High Fire-Threat District: what Tier 2 and Tier 3 change for vegetation work

GO 95 Rule 21.2-D defines the High Fire-Threat District as Zone 1 of the USFS and CAL FIRE tree mortality map plus Tier 2 and Tier 3 of the CPUC Fire-Threat Map. Vegetation clearance does not change between the tiers. The Rule 18A correction clock does: six months in Tier 3, twelve in Tier 2.

Two 12 kV distribution spans, both rural, both on brush-covered ground, both measured at 30 inches to the nearest limb on the same August afternoon. One sits in Tier 2 of the High Fire-Threat District and the other in Tier 3. The clearance requirement is identical on both, the time-of-trim guideline is identical on both, and the patrol interval is identical on both.

What separates them is a due date: six months on one and twelve on the other, and only if the person who wrote up the finding characterized it a particular way. That is very nearly the whole of what the tier boundary does to vegetation work, and it is not what most people expect the answer to be.

The definition is three lines and two maps

GO 95 Rule 21.2 defines four kinds of district. Urban, rural and loading districts get a sentence each. The fourth is the one that scopes California's fire-safety regulations, and it is a list of pointers:

D. High Fire-Threat District means those areas comprised of the following: (1) Zone 1 is Tier 1 of the latest version of the United States Forest Service (USFS) and CAL FIRE's joint map of Tree Mortality High Hazard Zones (HHZs). (Note: The Tree Mortality HHZs Map may be revised regularly by the USFS and CAL FIRE.) (2) Tier 2 is Tier 2 of the CPUC Fire-Threat Map. (3) Tier 3 is Tier 3 of the CPUC Fire-Threat Map.

The note at the foot of the rule reads "Revised December 21, 2017 by Decision 17-12-024." That is the entire operative definition. It names no acreage, no fuel type, no wind threshold and no elevation. It sets no criteria of its own at all, and it does not contain the words elevated or extreme that everyone uses when describing the tiers.

Those words come from the decisions behind the map, not from GO 95. D.25-01-037, issued January 31, 2025, restates them. Tier 2 is where "there is an elevated risk (including likelihood and potential impacts on people and property) from wildfires associated with overhead utility power lines," and Tier 3 is where that risk is "extreme."

Tier 3, the decision adds, "is distinguished from Tier 2 by having the highest likelihood of utility-associated fire initiation and growth that would impact people or property, and where the most restrictive utility regulations are necessary to reduce utility fire risk."

So the tier of a given span is a question about a GIS layer, and nothing in the rule invites judgment about it. The pre-2018 fire-threat footnote in GO 165 used to say the opposite in as many words.

It instructed that the map "is to be used to establish approximate boundaries and Utilities should use their own expertise and judgment to determine if local conditions require them to adjust the boundaries of the map." That sentence is gone from the December 2017 text. What replaced it is a pointer to Rule 21.2-D and a polygon.

Where the tier words actually appear

D.17-12-024 amended exactly six things in General Order 95: Rule 18, Rule 21.2, Rule 35, Rule 38, Rule 80.1 and the Appendix E guidelines. The Commission's own rule browser lists those six and nothing else. Add GO 165's Table 1 and the inventory of provisions that turn on the district is complete:

Provision	Whole district	Tier 2 against Tier 3
Rule 21.2-D	defines it	names them
Rule 35, Table 1, Case 14, footnote (hhh)	radial clearance minimum	no difference
Appendix E guidelines to Rule 35	time-of-trim guideline	no difference
Rule 18A, Level 2	prioritization factor	12 months against six
Rule 38	---	10 percent against 5
Rule 80.1-A(1)	---	2 and 10 years against 1 and 5
GO 165, Table 1, footnote (1)	---	no difference

Two of the four rows that split the tiers are outside vegetation work entirely. Rule 38 governs the clearance of wires from other wires. It holds the Table 2 values to a reduction limit that tightens mid-span in Tier 3:

... shall in no case be reduced more than 10 percent, except mid-span in Tier 3 of the High Fire-Threat District where they shall be reduced by no more than 5 percent, because of temperature and loading as specified in Rule 43.

That is conductor sag against conductor sag, not conductor against tree. Rule 80.1-A(1) caps inspection intervals for communication lines on joint use poles carrying supply circuits, at two years and ten in Tier 2 against one and five in Tier 3. A separate subject is what those two words mean on the communications side of a shared pole.

That leaves one row in the vegetation stack that distinguishes Tier 2 from Tier 3, and two rows that do not.

The clearance does not change at the tier line

Table 1, Case 14 is the enforceable minimum inside the district, and it arrives there through a single footnote. Footnote (hhh) reads, in full:

The High Fire-Threat District is defined in GO 95, Rule 21.2-D.

