80|DR|DR|3.00|0.65|DR|DR| |Cold-formed steel framing
(minimum penetration of steel
thickness plus 3 threads)|#10 screw into 33 mil steel|6|4.00|3.50|2.70|1.95|4.00|2.90|1.70|0.55| |Cold-formed steel framing
(minimum penetration of steel
thickness plus 3 threads)|#10 screw into 33 mil steel|8|4.00|3.10|2.05|1.00|4.00|2.25|0.70|DR| |Cold-formed steel framing
(minimum penetration of steel
thickness plus 3 threads)|#10 screw into 33 mil steel|12|4.00|2.25|0.70|DR|3.70|1.05|DR|DR| |Cold-formed steel framing
(minimum penetration of steel
thickness plus 3 threads)|#10 screw into 43 mil steel or
thicker|6|4.00|4.00|4.00|3.60|4.00|4.00|3.45|2.70| |Cold-formed steel framing
(minimum penetration of steel
thickness plus 3 threads)|#10 screw into 43 mil steel or
thicker|8|4.00|4.00|3.70|3.00|4.00|3.85|2.80|1.80| |Cold-formed steel framing
(minimum penetration of steel
thickness plus 3 threads)|#10 screw into 43 mil steel or
thicker|12|4.00|3.85|2.80|1.80|4.00|3.05|1.50|DR| |For SI: 1 inch = 25.4 mm, 1 pound per square foot (psf) = 0.0479 kPa, 1 pound per square inch = 0.00689 MPa.
DR = design required, o.c. = on center.
a. Cold-formed steel framing shall be minimum 33 ksi steel for 33 mil and 43 mil steel and 50 ksi steel for 54 mil steel or thicker.
b. Screws shall comply with the requirements of AISI S240.
c. Foam sheathing shall have a minimum compressive strength of 15 pounds per square inch in accordance with ASTM C578 or ASTM C1289.|For SI: 1 inch = 25.4 mm, 1 pound per square foot (psf) = 0.0479 kPa, 1 pound per square inch = 0.00689 MPa.
DR = design required, o.c. = on center.
a. Cold-formed steel framing shall be minimum 33 ksi steel for 33 mil and 43 mil steel and 50 ksi steel for 54 mil steel or thicker.
b.CRSC § 4.2. Medium relevance — show source text
All components comply with the requirements Mil-Std. 883C.
4.2. A quality control program is established by the manufacturer consisting of inspection and test of 100 percent of all components, either on an individual basis, as part of
a subassembly, or equivalent.
4.3. Each assembled production unit is subjected to a burn in test while in an alarm condition for 24 hours while connected to a source of rated nameplate voltage and
frequency in an ambient of at least 49°C (120°F) followed by an operational test the maximum temperature on a carbon resistor shall be not greater than 50°C during
the normal standby condition and not greater than 75°C during the alarm condition.|2025 CALIFORNIA REFERENCED STANDARDS CODE 153
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
PROTECTIVE SIGNALING SYSTEMS
TABLE 12-72-3G—OBSCURATION—OPTICAL DENSITY CHART
(Based on a 5-foot light beam)Col2 Col3 Col4 Col5 METER READING
(Microamperes)PERCENT PER FOOT OBSCURATION
OuTOTAL OBSCURATION
OdTOTAL OPTICAL DENSITY
ODtOPTIC DENSITY PER
FOOT
ODf100.0 0.0000 0.0000 0.0000 0.0000 99.5 0.1002 0.5001 0.0022 0.0004 99.0 0.2008 1.0001 0.0044 0.0009 98.5 0.3019 1.5001 0.0066 0.0013 98.0 0.4033 2.0001 0.0088 0.0018 97.5 0.5051 2.5002 0.0110 0.0022 97.0 0.6074 3.0002 0.0132 0.0027 96.5 0.7101 3.5002 0.0155 0.0031 96.0 0.8132 4.0003 0.0177 0.0036 95.5 0.9167 4.5003 0.0200 0.0040 95.0 1.0227 5.0003 0.0223 0.0045 94.5 1.1251 5.5004 0.0246 0.0049 94.0 1.2300 6.0004 0.0296 0.0054 93.5 1.3353 6.5004 0.0292 0.0058 93.0 1.4410 7.0005 0.0315 0.0063 92.5 1.5473 7.5005 0.0339 0.0068 92.0 1.6539 8.0005 0.0362 0.0072 91.5 1.7611 8.5005 0.0386 0.
Frequently asked questions
What is the fundamental difference between a primary and secondary protective barrier?
A primary protective barrier is intended to attenuate the useful beam (the beam the tube is intentionally directing), while a secondary protective barrier attenuates stray radiation (leakage and scatter). These definitions are in § 3101C.
Do observation windows need special treatment?
Yes — any observation window must provide radiation attenuation equal to that required in the surrounding barrier; windows are treated as part of the barrier. § 3103C.2.
How much extra area do I have to shield around the area struck by the useful beam?
Add a border of 1 foot (305 mm) around every wall, floor, and ceiling area that can be struck by the useful beam; that envelope is the primary barrier area. § 3104C.1.
Where do I find the actual attenuation (lead thickness or equivalent) numbers?
The CRSC requires that all shielding meet the technical requirements in Section 12‑31C‑101 of the CRSC. § 3102C points you to that section for calculations and tables; those technical values were not included in the retrieved excerpts.
Who can grant a variance from these shielding standards?
Only the Department of Health Services may grant a variance or exception to these standards, per § 3102C.
More in California Referenced Standards Code
- Administration and scope — CRSC Chapter 12 overview
- Air filter standards (Chapter 12‑71)
- Building and facility access / accessibility standards (Chapters 12‑11A, 12‑11B)
- Engineering regulations — quality and design of construction materials (12‑16 series)
- Exits and means of egress (Chapters 12‑10 series)
- Protective signaling systems and detectors (Chapters 12‑72‑1, ‑2, ‑3)
- Radiation shielding standards (Chapter 12‑31C)
- Referenced standards index / cross‑reference table (Part 12 listing of referenced standards)
- Releasing systems for security bars (egress-release standards)
- Standards for insulating materials (Chapter 12‑13)
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