Environmental Science & Engineering Magazine24 | March 2013

Wastewater Treatment

tion in which “explosive gas atmospheresare likely to occur in normal operation, orthe location is adjacent to a Class I, Zone0 location.” Zone 2 is a location in which“explosive gas atmospheres are not likelyto occur in normal operation, or the loca-tion is adjacent to a Class I, Zone 1 loca-tion, unless adequate continuous positivepressure ventilation is provided.” Basedon these definitions, a wet well is consid-ered Class I, Zone 1 and a dry well is con-

In Ontario, standards for the instal-lation and maintenance of electricalequipment are established by theOntario Electrical Safety Code

(OESC). In the past, it did not containspecific rules regarding electrical instal-lations in sewage pumping stations (SPS)or treatment plants. Typically, a processengineer would identify hazards within asewage facility and the electrical engi-neer would design in accordance with theappropriate rules in the OESC.

However, in 2009 the OESC was up-dated with specific rules applicable tosewage treatment facilities. The new in-formation in Section 22, when read inconjunction with Section 18 – HazardousLocations, provides detailed rules to beused by a qualified person to establishhazardous area classifications for typicalspaces within a sewage facility, such as awet or dry well.

Class I hazardous locations are de-fined as “locations in which flammablegases or vapours may be present in the airin quantities sufficient to produce explo-sive gas atmospheres.”

Class I hazardous areas are subdi-vided into zones, according to the fre-quency and duration of an explosive gasatmosphere. Zone 1 is defined as a loca-

sidered Class I, Zone 2.All new electrical installations, in ei-

ther a new facility or a facility that isbeing upgraded, must comply with thelatest edition of the OESC. The new rulesin Section 22 present a unique challengefor the upgrade of older sewage pumpingstations, many of which were designedwithout specific guidelines for hazardousarea classifications.

Case study: Victoria Avenue SewagePumping Station

Originally constructed in 1979, the Vic-toria Avenue Sewage Pumping Station(SPS) is a dry/wet-well style facility lo-cated in the Town of Lincoln, in the Niag-ara Region. It is equipped with two 50-hpconventional close-coupled centrifugalpump units. One duty and one standby. Theexisting station rated capacity is 79.5 L/s.

In 2011, R.V. Anderson AssociatesLtd. was retained to design an upgrade tothe existing facility. This included replace-ment of the existing pump units with newdry-pit submersible units selected to in-crease the station rated capacity to 120L/s. Other works included replacement ofthe existing standby diesel generator, re-placement of aging building electrical andmechanical systems, and upgrades to theelectrical and control systems to accom-modate the new larger pump units.

The existing Victoria Avenue SPS electrical room, with pump removal openingsand a stair well leading to the dry well below.

Victoria Avenue SPS main floor plans: A) existing layout with interconnectedgenerator room, electrical room and dry well; B) proposed layout, with newelectrical room physically separated from dry well.

The impact of hazardous area classifications onsewage pumping station upgrades By Doug Pease

ES&E Mar2013_3_2012 13-03-27 8:06 PM Page 24

March 2013 | 25www.esemag.com

Wastewater Treatment

At Victoria Avenue SPS, the electricalroom is located at grade and is intercon-nected to the dry-well space below by anopen stairwell and several pump removalopenings. The generator room is also lo-cated at grade, and is connected to theelectrical room by an interior door.

The OESC uses the term suitably cutoff to describe “an area rendered imper-meable and cut off from an adjoining areawith no means of liquid, gas or vapourcommunication between areas at atmos-pheric pressure.” By this definition, theelectrical and generator rooms are not suit-ably cut off from the dry well, so they mustbe considered Class I, Zone 2 locations.

Classification of the electrical andgenerator rooms presented a major de-sign challenge, because none of the ex-isting equipment installed in these spacesis suitable for installation in a hazardousarea. Four possible options were consid-ered to address this issue.

The first option required replacementof all electrical equipment located in thedry well, electrical room and generatorroom with new equipment suitable for in-stallation in a Class I, Zone 2 hazardousarea. Typically, equipment with this ratingis much more expensive than the non-classified equivalent. However, somepieces of equipment such as the standbydiesel generator are not available with aClass I hazardous area rating and, there-fore, would need to be located elsewhere,in a non-classified area.

The second option involved changingthe room classifications to “unclassi-fied”, by providing continuous positivepressure ventilation at a rate of six airchanges per hour (ACPH). This ventila-tion rate would be required in the electri-cal room, mechanical room and dry well.Should the ventilation system becomeunavailable due to maintenance or failure,these areas would revert to Class I, Zone2. Any electrical equipment not suitablefor installation in such a hazardous areawould have to be de-energized.

