23 June 2026 · 7 min read

The two clocks: notifying DOE of an excess emission and a CEMS failure

Enforcing the Clean Air Regulations 2014 — Part 3 of 5. A series for regulators and compliance staff, drawn from the DOE CEMS Guidelines (Version 8, 2025), which we helped develop.

Part 1 set out what compliance means — no daily average above the ELV, no half-hourly average above twice it. Part 2 settled which numbers count — only valid averages. This part answers the question both of those raise but neither resolves: the moment a valid exceedance happens, or the CEMS stops working — what must the operator actually do, and how fast?

The Clean Air Regulations 2014 give two answers, and they run on two very different clocks.

The two clocks

Regulation 17 sets two separate notification duties, with two separate triggers and two separate deadlines:

(6) In the event where emission standards exceed the prescribed limit values, the owner or occupier of such premises shall notify the Director General within twenty-four hours from the discovery of the excess emission.

(7) In the event a monitoring device fails to operate, the owner or occupier of the premises shall notify the Director General not later than one hour from the occurrence of such failure.

So a breach of the limit buys you twenty-four hours. A broken monitor gives you one. The tighter deadline is reserved for the failure — because a CEMS that isn’t measuring is a facility the regulator is, for that window, blind to.

The two notification clocks under Regulation 17 Two panels. Left: an excess emission must be notified within 24 hours from discovery, under Regulation 17(6). Right: a CEMS failure must be notified within one hour from the occurrence, under Regulation 17(7). Two duties, two clocks the trigger decides which deadline applies EXCESS EMISSION CEMS FAILURE 24 HOURS 1 HOUR from the discovery of the excess from the failure occurring Reg 17(6) Reg 17(7)
The deadline turns entirely on the trigger: an exceedance of a valid limit (24 hours) versus a monitor that has stopped working (one hour).

When does the clock start?

The wording is precise, and the two triggers start counting from different events.

For an excess emission, the clock starts at discovery. An excess emission, as Part 1 set out, is an exceedance of the applicable ELV as shown by a valid measurement — in CAR 2014 terms, a daily average above the ELV or a half-hourly average above twice it. Because the daily figure is only known once the day’s valid half-hours are evaluated, “discovery” is the point at which that evaluation reveals the breach — not necessarily the instant the stack ran high.

For a CEMS failure, the clock starts at the occurrence of the failure — the moment the monitoring device fails to operate. There’s no evaluation step to wait for: a CEMS that has gone down is down, and the hour runs from then.

That difference matters in practice. The excess-emission duty depends on an operator running its evaluations promptly and honestly; the failure duty depends on someone noticing the monitor is offline quickly. The DOE System for CEMS (the iRemote platform) helps on both fronts — it carries an alert feature for excess emissions, and a gap in transmitted data is itself a visible signal that a device may have failed.

Don’t confuse these with the neighbouring duties

Two other notification rules sit close by and are easy to muddle with the CEMS clocks:

  • Failure of the air pollution control system (Reg 8). If the abatement plant itself — not the monitor — fails, the Director General must be notified not later than one hour from the occurrence. Same one-hour deadline as a CEMS failure, but a different trigger: the scrubber or bag-filter going down, rather than the analyser.
  • Accidental emission (Reg 21). An accidental emission must be reported to the Director General immediately upon discovery — no fixed-hour window, the standard is immediately.

Keeping them straight is part of the job: a single incident can trip more than one duty at once. A control-system failure that drives the stack over its limit, for instance, can engage the Reg 8 one-hour clock and the Reg 17(6) twenty-four-hour clock together.

How you actually notify: the report and where it goes

The Guidelines turn these statutory deadlines into a concrete procedure. Under §6.2, notification is made to the state or branch DOE, using the standard Failure and Excess Emission Report Format at Appendix 4:

  • §6.2.3 — Report of excess emission. Where a half-hourly average exceeds 2× ELV or a daily average exceeds the ELV, the operator notifies DOE within 24 hours of the occurrence, on Appendix 4.
  • §6.2.4 — Report of CEMS failure. Where the CEMS fails to operate, the operator notifies DOE not later than one hour, on Appendix 4.
  • §6.2.5 — Source or CEMS shutdown. This one is easy to overlook: a planned stop — scheduled maintenance, a change of parts, or ceasing operation — must also be notified to DOE. Not every notification is an emergency; predictable downtime has to be declared too.

The Appendix 4 report is not a one-line email. Before you file, it helps to know what it asks for — the format is built around five parts:

What the report asks for · Appendix 4 of the Guidelines

APremise & installationCompany, plant and contact details; the equipment, stack and installation IDs; and operating hours.
BSource of pollutantStack ID, the parameters affected, the cause of the incident, and a chronology of the case.
CStatement of excess emissionsFor each event: date, start and end time, duration, reason (start-up, soot-blowing, control-equipment problem), and corrective action.
DAPCS / CEMS failureThe problem, the corrective action taken, and the expected date to resume operation.
EDeclarationA signed certification that the information is true, accurate and complete — and an acknowledgement that failure to resolve the situation is an offence under CAR 2014.
The authoritative form is Appendix 4 of the DOE CEMS Guidelines. Have these ready before the clock runs out.

That last section is the one operators underestimate. By signing, the operator doesn’t just report the event — it commits to corrective action and puts its name to the acknowledgement that an unresolved problem is an offence under CAR 2014. Notifying is not an admission that closes the matter; it opens a documented corrective process the regulator can follow and hold the facility to.

Why this matters for enforcement

For anyone assessing a facility’s conduct, the notification duties are as enforceable as the limits themselves:

  • The duty to notify is independent of the breach. An operator can be non-compliant for failing to notify on time even where the underlying excess was brief or quickly corrected. The clock is a legal obligation in its own right.
  • The timestamps tell their own story. The gap between when an exceedance was discoverable (the data evaluation) — or when a monitor went dark — and when the report landed is something a regulator can check directly against the 24-hour and one-hour limits.
  • Silence around downtime is a red flag. With scheduled shutdowns also requiring notification, unexplained gaps in the record aren’t neutral. Read alongside the validity rules, they point either to a CEMS that isn’t being maintained or to a duty that wasn’t met.

With the limits (Part 1), the data that counts (Part 2), and now the duties that follow a breach all in place, the series turns next to the standard the whole framework leans on — and the people who maintain it.

Operating a CEMS and unsure when the clock starts — or facing a notification you need to get right? Talk to us — we help operators and regulators apply the DOE CEMS Guidelines we helped write.

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This article is general guidance, not legal advice. For the precise legal position, refer to the Environmental Quality (Clean Air) Regulations 2014, the EQA 1974, and the DOE CEMS Guidelines.

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