Designing an RECD Installation in a Flood-Prone Plant Room

Some plant rooms carry a quiet clue on the wall: a faint brown tide mark at knee height, or a line someone painted after the last bad monsoon with a date written beside it. That line is the most important dimension in the room. It tells you how high the water has come before, and it should decide where a retrofit emission control device, its controls and its connections go.

Flooding is not only a coastal problem. Basements in city centres fill during cloudbursts, low-lying industrial estates collect runoff from roads, and ground-floor generator rooms near drains back up when the drains do. Urban flooding has become common enough in India that the National Disaster Management Authority publishes specific guidelines on flood and urban flood management. For an RECD, a flood brings particular risks: water inside the filter, mud in the exhaust, drowned sensors and a generator that may need to run as soon as the water drops.

This article sets out a way to design an RECD installation for a plant room that may flood, built around three lines of defence and a recovery plan.

Start With a Number: The Design Water Level

Every flood design decision depends on one number: how high the water could reach in this room. Call it the design water level.

Where to find it

• Site history. Ask long-serving staff, look for tide marks, check maintenance logs and insurance claims
• Local authority information. Municipal flood maps or drainage studies, where available
• Building drawings. The finished floor level of the plant room compared with surrounding ground, road and drain levels
• Neighbouring buildings. How high water reached in comparable basements nearby
• The building’s own risk assessment, if one was done for insurance or disaster planning

Add a margin

Floods recorded in living memory are not the worst floods possible. Add a margin above the highest recorded level. The size of the margin is a judgement for the owner and their consultant, balancing cost against the consequences of being wrong.

Write it down

Mark the design water level on every drawing and paint it on the plant room wall. Everything below the line is assumed to get wet. Everything that must survive is placed above it.

Why an RECD Is Vulnerable to Flooding

Before looking at defences, it helps to understand what water does to an RECD.

Part	What flood water does	Consequence
Filter substrate	Soaks the ceramic structure; mud and silt enter the channels	Blocked channels; possible cracking when heated while wet
Catalyst coating	Contaminated by salts, mud and oil carried in flood water	Reduced activity
Housing and cones	Corrosion from prolonged wetting	Shorter life; leaks
Insulation	Becomes waterlogged	Loses insulating value; causes corrosion underneath
Sensors and wiring	Short circuits; corrosion of connectors	False readings or no readings
Control box or display	Electronics damaged	Loss of monitoring
Supports and anchors	Corrosion; washout of base material	Weakened supports

There is also a risk from the engine side. If water enters the engine’s air intake or exhaust while it is stopped, or the engine is started with water in it, serious damage can follow. Engine flood recovery is outside the scope of this article, but the RECD plan must fit within the wider generator flood plan.

The filter’s structure, and why water and debris matter to it, is explained in our guide on what an RECD is and how it works.

The Three Lines of Defence

Good flood design uses three overlapping layers.

1. Keep water out of the room where practical
2. Keep critical parts above the design water level if water gets in
3. Stop water entering the exhaust system through its openings and drains

Each layer reduces the load on the next. None is perfect on its own.

Line One: Keep Water Out of the Room

The cheapest flood is the one that never enters the plant room. These measures belong to the building, but the RECD project is often a good moment to review them.

Entrances and thresholds

• Raised thresholds or ramps at doors
• Removable flood barriers that can be fitted to door frames when heavy rain is forecast
• Doors that open outward and seal against pressure, where the design allows

Ventilation openings

Generator rooms need large air openings for cooling and combustion. Low-level louvres are a common flood entry point. Where possible:

• Raise air inlets above the design water level
• Fit flood shutters to unavoidable low openings, with a procedure for closing them
• Remember that closed openings cannot ventilate a running engine; the plan must say who opens them and when

Drains and cable entries

• Floor drains can let water in rather than out when the external drain backs up. A check valve or backflow preventer on the drain outlet helps.
• Cable and pipe entries below ground need sealing systems rated for water pressure
• Fuel line ducts from external tanks are another path

Pumping

A sump pump in a pit at the lowest point removes water that does get in. For it to help during a flood, it needs:

• Power from a source that will be available, which may be the generator itself
• A discharge route that will not simply flow back
• A level alarm
• Regular testing

Basement plant rooms face these issues most acutely; our guide on RECD installation in basement DG rooms covers space and access there.

Line Two: Keep Critical Parts Above the Water

If water enters, the second line keeps essential equipment above it.

Raise the device

The simplest and most effective measure is to mount the RECD with its lowest point above the design water level. Options include:

• A taller floor frame or concrete plinth under the device
• Wall mounting on a suitable wall, at a height above the water line
• Moving the device up the exhaust route, for example to the base of a riser or an upper level

Raising the device changes its support design, pipe routing and service access. Our guide on horizontal vs vertical RECD mounting explains how orientation can help gain height, and the rooftop RECD installation guide covers devices placed well above ground.

Raise the controls

Sensors, displays, control boxes and junction boxes should sit above the design water level, with cable routes that rise to them rather than dipping below.