Although the new dry-pit submersiblepump units would be rated to operate inthe Class I, Zone 2 condition, the pumpcontrol equipment located in the electri-cal room would have to be de-energized.This would effectively take the station of-fline in the event of a failure in the venti-lation system. To avoid this scenario, itwould be possible to install a backup ven-

tilation system capable of providing therequired positive pressure ventilation,when the primary system is unavailable.

The third option was to construct anew building to house the electrical andcontrol equipment, as well as the standbygenerator. The new building would be anelectrically unclassified area by virtue ofphysical separation from both the existingdry-well and wet-well spaces. The build-ing electrical systems, such as lighting,required in the existing dry well, electri-

cal room and generator room would bereplaced with new equipment suitable forClass I, Zone 2.

This option was considered quite ex-pensive due to the new structure. Addi-tionally, it would be challenging toaccommodate a suitably sized building,within the extremely limited property, ofthe existing station.

The fourth option involved convertingthe existing generator room, janitor room

continued overleaf...

ES&E Mar2013_3_2012 13-03-27 8:06 PM Page 25

Environmental Science & Engineering Magazine26 | March 2013

Wastewater Treatment

sidered low-maintenance because itavoids the need for a complicated backupventilation arrangement. Finally, it wasfound to be quite cost-effective becauseit required only minor architectural mod-ifications, and the equipment in the newelectrical room did not require any haz-ardous area ratings.

The dry-well space and pump removalroom (existing electrical room) will re-main Class I, Zone 2 locations. All elec-trical equipment in these spaces,including the pump removal system,lighting and other building electrical sys-tems, will be replaced with new equip-ment suitable for installation in ahazardous area.

Additionally, it was recognized thatcertain activities such as the use of powertools present a potential hazard when un-dertaken within an electrically classifiedarea. To mitigate these potential risks, anew ventilation system was designed forthe dry well and pump removal room.Under normal conditions, this system willprovide positive pressure ventilation at arate of three ACPH. However, at the pushof a button the ventilation rate can be in-

and washroom into a new electrical room.This new space would be physically sep-arated from the existing electrical room(now a dedicated pump removal room),by replacing the interconnecting interiordoor with a new wall. As a result, the newelectrical room would be electrically un-classified, so equipment installed withinit would require no special ratings.

However, this option would require therelocation of the standby generator to anew building or an exterior, weather-proof, sound-attenuating enclosure.

After review of these four options, itwas ultimately decided to proceed withoption four, which was to create a newunclassified electrical room within theexisting facility. This was found to haveseveral key advantages that made it a par-ticularly attractive solution.

Most importantly, the new electricalroom will remain an unclassified locationregardless of the operation of the buildingventilation systems. As such, there willnot be a situation in which the electricalsystems may have to be de-energized,stopping pump operation.

Additionally, this alternative was con-

creased to six ACPH, temporarily declas-sifying these spaces.

SummaryThe rules in Section 22 of the OESC

present a challenge for wastewater utilityproviders across Ontario. Many oldersewage pumping stations, in particulardry/wet-well style facilities, have com-mon spaces that contain process pumpingand piping, electrical equipment andstandby generators. When these stationsundergo electrical upgrades, the electricalclassification of these spaces must beconsidered.

As demonstrated by the Victoria Av-enue SPS project, there are many possiblesolutions to satisfy the requirements ofthe Ontario Electrical Safety Code. Themost suitable alternative will depend ona number of factors, including layout ofthe existing facility, and the scope andbudget of the proposed upgrade.

Doug Pease is with R.V. Anderson Associates Ltd.

E-mail: dpease@rvanderson.com

E. terratecsales@amwater.com W. www.terratec.amwater.com

NASM Plan Consulting and Applicationof Industrial and Municipal Materials

Serving municipal, industrial and commercialNASM generators across the province

Services Include:· Preparing Non-Agricultural Source Material (NASM) Plans for submission to OMAFRA

· Provide all preparation for NASM Plans including soil sampling, field assessments and GIS site maps in compliance with OMAFRA and MOE regulations

· Perform follow up documentation for single and multi year NASM plans

· Provide transport and injection application of liquid and solid NASMs

For more information please contact:Rob Alton          or Mark JaniecPAg, CCA-CA PAg, CCA-CA905-312-4095 905-878-2800 ext 223

ES&E Mar2013_3_2012 13-03-27 8:06 PM Page 26