There is no second footnote splitting the case by tier, and no tier appears anywhere in the Case 14 row. So the 48 inches Case 14 requires of a 12 kV conductor, the 72 inches footnote (fff) requires between 72 and 110 kV, and the 120 inches it requires above that are the same numbers in Tier 2, in Tier 3 and in Zone 1. The case, the columns and the two places the table gives a formula instead of a distance belong to their own page.

The time-of-trim side behaves the same way. Appendix E prints its recommended clearances in two columns, headed "Case 13 of Table 1" and "Case 14 of Table 1." One column for outside the district and one for inside it, with no third column and no tier.

D.17-12-024 raised that inside column sharply on December 21, 2017: 6.5 feet became 12 at 2,400 volts to 72 kV, 10 became 20 between 72 and 110 kV, and 20 became 30 above 110 kV and again above 300 kV. A crew that had been cutting a 12 kV span in a Southern California fire-threat zone to 6.5 feet was cutting the same span to 12 feet afterward, and the increase applied to every part of the new district at once.

Appendix E's own status did not change with the numbers. Its clearances remain "recommended minimum clearances that should be established, at time of trimming, between the vegetation and the energized conductors and associated live parts where practicable." The gap between the figure on the trim specification and the figure a citation is written against opens the same way inside the district as outside it, only wider.

The one thing that does change is a due date

Rule 18A requires every company to run an auditable maintenance program and to sort nonconformances into three priority levels. Location is one of the six listed factors the prioritization is built on, and the rule spells out which location it means: "Location, including whether the Safety Hazard or nonconformance is located in the High Fire-Threat District." At that point the rule is still district-wide. The tier appears one paragraph later, in the ceiling Rule 18A puts on a Level 2 correction period.

That period is set "at the time of identification by a qualified company representative," subject to four caps. Two of the four name a tier: six months for "nonconformances that create a fire risk located in Tier 3 of the High Fire-Threat District," and twelve months for the same description of a nonconformance in Tier 2. The remaining two are twelve months where worker safety is compromised, and 59 months for everything else at Level 2.

Two features of that provision decide more than the tier does.

The first is that the clock is a ceiling on someone else's judgment, not a schedule. A qualified company representative sets the period, and the tier only caps what that person may set. A Tier 3 finding given nine months is a nonconformance with Rule 18A on its face, and a Tier 3 finding given 90 days is compliant with it, but the 90 days is the company's own commitment and is auditable as such.

The second is the qualifier "that create a fire risk." The six and twelve month caps do not attach to every nonconformance in a tier. They attach to nonconformances characterized as creating a fire risk. A Level 2 clearance finding in Tier 2 that nobody characterized that way falls into the residual category and gets 59 months, which is nearly five years.

The tier alone does not set the clock; the tier plus a fire-risk characterization made by a named person on a named date does. That characterization is the single most consequential field on a Tier 2 or Tier 3 vegetation finding, and it is one an evaluator can check against the file in about a minute.

Set the two spans from the opening against that. Same voltage, same 30 inch reading, same 48 inch Case 14 requirement, same 18 inch shortfall. If both findings are characterized as creating a fire risk, the Tier 3 span is due in six months and the Tier 2 span in twelve. If neither is, both are due in 59. Rule 18A's record standard and the ten year retention that goes with it apply identically in either case.

Zone 1 is inside the district and outside both tiers

Zone 1 is the part of Rule 21.2-D that most compliance programs handle worst, because it is in the district for one purpose and absent from the tiers for several others.

Case 14 reaches it. Footnote (hhh) points at Rule 21.2-D as a whole, and Zone 1 is subsection (1) of that rule. So a 12 kV span in Zone 1 carries the same 48 inch minimum and the same 12 foot Appendix E guideline as a span in Tier 3. Rule 18A's prioritization factor reaches it too, since that factor names the district rather than a tier.

The tier-keyed provisions do not. Rule 18A's Level 2 fire-risk caps name Tier 3 and Tier 2 and stop, so a fire-risk Level 2 nonconformance in Zone 1 falls to the 59 month residual category. GO 165's Table 1 footnote (1), in the December 2017 text, reads "Patrol inspections in rural areas shall be increased to once per year in Tier 2 and Tier 3 of the High Fire-Threat District.

(See GO 95, Rule 21.2-D)," so a rural Zone 1 circuit stays on the two year patrol interval. Rule 80.1-A(1) applies "In Tiers 2 and 3," so a communication attachment in Zone 1 has no numeric interval. Rule 38's mid-span allowance names Tier 3 only.

