Hazardous Locations and Special Occupancies

Introduction

This chapter covers the specific requirements of the Canadian Electrical Code (CE Code), Chapter V concerning locations where explosive or flammable atmospheres may exist, as well as special occupancies that impose additional safety rules. For the Red Seal exam, you must master the classification of locations, types of protection, ignition temperatures, and the specific rules for places like operating rooms, service stations, and swimming pools.

1. Classification of Hazardous Locations

1.1 General Principles

A hazardous location is a place where gases, vapours, flammable liquids, combustible dusts, or volatile fibres can create an explosive atmosphere. The classification determines the level of risk and the equipment permitted.

The CE Code divides hazardous locations into two main categories:

Class I: flammable gases and vapours

Class II: combustible dusts

Class III: volatile fibres and particulates

Each class is subdivided into divisions (1 or 2) according to the probability of the hazardous atmosphere being present.

1.2 Classes and Divisions

Class	Type of Substance	Division 1	Division 2
I	Gases, vapours, flammable liquids	Normal, continuous, or intermittent presence	Abnormal presence (leak, break)
II	Combustible dusts	Normal presence	Abnormal presence
III	Fibres and volatile particulates	Normal presence	Abnormal presence

Division 1: the hazardous atmosphere exists under normal operating conditions (e.g., inside a fuel tank).

Division 2: the hazardous atmosphere exists only under abnormal conditions (e.g., gas leak, failed ventilation).

1.3 Gas Groups (Class I)

Gases are classified into groups according to their explosion behaviour:

Group	Examples	Characteristic
A	Acetylene	Highly reactive
B	Hydrogen, manufactured gases	Highly flammable
C	Ethylene, ethylene oxide	Moderately flammable
D	Methane, propane, gasoline, alcohols	Less reactive (most common)

Important: The group determines the maximum allowable joint gap (flame path) for explosion-proof enclosures. Group A is the most restrictive.

1.4 Ignition Temperature and Temperature Classes

The ignition temperature is the minimum temperature at which a gas or vapour spontaneously ignites. Equipment is classified by temperature class (T-code) which indicates the maximum surface temperature of the equipment.

Temperature Class	Maximum Surface Temperature
T1	450 °C
T2	300 °C
T3	200 °C
T4	135 °C
T5	100 °C
T6	85 °C

Essential Rule: The maximum surface temperature of the equipment must be lower than the ignition temperature of the gas or vapour present. For dusts, the maximum surface temperature must not exceed 2/3 of the ignition temperature of the dust.

2. Equipment and Protection Methods

2.1 Types of Protection (Class I)

The CE Code recognizes several protection methods for equipment in hazardous locations:

Type of Protection	Symbol	Principle
Explosion-proof	Ex d	Enclosure resistant to internal explosion, joints cool the gases
Intrinsically safe	Ex i	Limited electrical energy (current, voltage, power)
Pressurized (purged)	Ex p	Air or inert gas maintained at positive pressure
Oil immersion	Ex o	Live parts immersed in oil
Sand filling	Ex q	Sand or fine powder surrounds live parts
Encapsulation	Ex m	Resin or compound encapsulates live parts
Increased safety	Ex e	Reinforced design (terminals, insulation)

2.2 Equipment Marking

Each certified piece of equipment must bear a nameplate indicating:

The class (I, II, III)

The division (1 or 2)

The group (A, B, C, D for Class I)

The temperature class (T1 to T6)

The type of protection (Ex d, Ex i, etc.)

Marking example: Class I, Division 1, Groups C and D, T3

2.3 Wiring and Connection

In a Class I, Division 1 location:

Rigid steel conduits (GRC) or aluminum conduits are mandatory

Seals must be installed within 450 mm of each enclosure

Seals must be filled with approved sealing compound

Threads must have at least 5 fully engaged threads

In a Class I, Division 2 location:

Rigid conduits or armoured cables (ACWU, Teck) are permitted

Seals are required only under certain conditions (e.g., change of zone)

Rule 18-152: Seals must be installed within 450 mm of the enclosure in Class I, Division 1 locations.

2.4 Equipment for Class II and III

For dusts (Class II):

Enclosures must be dust-tight (Type 9 or similar)

Surface temperatures must be verified to prevent ignition of dust deposits

Motors must be certified for Class II

For fibres (Class III):

Equipment must prevent the entry of fibres

Motors must be totally enclosed

3. Zones (International System)

The CE Code also permits the use of the zone system (0, 1, 2) for classifying Class I locations, as an alternative to divisions.

