Chemical Feeder Interlock: Monthly Challenge Test and Records

Once a month, unless the manufacturer specifies otherwise, under MAHC 5.7.3.5.1.4.1.1 (check what your state adopted). You turn off recirculation pump flow to the feeder, confirm the feeder shuts off through the electrical interlock, and restart flow immediately (5.7.3.5.1.4.1.2). The test date goes on the daily record (6.4.1.6 item 7). Follow the manufacturer's procedure, the label and SDS, and call 911 for a suspected release.

Why is this a safety test and not paperwork?

The Annex (4.7.3.2.1) explains the failure mode. If recirculation stops while the acid and chlorine feed pumps keep running, concentrated acid and chlorine can build up in the lines and form chlorine gas. The gas can reach the venue when the pump restarts, or the pump room if a line is open. The Annex cites CDC surveillance and a 2017 MMWR report on inhalational chlorine injuries at public aquatic venues in California for 2008 to 2015.

CDC's chemical safety page says the same in design terms: alarm on pump shutdown, and a device that deactivates the chlorine and pH feed pumps on no or low flow. The test proves that device still works. Annex 4.9.2 gives wider context: of 32 pool chemical health events reported to CDC by Maryland and Michigan in 2007 to 2008, 26 (81.3%) could be at least partly attributed to chemical handling errors such as mixing incompatible chemicals.

What does the code require around the interlock?

• Interlock design (4.7.3.2.1.3). An electrical interlock made of at least two of: a recirculation pump power monitor, a flow meter, switch or pressure switch in the return line, or a flow device at the controller. Installed per the manufacturer and never altered (4.7.3.2.1.3.1). New or replacement equipment must show a visual alarm or other indication to alert staff to evacuate bathers (4.7.3.2.1.3.2).
• Feeders (5.7.3.5.1.2, 5.7.3.5.1.3). Installed and interlocked so the feeder cannot run in low or no flow, with fail-proof features so chemicals cannot feed into the venue, other piping, the source water supply or the deck area.
• Controllers (5.7.3.7). An automated controller, interlocked per 4.7.3.2.1.3, with its probe sample line upstream of all treatment injection points (5.7.3.7.2), checked in person at the start of the operating day (5.7.3.7.3).
• Daily (5.7.3.5.7). Chemical tubing, connections, supports and double containment piping checked daily for leaks.
• Annex 5.7.3.5.1.2. Periodic visual inspection to see whether the interlock still looks installed per the manufacturer and unaltered.

How do you run the challenge test?

The MAHC gives the core of the test in one sentence. The steps around it come from the same code and CDC; where your manufacturer's procedure differs, use theirs.

1. Close the venue to bathers first. 5.7.3.5.1.2.1 says that when the pump is stopped manually "for any reason and duration," all bathers are evacuated until the responsible supervisor or qualified operator has evaluated the cause. CDC says to close the venue before servicing the feed or recirculation systems. A test that stops the pump falls under that rule, and we close for any version of the test.
2. Have the right person and gear. A trained person, the manufacturer's test instructions, PPE per the label and SDS. Do not improvise on equipment you have not been trained on.
3. Note the time and the devices. Which of the interlock devices (power monitor, return-line switch, controller flow device) the test exercises, as 4.7.3.2.1.3 requires at least two.
4. Turn off recirculation flow to the feeder as the manufacturer directs. Keep flow off only long enough to see whether the feeder stops.
5. Confirm triggered shutoff. The feeder stops through the electrical interlock. If your equipment is new or replaced, also confirm the visual alarm or indication (4.7.3.2.1.3.2).
6. Restart recirculation flow immediately after confirming shutoff (5.7.3.5.1.4.1.2). If the feeder did not stop, do not run this step on your own: go to the failed-test row in the table below.
7. Hold bathers out for 5 minutes after restart. The MAHC's 5-minute wait is written for a real alarm (5.7.3.5.1.2.2). CDC says not to let swimmers back until the feed and recirculation systems have run for at least 5 minutes, if water quality meets required standards. Confirm your reopening reading before you open.
8. Log it (below) and sign it.

