diff --git a/changelog.d/1395-fires-tool-acquired-time.md b/changelog.d/1395-fires-tool-acquired-time.md
new file mode 100644
index 000000000..17d74e481
--- /dev/null
+++ b/changelog.d/1395-fires-tool-acquired-time.md
@@ -0,0 +1,6 @@
+- Report a fire detection's acquisition time as a UTC timestamp in
+  `get_active_fires`. The tool joined FIRMS's unpadded date and time, so a
+  00:45 UTC detection read "2026-01-01 45"; it now reads
+  `2026-01-01T00:45:00.000Z`. Missing or invalid dates and times remain
+  unknown rather than rolling into another calendar day
+  (Rudy Celekli, @rudycelekli, #1395).
diff --git a/docs/CURRENT-STATE.md b/docs/CURRENT-STATE.md
index 921604789..b444589b9 100644
--- a/docs/CURRENT-STATE.md
+++ b/docs/CURRENT-STATE.md
@@ -1984,6 +1984,9 @@ accessible name remains "Don't show this again". Control behavior is unchanged.
 ## FIRMS source status
 
 The FIRMS CSV parser rejects impossible acquisition calendar dates before the proxy filters records to the trailing 24 hours, while retaining valid UTC acquisition times.
+The `get_active_fires` tool reports acquisition times as UTC ISO timestamps,
+including zero-padded hours and minutes; missing or invalid dates and times
+remain `null`, including impossible calendar dates from a custom source.
 
 The FIRMS proxy records source success after appending its rows. If aggregation
 throws, that source reports failure without a contradictory success entry.
diff --git a/src/tools/queries/hazards.js b/src/tools/queries/hazards.js
index 475df97ba..2b11c639c 100644
--- a/src/tools/queries/hazards.js
+++ b/src/tools/queries/hazards.js
@@ -5,6 +5,24 @@ import { defineTool, ToolError } from '../catalog.js';
 import { AREA_SCHEMA, areaContains, resolveArea } from '../area.js';
 import { LIMIT_SCHEMA, capRows, countNoun, isoTime } from '../results.js';
 
+function acquiredMsUtc(acqDate, acqTime) {
+  if (typeof acqDate !== 'string' || !/^\d{4}-\d{2}-\d{2}$/.test(acqDate))
+    return NaN;
+  const timeText = String(acqTime ?? '').trim();
+  if (!/^\d{1,4}$/.test(timeText)) return NaN;
+  const hhmm = timeText.padStart(4, '0');
+  const hours = Number(hhmm.slice(0, 2));
+  const minutes = Number(hhmm.slice(2, 4));
+  if (hours > 23 || minutes > 59) return NaN;
+  const timestamp = Date.parse(
+    `${acqDate}T${hhmm.slice(0, 2)}:${hhmm.slice(2, 4)}:00.000Z`,
+  );
+  return Number.isFinite(timestamp) &&
+    new Date(timestamp).toISOString().slice(0, 10) === acqDate
+    ? timestamp
+    : NaN;
+}
+
 export const getEarthquakes = defineTool({
   name: 'get_earthquakes',
   title: 'Recent earthquakes',
@@ -114,8 +132,7 @@ export const getActiveFires = defineTool({
           lon: fire.lon,
           frp_mw: fire.frp ?? null,
           confidence: fire.confidence ?? null,
-          acquired:
-            [fire.acqDate, fire.acqTime].filter(Boolean).join(' ') || null,
+          acquired: isoTime(acquiredMsUtc(fire.acqDate, fire.acqTime)),
           satellite: fire.satellite ?? null,
           day_night: fire.daynight ?? null,
         })),
diff --git a/src/tools/queries/hazards.test.mjs b/src/tools/queries/hazards.test.mjs
new file mode 100644
index 000000000..fa17158dd
--- /dev/null
+++ b/src/tools/queries/hazards.test.mjs
@@ -0,0 +1,46 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import { composeCatalog } from '../catalog.js';
+import { getActiveFires } from './hazards.js';
+
+const catalogWith = (fires) =>
+  composeCatalog({
+    tools: [getActiveFires],
+    services: { fires: { getSnapshot: async () => ({ fires }) } },
+  });
+
+test('a fire acquired at 00:45 UTC reads as 00:45, not "45"', async () => {
+  const result = await catalogWith([
+    { lat: 24, lon: 121, frp: 5, acqDate: '2026-01-01', acqTime: '45' },
+  ]).call('get_active_fires', { area: { bbox: [120, 23, 122, 25] } });
+  assert.equal(result.data.rows[0].acquired, '2026-01-01T00:45:00.000Z');
+});
+
+test('fire acquisition timestamps reject impossible calendar dates', async () => {
+  for (const acqDate of [
+    '2026-02-29',
+    '2026-02-30',
+    '2026-04-31',
+    '1900-02-29',
+    '2026-13-01',
+    '2026-01-00',
+  ]) {
+    const result = await catalogWith([
+      { lat: 24, lon: 121, acqDate, acqTime: '45' },
+    ]).call('get_active_fires', { area: { bbox: [120, 23, 122, 25] } });
+    assert.equal(result.data.rows[0].acquired, null, acqDate);
+  }
+});
+
+test('fire acquisition timestamps preserve valid leap days and UTC times', async () => {
+  for (const [acqDate, acqTime, expected] of [
+    ['2024-02-29', '45', '2024-02-29T00:45:00.000Z'],
+    ['2000-02-29', 0, '2000-02-29T00:00:00.000Z'],
+    ['2026-04-30', '2359', '2026-04-30T23:59:00.000Z'],
+  ]) {
+    const result = await catalogWith([
+      { lat: 24, lon: 121, acqDate, acqTime },
+    ]).call('get_active_fires', { area: { bbox: [120, 23, 122, 25] } });
+    assert.equal(result.data.rows[0].acquired, expected);
+  }
+});
diff --git a/src/tools/queries/queries.test.mjs b/src/tools/queries/queries.test.mjs
index b64f5e009..5f53cf9e8 100644
--- a/src/tools/queries/queries.test.mjs
+++ b/src/tools/queries/queries.test.mjs
@@ -125,7 +125,7 @@ test('fires need an area and report a missing key as unavailable', async () => {
     result.data.rows.map((row) => row.frp_mw),
     [40, 12],
   );
-  assert.equal(result.data.rows[1].acquired, '2026-01-01 0130');
+  assert.equal(result.data.rows[1].acquired, '2026-01-01T01:30:00.000Z');
 
   const keyless = composeCatalog({
     tools: coreTools,