Zone	Definition	Division Equivalent
0	Explosive atmosphere present continuously or for long periods	Division 1 (extreme case)
1	Explosive atmosphere likely under normal conditions	Division 1
2	Explosive atmosphere unlikely under normal conditions, but possible under abnormal conditions	Division 2

Zone equipment is marked according to IEC 60079 standards with symbols such as Ex ia, Ex d, etc.

4. Special Occupancies

4.1 Operating Rooms and Treatment Rooms (Article 24)

Operating rooms are classified into three categories according to the level of explosion risk (presence of flammable anesthetics):

Category	Description	Requirements
Category 1	Flammable anesthetics used	All equipment must be explosion-proof
Category 2	Flammable anesthetics not used, but stored	Limited explosion-proof zones
Category 3	Non-flammable anesthetics only	Standard equipment with precautions

Rule 24-104: Receptacles in Category 1 rooms must be at least 1.5 m above the floor and 1.5 m from the head of the anesthesia apparatus.

Conductive floors are required in Category 1 and 2 rooms to dissipate static charges. Resistance must be between 25 kΩ and 1 MΩ.

4.2 Service Stations and Garages (Article 20)

Rule 20-102: Fuel dispensing areas are classified as follows:

Zone 1: inside tanks and piping

Zone 2: within a 450 mm radius of fill openings

Extended Zone 2: up to 1.8 m above the floor in the dispensing area

Electrical equipment in these zones must be certified for Class I, Division 1 or 2 locations according to the zone.

Rule 20-110: Emergency shut-off devices must be installed outside the building, at a minimum distance of 6 m from the dispensers.

4.3 Swimming Pools, Spas, and Fountains (Article 68)

Swimming pools are divided into zones according to horizontal and vertical distance from the water:

Zone	Definition	Requirements
Zone A	Within 1.5 m of the pool edge, up to 2.5 m above the water level	No electrical equipment except exceptions
Zone B	Between 1.5 m and 3 m from the edge	GFCI receptacles mandatory, 12 V max lighting
Zone C	Beyond 3 m	Standard equipment with GFCI protection

Rule 68-060: All receptacles within a 3 m radius of the pool must be protected by a Class A ground fault circuit interrupter (GFCI).

Rule 68-068: Submersible luminaires must operate at a maximum voltage of 12 V and be supplied by an isolating transformer.

4.4 Bathrooms and Saunas

Bathrooms:

Receptacles must be at least 1 m from the bathtub or shower

Receptacles must be GFCI-protected if within 3 m of water

Luminaires must be vapour-tight

Saunas:

Luminaires must withstand the ambient temperature (minimum 125 °C)

Receptacles are prohibited inside the sauna

The control thermostat must be installed outside

4.5 Elevators and Dumbwaiters (Article 62)

Elevators are governed by CSA B44 (Elevator Safety Code) in addition to the CE Code.

Main requirements:

Dedicated supply with accessible disconnecting means

Lighting for the hoistway and pit

Receptacle in the pit (GFCI-protected)

Cables and conduits compliant with movement requirements

Rule 62-110: The main elevator disconnecting means must be installed in sight of the controller or lockable.

5. Important Calculations and Verifications

5.1 Maximum Surface Temperature Calculation

To verify that equipment is acceptable:

T_max_surface < T_ignition_gas (with safety margin)

Example: For propane (ignition temperature = 493 °C), T3 equipment (200 °C) is acceptable.

5.2 Conductive Floor Resistance

The total resistance of the conductive floor must be:

Minimum: 25 kΩ (to prevent shock)

Maximum: 1 MΩ (to ensure static dissipation)

Measurement: between two 2.5 kg electrodes placed 1 m apart.