Two facts about the underlying layer keep this from being a large practical exposure, and both are worth having in writing before an auditor raises it. The CPUC's published Zone 1 layer states that "the Tier 1 HHZs layer is last updated by CAL FIRE for year 2020," notwithstanding that Rule 21.2-D incorporates the latest version of a map the Commission does not own or maintain.

And the same layer states the convention the published composite uses where the sources overlap: "Majority of areas in this layer overlap with HFTD Tier 2 or Tier 3.

When overlap occurs, the established priority is that Tier 3 overwrites Tier 2 which overwrites Tier 1 HHZs." That is a cartographic rule in the CPUC's own GIS layer, not a provision of GO 95, and Rule 21.2-D states no precedence at all. Its practical effect is that a polygon showing as Zone 1 on the composite map is one that neither tier covers, which is exactly the ground where the tier-keyed clocks run out.

Which tier a span is in, and as of what date

The CPUC Fire-Threat Map is not a document the Commission adopted in a decision. PG&E and SDG&E submitted it jointly for approval on January 5, 2018, and it was approved on January 19, 2018 by staff disposition of Joint Advice Letter 5211-E (PG&E) and 3172-E (SDG&E). D.17-01-009, as modified by D.17-06-024, "set an expectation that the map would remain unchanged for ten years," in the words of the Commission's own later description of it.

It has not been entirely unchanged. The CPUC publishes a layer named HFTD_Tiers2_3_Changes whose description reads "Since the creation of HFTD, there are two minor changes to the original HFTD map." Both are additions, and both carry a full General Order implementation date:

Change	Type	Full GO implementation
SCE PFM	Addition	June 30, 2021
Healdsburg correction	Addition	August 19, 2021

The second date is also the version date of the current published map, which the Commission distributes as CPUC HFTD v.3, 08.19.2021. So a span that a 2019 record described as outside the district may have been inside Tier 2 since June 30, 2021, and the transition has a date on it rather than a season. That matters directly to the clearance history: Case 14 replaced Case 13 on that span from the implementation date forward, and the correction clocks attached from the same day.

For a specific location, the authoritative sources are the GIS files the Safety and Enforcement Division publishes under D.17-01-009 and the Commission's own web viewer at ia.cpuc.ca.gov/firemap. The layer carries a disclaimer worth reading before it is repurposed: "All data and information portrayed on the CPUC Fire-Threat Map are for the expressed use called for in D.17-12-024. Any other use of this map is not the responsibility of nor endorsed by the CPUC or its supporting Independent Review Team."

One caution about secondary copies. The Commission's HTML rule browser still serves the June 2013 version of GO 165's Table 1, complete with the superseded footnote listing Imperial, Los Angeles, Orange, Riverside, Santa Barbara, San Bernardino, San Diego and Ventura counties and the FRAP map. The operative text is the December 2017 PDF. A program built by reading the browser instead of the order will have the wrong trigger for its rural patrol interval and will not know it.

How the boundary moves, and who can move it

Neither tier boundary is fixed for ten years in the sense of being unchallengeable. Two routes exist and both have been used.

The first is a petition for modification. Southern California Edison filed one on August 19, 2019, asking that areas near its service territory be added to Tier 2. In D.20-12-030 the Commission approved the proposal with modifications, rejecting six of the proposed polygons and accepting the rest, and did not otherwise change the frequency or the means of updating the map. That is the "SCE PFM" row in the change layer, and the fire-safety regulations applied to the newly designated areas from June 30, 2021.

The second runs through the wildfire mitigation plan. Public Utilities Code section 8386(d)(17) requires the plan to include the utility's own account of ground the map may have missed:

identification of any geographic area in the electrical corporation's service territory that is a higher wildfire threat than is currently identified in a commission fire threat map, and where the commission should consider expanding the high fire threat district based on new information or changes in the environment.

The paragraph sat at 8386(c)(17) until SB 254 renumbered it, effective September 19, 2025, so decisions and plans written before that date cite the older subdivision. It is the statutory hook that produced SCE's petition in the first place.

What does not exist is a faster general cycle. On April 19, 2023 the Public Advocates Office petitioned to modify D.17-01-009, D.17-12-024 and D.20-12-030 to require updates every five years, driven by each utility's own risk modeling. D.25-01-037 denied it on January 30, 2025, for failure to justify the relief, observing that "parties already have a means to request changes to the High Fire-Threat District boundaries prior to our consideration of a statewide update, irrespective of the frequency."

The same decision adds a clarification that settles a recurring argument in vegetation program documents: "while the petition refers to 'HFTD maps,' suggesting each IOU has its own HFTD map, the Commission only approved one statewide High Fire-Threat District." A utility's internal fire-risk map, however sophisticated, is not the HFTD and does not change which case of Table 1 applies to a span. R.15-05-006 remains open.