If anything seems wrong during the test, such as an odor, irritation or a leak, or you are not sure what you are seeing, get everyone out of the area, keep them out, and call 911, then follow your release plan. See our chemical release response post.

What happens when the interlock fails or trips?

What you see	What to do	Basis
Feeder stops, alarm shows	Restart flow, hold 5 minutes, log a pass	5.7.3.5.1.4.1.2, CDC
Feeder keeps running with flow off	Stop the feeders by hand as the manufacturer directs (CDC: feed and recirculation both off before servicing). Keep the venue closed; the qualified operator decides how flow is restored, because a restart can carry chlorine gas into the venue (Annex 4.7.3.2.1). Any odor or irritation: everyone out, call 911. Call service, log the malfunction	6.6.3.1 item 9, 6.6.3.2, 6.4.1.6 item 6, CDC
Interlock disabled or bypassed	Imminent health hazard: close	6.6.3.1 item 9, 6.6.3.2
No visual alarm on new or replacement equipment	Ask the manufacturer and your health department	4.7.3.2.1.3.2
Interlock trips in service	Evacuate all bathers; no re-entry until the cause is understood, the interlock is manually overridden for restart, and 5 minutes have passed since restart	5.7.3.5.1.2.1, .2

After a fail, retest after the repair and log both the failure and the retest with dates and times. A placarded venue stays closed until the hazard is corrected (6.6.4.1). UV and ozone interlock trips are evaluated as possible low flow with the same evacuation and re-entry steps (5.7.3.2.1.1.1, 5.7.3.2.2.6).

What does the record look like?

6.4.1.6 item 7 requires the dates of challenge testing, and item 6 maintenance and malfunctions with dates and times. Keep records for at least 3 years (6.4.1.2.1). Suggested fields:

Field	Example entry
Pool, date, start time	Pool 14, 12 May, 06:10
Tester and certificate	Operator A, certificate on file
Procedure used	Manufacturer's sheet, rev. 3
Devices exercised	Return-line flow switch, controller flow device
Feeder stopped? Alarm?	Yes, yes
Flow restored, 5-minute hold ended	06:19, 06:24
Reopening FC and pH	Entered from the opening test
Signed, next due	Initials, by 12 Jun (31-day rule)

A failed test gets a second row: failure, work order, repair date, retest result, who closed the venue and when.

How do you cover 30 pools?

Split the pools into four buckets of 7 or 8, one per week, so the month has built-in room for repeats. Put the fifth week on catch-ups only. Name one owner per bucket and a second person who reviews the logs.

Decide your missed-test rule in writing. "Once monthly" can mean one test in each calendar month, or no more than 31 days between tests. Say tests are on 3 March and 28 April. That is one per month, but 56 days apart. The stricter rule catches this.

To see misses in logs, pull item 7 for every pool and sort by last test date. A pool with no date in the month, or more than 31 days since the last, is a miss. Two failures in a row at one pool point to an equipment problem, so escalate it to service and your area manager. If you track scheduled work in Poolean, the monthly test can sit there as scheduled work, and you can see what is overdue at each pool.

Under OSHA's Hazard Communication standard (29 CFR 1910.1200), your written program must list the hazardous chemicals on site (e), SDSs must be readily accessible each shift (g)(8), and training happens at initial assignment and when a new hazard is introduced (h)(1). OSHA's hazcom page covers the labels and SDS formats. MAHC 6.0.1 adds chemical training before anyone accesses chemicals, with an annual review, so feeder work should be limited to people who have it.

For the monthly rhythm, see preventive maintenance, the daily opening checklist and inspection preparation. To set this up across your pools, book a 30-minute call.

The short version

• Test the feeder interlock monthly unless the manufacturer says otherwise: flow off to the feeder, confirm shutoff, restart immediately.
• Keep bathers out during the test and for 5 minutes after restart; follow the label, SDS, your training and your health department.
• Log the date (6.4.1.6 item 7) and any malfunction (item 6).
• A missing, non-working, disabled or bypassed interlock is an imminent health hazard that requires closing.
• Write down your missed-test rule and check dates across all pools every month.