5.3 Conduit Seal Length

For Class I, Division 1 locations:

Seal required within 450 mm of each enclosure

Seal required at every passage through a wall or floor

The sealing compound must completely fill the seal

6. Canadian Electrical Code Rules (Key References)

Rule	Subject
18-002	Definitions of classes and divisions
18-052	Equipment marking
18-102	Wiring in Class I, Division 1
18-152	Conduit seals
18-202	Wiring in Class I, Division 2
20-102	Service station classification
20-110	Emergency shut-off
24-104	Receptacles in operating rooms
62-110	Elevator disconnecting means
68-060	GFCI receptacles around pools
68-068	Submersible luminaires

7. Installation and Verification Procedures

7.1 Installing a Conduit Seal

119.Install the seal on the conduit within 450 mm of the enclosure

120.Pull the conductors through the seal

121.Separate the conductors within the seal

122.Fill the seal with approved sealing compound

123.Allow the compound to cure before energizing

124.Verify the seal is tight (no visible gaps)

7.2 Verifying a Hazardous Location

126.Identify the class, division, and group

127.Verify the ignition temperature of the substances present

128.Select equipment with the correct T-code

129.Verify the equipment markings

130.Inspect seals and sealing fittings

131.Measure conductive floor resistance (if applicable)

8. Common Pitfalls to Avoid

134.Confusing Division 1 and Division 2: Division 1 is for normal presence, Division 2 is for abnormal presence. Always re-read the definitions.

135.Ignoring the ignition temperature: T6 equipment (85 °C) is always acceptable, but T1 (450 °C) may be too hot for certain gases. Always check the T-code.

136.Forgetting conduit seals: In Class I, Division 1 locations, seals are mandatory within 450 mm of each enclosure. Many candidates forget this distance.

137.Using non-armoured cables in Division 1: Only rigid conduits are permitted in Class I, Division 1. Armoured cables are for Division 2.

138.Confusing pool zones: Zone A is the most restrictive (1.5 m), Zone C is the least restrictive (beyond 3 m). GFCI receptacles are required up to 3 m.

139.Forgetting conductive floor resistance: The values are 25 kΩ minimum and 1 MΩ maximum. Many candidates reverse these values.

140.Neglecting the gas group: Group D is the most common (methane, propane), but Group A (acetylene) is the most restrictive. Equipment certified for a higher group (A) can be used for a lower group (D), but not the reverse.

141.Ignoring marking requirements: Equipment without a complete nameplate is non-compliant. Always check the class, division, group, and T-code.

9. Exam Tips

Memorize the classification tables: Classes, divisions, groups, T-codes. These tables are frequently tested.

Learn the key distances: 450 mm (seals), 1.5 m (pools), 3 m (GFCI), 6 m (emergency shut-off).

Understand the protection logic: The higher the risk, the stricter the protection. If you don't know, choose the most restrictive option.

Practice temperature calculations: Always verify that the surface temperature is lower than the ignition temperature.

Re-read the definitions: Trick questions often focus on the distinction between Division 1 and Division 2, or between Class I and Class II.

Summary

Hazardous locations are classified as Class I (gases), Class II (dusts), and Class III (fibres).

Each class is divided into Division 1 (normal presence) and Division 2 (abnormal presence).

Gases are grouped into A, B, C, D according to their reactivity.

Equipment carries a T-code (T1 to T6) indicating the maximum surface temperature.

Protection methods include explosion-proof (Ex d), intrinsically safe (Ex i), pressurized (Ex p), etc.

In Class I, Division 1, rigid conduits are mandatory with seals within 450 mm of enclosures.

Operating rooms are classified into categories 1, 2, and 3 according to the use of flammable anesthetics.

Service stations have classified zones with specific distance requirements.

Swimming pools are divided into zones A, B, C with GFCI protection requirements up to 3 m.

Elevators are governed by CSA B44 and the CE Code, with a dedicated disconnecting means.

Conductive floors must have a resistance between 25 kΩ and 1 MΩ.

Common Pitfalls (Recap)

Pitfall	Correction
Confusing Division 1 and 2	Division 1 = normal presence, Division 2 = abnormal condition
Forgetting the seal distance	450 mm maximum from the enclosure
Using cables in Division 1	Rigid conduits mandatory
Reversing conductive floor values	25 kΩ min, 1 MΩ max
Ignoring the T-code	Always verify T_max < T_ignition
Confusing gas groups	A = acetylene (most restrictive), D = methane/propane (common)
Forgetting pool zones	GFCI required up to 3 m, Zone A = 1.5 m
Neglecting marking	Check class, division, group, T-code

This chapter covers the essential knowledge required for the Red Seal exam in construction electricity regarding hazardous locations and special occupancies. Review the CE Code rules mentioned and practice with sample questions to reinforce your understanding. Good luck with your preparation!

Hazardous Locations and Special Occupancies