The district is not the State Responsibility Area

The most expensive confusion around the tiers is not between Tier 2 and Tier 3. It is between the High Fire-Threat District and the other fire geographies a California span can sit in, which are drawn by different agencies for different purposes and do not coincide.

The district is a CPUC construct, scoped to CPUC rules. The State Responsibility Area is a Board of Forestry construct that determines where PRC 4292 and 4293 apply, and CAL FIRE's Fire Hazard Severity Zones are a third product again.

A span can be Tier 3 and in a Local Responsibility Area, or in a State Responsibility Area and outside the district entirely, and each combination produces a different pair of obligations. Where the GO 95 and PRC 4293 numbers diverge, and where Case 14 restates the statute exactly is the page that works that through on a single conductor.

One Public Resources Code section does reach into the Commission's geography. PRC 4295.5 grants a right of entry in areas "designated by the Public Utilities Commission as a high fire-threat district" as well as in State Responsibility Areas, which makes the tier boundary relevant to access when a landowner will not permit the work.

Outside that section, the tiers do not appear in the CAL FIRE stack at all: 14 CCR 1250 through 1258 is written on the State Responsibility Area, and PRC 4293's clearances turn on land cover and fire season rather than on any CPUC map.

What the record has to name

A tier is a claim about a location, and like a measured distance it is only auditable if the file says where it came from.

Four elements make one checkable. The tier itself, as Tier 2, Tier 3 or Zone 1 rather than "in the HFTD," because the correction clock is unavailable without it. The map version the determination was made against, which for anything current is CPUC HFTD v.3 of August 19, 2021, since a span added by the SCE petition was outside the district in a 2020 record and inside it in a 2022 one.

The fire-risk characterization, with the qualified representative who made it and the date, because that is what converts a Level 2 finding from the 59 month residual into a six or twelve month obligation. And the correction period actually set, which is the company's own number under the tier's ceiling and is the number an audit will hold it to.

Put those against the two spans this page opened with. "12 kV, Tier 3 per CPUC HFTD v.3, 30 inches at closest approach against Case 14 column E, fire risk, Level 2 set at 90 days by [name] on August 14, 2026" is a finding a stranger can test end to end. "Span in high fire area, needs trim" names none of the four, and there is no way to tell from it whether the six month ceiling was ever engaged.

The shape of a clearance record that survives being read a year later and the retention period attached to every piece of it are their own subjects. The tier's contribution to both is that it is the one field that changes a deadline without changing a single measurement.

Further reading

• Overhead power line clearance by voltage in California: The Case 14 numbers the district switches on, column by column.

• CPUC GO 95 Rule 35: the vegetation clearance rule, explained: The rule Case 14 sits inside, and the Rule 18A program that carries its clocks.

• GO 165 inspection cycles, and the one thing they do not cover: The single inspection interval in GO 165 that moves with the fire-threat tier.

Frequently asked questions

What is the High Fire-Threat District?

GO 95 Rule 21.2-D defines it as three areas taken together: Zone 1, which is Tier 1 of the latest version of the United States Forest Service and CAL FIRE joint map of Tree Mortality High Hazard Zones; Tier 2 of the CPUC Fire-Threat Map; and Tier 3 of the CPUC Fire-Threat Map. The rule was added December 21, 2017 by Decision 17-12-024, and it contains no other criteria.

Does the required vegetation clearance differ between Tier 2 and Tier 3?

No. GO 95 Table 1, Case 14 applies through footnote (hhh), which says only that the High Fire-Threat District is defined in Rule 21.2-D. The Appendix E time-of-trim guidelines are printed in one column headed Case 14 of Table 1. Both are district-wide, so a 12 kV span carries the same 48 inch minimum and the same 12 foot guideline in Tier 2 and in Tier 3.

What actually changes between Tier 2 and Tier 3?

Inside the vegetation stack, one due date. GO 95 Rule 18A caps a Level 2 correction at six months for nonconformances that create a fire risk located in Tier 3, and at 12 months for the same nonconformance in Tier 2. Two other provisions split the tiers and neither is about vegetation: Rule 38 tightens the mid-span wire-to-wire sag allowance in Tier 3, and Rule 80.1-A(1) sets shorter inspection intervals in Tier 3 for communication lines on joint use poles.

How often is the CPUC Fire-Threat Map updated?

It was approved January 19, 2018 by staff disposition of Joint Advice Letter 5211-E and 3172-E, and D.17-01-009 as modified by D.17-06-024 set an expectation that it would remain unchanged for ten years. Two changes have been recorded since, both taking effect in 2021. On January 30, 2025 the Commission denied a petition by the Public Advocates Office to move to five year updates, in D.25-01-037.