Raise the engine, if possible

Many flood-prone sites raise the whole generator on a plinth. If the engine sits below the water line, the RECD’s elevation buys less, because the generator cannot run until it is cleaned and checked anyway. Where a plinth is being considered, the RECD should be designed for the final engine height.

What may stay low

Some items can accept wetting if they are designed for it and inspected afterwards: concrete plinths, galvanised or stainless support legs, sealed conduit and drain lines. The plan should list them explicitly so nobody assumes everything low is a problem.

Line Three: Stop Water Entering the Exhaust

Even with the device above the water line, the exhaust system has openings that can let water in.

The engine end

If water reaches the engine’s exhaust outlet height, it can flow backwards through the turbocharger into the engine, or forward along the pipe towards the device. Raising the engine is the main protection here.

Low points and drains

Exhaust systems often have condensate drains at low points. If those drains are below the design water level and open, flood water can enter through them. Options include:

• Drain valves that are kept closed except when draining
• Drain lines extended upward and terminated above the design water level
• Non-return fittings on drain outlets

The outlet

The stack outlet is usually high and safe from flood water, but heavy rain during a flood event can enter through an uncapped outlet. A rain cap or angled outlet is cheap insurance. Our companion guide on protecting RECDs against rainwater and condensation covers this in detail.

Wall penetrations below the water line

If the exhaust leaves the room through a wall below the design water level, the penetration must be sealed against water pressure from outside, as well as allowing for thermal movement.

Choosing a Layout: Four Options Compared

Layout option	How it handles flooding	Trade-offs
Device on a raised frame in the plant room	Device above water; pipe below may get wet	Tall frame needs bracing; service needs a platform
Device wall-mounted high in the plant room	Device well above water	Wall must be suitable; access by ladder or platform
Device at the base of the riser, on an upper level	Device well clear of flood water	Longer pipe before device; cooler exhaust; access through another floor
Device on the roof or at stack top	Completely clear of flood water	Coolest exhaust; lifting and access harder; structural checks

There is no single best answer. Sites that run frequently at good load may be fine with a higher, cooler position. Lightly loaded standby sets need the device closer to the engine and may need insulation to keep regeneration working. Our guide on choosing an RECD for a generator running at low load explains why temperature matters.

Electrical and Monitoring Details

Flooding is an electrical problem as much as a mechanical one.

• Cable routes should rise from the device to panels, never dip into the floor zone
• Junction boxes should be above the design water level or rated for submersion
• Connectors on sensors should have suitable ingress protection
• Remote monitoring helps the facility team see the device’s state during and after a flood without entering a wet room
• Isolation of the device’s controls should be possible from outside the flood zone

The generator’s own electrical system, batteries and starting circuits face similar risks. Our troubleshooting articles on common reasons a generator won’t start and why a generator battery is not charging are useful during recovery.

The Flood Operating Procedure

Design is half the job. The other half is what people do when water arrives. The RECD plan should feed into a short, written procedure.

Before the monsoon

• Test the sump pump and level alarm
• Check drain non-return valves and closures
• Confirm flood barriers and shutters are on site and complete
• Check that the stack rain cap is in place
• Inspect insulation cladding and seals on the RECD and pipe
• Brief the team on the procedure

When heavy rain is forecast

• Fit door barriers
• Close low-level drain valves on the exhaust
• Make sure the sump pump has power
• Check that ventilation needed for any expected generator run will still be available

During a flood

• Do not start the generator if water has reached the engine or its intake or exhaust openings
• If water stays below the design level and the generator is needed, run it according to the site plan, with ventilation open
• Monitor water level and the device’s readings remotely where possible
• Keep people out of flooded electrical areas

After the water recedes

Follow the recovery checklist below before returning the generator and RECD to service.

The Post-Flood Recovery Checklist

Step	What to do	Why
1	Record the maximum water level reached, with photographs	Compare with the design level; update the plan
2	Make the room electrically safe before entry	Prevent shock
3	Inspect the engine according to the engine maker’s flood guidance	Water in the engine causes serious damage if started
4	Check whether water reached the RECD, its drains or its connections	Decide whether the device needs inspection
5	Open drains and check for water in the exhaust	Water in the pipe will be blown into the filter
6	If water reached the device, contact the vendor before running	The filter may need inspection, drying or cleaning
7	Inspect sensors, cables and junction boxes	Replace damaged parts
8	Remove and replace wet insulation	Prevent hidden corrosion
9	Inspect supports and anchors	Look for washout and corrosion
10	Run the set at light load first, then build up, watching backpressure	Detect blockages early
11	Record everything in the maintenance log	Support future decisions and insurance claims

Never run hot exhaust through a filter that may be soaked without the vendor’s advice. Rapid heating of a wet ceramic substrate can damage it. Our RECD maintenance guide and the monthly maintenance checklist for diesel generators both include checks that should be repeated after a flood.

Fuel, Oil and Contamination

Flood water rarely stays clean. It picks up sewage, oil, fuel, silt and debris. Two consequences matter for an RECD:

• Contaminated deposits inside the exhaust or device may include salts and oil that affect the catalyst. The vendor should advise on cleaning.
• Fuel contamination with water is common after floods if tanks or vents were submerged. Running on contaminated fuel causes poor combustion and smoke, which loads the filter quickly. Check fuel and filters before running; our generator fuel filter replacement guide explains the process.

Fuel and oil releases in flood water also raise environmental questions. Keep records of any spills and their handling alongside your environmental compliance records.

A Walkthrough: Hospital Service Block in Mumbai

This is an illustrative case.

The site

• A 1250 kVA set in a lower-ground plant room of a hospital service block
• The plant room floor sat about 1.2 m below the adjacent road
• During a heavy monsoon three years earlier, water had reached about 450 mm above the plant room floor before the pumps caught up
• The exhaust left the canopy at about 1.6 m, ran across the room and rose through a shaft to the terrace

The design water level

Based on the tide mark, staff accounts and the road level, the hospital’s consultant set a design water level of 900 mm above the plant room floor, giving a margin over the recorded flood.

The decisions

Line one. Demountable flood barriers were added to both doors. The floor drain received a non-return valve. A second sump pump was installed, with power from the generator’s essential board and a level alarm to the building management system. Two low air inlet louvres were fitted with flood shutters; a procedure assigned the duty engineer to close them when rain was forecast and reopen them before any generator run.

Line two. The generator was already on a 300 mm plinth, with its exhaust outlet well above the design level. The RECD was placed on a raised steel frame so its lowest point sat about 1.4 m above the floor, comfortably above the design level. A small platform with a handrail was added for service. All sensors, the display and junction boxes went above 1.5 m, with cables rising from the device.

Line three. The exhaust condensate drain, previously a short open pipe near floor level, was extended upward and fitted with a valve above the design level. The terrace outlet got a rain cap.

Procedure. A one-page flood procedure was laminated and fixed inside the plant room door, with a matching section in the hospital’s disaster plan.

The test

The following monsoon brought a heavy rain event. Water entered to about 200 mm before the pumps cleared it. The generator ran during a grid outage that night with the flood shutters open, since water stayed well below the shutters. The RECD never saw water, and post-event checks found only damp insulation at the base of the frame legs, which was replaced.

Hospitals combine flood risk with the highest stakes for backup power; our guide on RECDs for hospitals covers retrofit planning around critical loads. The 1250 kVA DG set RECD page covers the rating used here.

Sites With Other Water Risks

Coastal sites

Storm surges carry salt water, which is more corrosive than rainwater. Stainless supports, sealed connectors and thorough rinsing after any flood are important. Our guide on choosing an RECD for coastal salt-laden environments explains material choices.

Water and wastewater plants

These sites often sit at low points by design. Humidity and occasional flooding combine; see our guide on RECDs for water treatment plants.

Remote and unattended sites

Telecom shelters and pumping stations may flood with nobody present. Remote monitoring of water level, generator status and device readings becomes essential. Our guide on RECDs for telecom sites discusses unattended operation.

Questions for the Vendor and Consultant

1. What design water level are we using, and how was it set?
2. Where will the device’s lowest point sit relative to that level?
3. Where are the drains, and how are they protected against flood water entering?
4. Where are sensors, cables and control boxes, and what ingress rating do they have?
5. If water reaches the device, what is your inspection and recovery procedure?
6. Does raising the device affect exhaust temperature or backpressure, and by how much?
7. How will technicians reach the device for service at its raised position?

Compliance Note

The device itself is approved under CPCB’s System and Procedure for Emission Compliance Testing of RECDs. Flood design is a site matter, but a device that has been flooded and not properly inspected may perform poorly and draw attention during inspection. Keep the design water level, procedures and post-flood records with your installation file. Our article on what happens during a pollution control board inspection explains what inspectors look at.

Frequently Asked Questions

Can an RECD survive a flood?

It depends on whether water reached it and what the water contained. A device kept above the water line is unaffected. A device that was submerged needs inspection by the vendor before use and may need cleaning, drying or parts replacement.

How high should an RECD be mounted in a flood-prone room?

Its lowest point, and all its sensors and controls, should be above the design water level set for the room, which is the highest expected flood plus a margin.

Should I run the generator during a flood?

Only if water has stayed well below the engine and its openings, the room is electrically safe and ventilation is available. Follow the engine maker’s guidance and your site procedure.

What if the exhaust drain is below the flood level?

Extend the drain line upward with a valve above the design level, keep it closed except when draining, or fit a non-return fitting.

Is it better to move the RECD to the roof?

It removes flood risk but brings cooler exhaust, harder access and structural questions. It suits some sites well and others poorly.

Draw the Line, Then Design Above It

A flood-prone plant room does not rule out an RECD. It changes the order of decisions. Set the design water level first, mark it everywhere, and design every part of the installation in relation to it: keep water out where you can, keep the device and its controls above the line, close the exhaust’s low openings and write down exactly what people should do before, during and after a flood. Then, when the water does come, the generator can do its job as soon as it is safe to run.

Aceget designs RECD installations for basements, low-lying plant rooms and coastal sites, including raised frames, protected drains and post-flood recovery procedures. To plan an installation in a flood-prone room, get in touch with Aceget, or explore the retrofit emission control device range.