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Home › Publications › OHS Regulation › Guidelines Part 9

Guidelines Part 9

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Guidelines Part 9 - Lockout and isolation

G9.18 Isolation of confined spaces

Issued April 9, 2008

Regulatory excerpt
Section 9.18 (Isolation) of the OHS Regulation ("Regulation") states:

(1) Except as provided in subsection (2), before a worker enters a confined space, adjacent piping which contains or has contained a harmful substance must be controlled by
(a) disconnecting, blanking or blinding, or equivalent engineered system, or
(b) if the adjacent piping contains a harmful substance that is not a gas or a vapour, nor a liquid of sufficient volatility to produce a hazardous concentration of an air contaminant in the discharge of the piping, a double block and bleed system.

(2) If adjacent piping contains or has contained a substance that is hazardous only because of its pressure, temperature or quantity, before a worker enters the space, the pressure must be controlled
(a) to meet the requirements of subsection (1),
(b) provided there is no other pressure source or head pressure, by de-energizing and locking out the pressure source and depressurizing the line, or
(c) by other effective means.

(3) Repealed [B.C. Reg. 243/2006, effective January 1, 2007.]

(4) Except when used in an acceptable double block and bleed system, the closing of one or more valves in a line is not an acceptable means of isolation.

(5) Isolation of a confined space from gases found in a gravity-flow municipal or domestic sanitary or storm sewer system may be accomplished by a p-trap, provided that
(a) the integrity of the trap is ensured immediately upon entry, and
(b) the atmosphere is continuously monitored and shown to contain clean respirable air.

Purpose of guideline
Section 9.18 of the Regulation addresses the isolation of confined spaces from hazardous substances in adjacent piping. Isolation is intended to address hazards arising from fluids (typically liquids, vapours, and gases) and other flowable materials such as slurries, dust, and powders.

The purpose of this guideline is to clarify when section 9.18 applies, and to provide interpretive information for each of its subsections.

Adjacent piping
The definition of adjacent piping in section 9.1 of the Regulation is

"adjacent piping" means a device such as a pipe, line, duct or conduit which is connected to a confined space or is so located as to allow a substance from within the device to enter the confined space;

Under this definition there are two general types of adjacent piping.

• Piping that is "connected to a confined space," which is piping that has openings in the space creating the possibility of emptying its contents into the confined space.
• Piping that is not physically connected to the confined space but may be located nearby in a manner that could allow a substance from the piping to enter the space. An example would be a bleed-pipe that may dump contents onto a drain that leads to a pipe connected to the confined space.

Under the definition there are two types of circumstances where piping or conduit in or near a confined space is not adjacent piping.

• A piping system that passes through the confined space: Such piping would not be considered to be adjacent piping if it is designed and maintained so there are no openings or other locations in the piping where leakage may occur, and work on or around the piping will not cause leakage. In such cases, measures must be adopted under section 9.4 (Control of hazards) to ensure worker safety when working in proximity to the piping. If any work in the space may result in leakage, then the piping must be treated as adjacent piping, in which case the control measures under section 9.18 apply. Leakage could occur for example, during a repair to a piping connection or replacement of a valve stem gland.



• Orifices between walls: In some configurations there are adjacent spaces with one or more orifices in a common wall between them. Section 9.18 is based on the use of control measures such as blanks, blinds, disconnects, and double block & bleed devices. A wall between two spaces is typically of a width and configuration that the use of such devices is not possible. As such, an orifice in a wall between a confined space and another space is not adjacent piping. Therefore, the blank, disconnect, double block and bleed, and blind requirements do not apply.
  
  However, the employer must ensure that workers are protected against any hazards associated with orifices under other provisions such as section 9.4 (Control of hazards). The application of section 9.4 means that the potential for fluid discharge into the confined space must be controlled so that the hazards to workers are eliminated or minimized.
  
  Examples of controls might include a gate over the orifice designed to prevent any leakage and secured in place so that it could not be dislodged from the closed position. For fluids that do not pose a vapour or gas hazard it may be appropriate to use a device to control fluid level in one of the spaces so that it does not rise to and flow through an orifice into the confined space where workers are present.

In the remainder of this guideline the isolation measures permitted under the various provisions of section 9.18 are discussed.

Application of section 9.18(1) - Basic isolation options
This provision specifies three basic options for isolating a confined space: disconnection, blanks, and blinds. It also permits the use of an engineered system that is equivalent to disconnecting, blanking, or blinding.

1. Disconnection: Means physically disconnecting adjacent piping from a confined space in a manner that prevents its contents from entering the space in the event of discharge. For example, if a pipe is disconnected, either a length of the pipe at least 10 times its diameter should be removed or the open ends of the disconnected pipe should be moved out of line so that leaks will not bypass the disconnection and continue into the confined space. In any disconnect procedure the requirements of the Regulation related to the protection of workers from contents of the piping must be complied with.



2. Blanking and blinding: Blanks and blinds are defined in section 9.1 of the Regulation as follows:
   
   

   "blank" means a solid plate installed through the cross-section of a pipe, usually at a flanged connection;
   
   "blind" means a solid plate installed at the end of a pipe which has at that point been physically disconnected from a piping system;

   
   

   In turn, "blanking or blinding" is defined as:

   ......the absolute closure of adjacent piping, by fastening across its bore a solid plate or cap that completely covers the bore and that is capable of withstanding the maximum pressure of the adjacent piping.

   
   

   The goal of a blank or blind is to eliminate any possibility of fluid entering a confined space. Since a conventional blank bisects flanges, if any fluid leakage were to occur it would discharge directly into the atmosphere. Fluid leakage cannot be allowed to pressurize an enclosed area, resulting in possible entry of leakage in the downstream portion of the pipe.

3. Equivalent engineered systems: For a device to be an "equivalent engineered system" to a blank, blind, or disconnect it must be engineered such that
   (a) any pipe contents leaking past the blocking device (such as a metal plate) is discharged directly to atmosphere
   (b) it is impossible for the pipe contents leaking past the blocking device to become pressurized in an area which will force the leaking contents to re-enter the pipe downstream of the blocking device
   (c) the system is designed on the assumption that seals leak
   
   Note: Some devices have been designed so they can be used either as a conventional valve, or as a line-blank. To be considered an engineered system equivalent to a blank, the openings to atmosphere around the means of blocking within these devices must be open to the atmosphere at all times, and the adjusting control for the devices must be locked out in the fully closed position when used as blanks. The style of device that requires the openings to atmosphere to be manually uncovered is not an equivalent engineered system.

Application of section 9.18(2) - Materials hazardous only because of pressure, temperature, or quantity
This provision applies to materials that are not toxic or corrosive, and are hazardous only because of pressure, temperature, or quantity. Typically this requirement applies to systems carrying water or steam. Three isolation options are outlined in the requirement

1. Controls meeting the requirements of section 9.18(1): This provision specifies the options of: disconnecting, blanking, blinding, equivalent engineered systems, and in certain cases a double block and bleed system. The restriction on the use of double block and bleed in section 9.18(1) is not considered to apply to water or steam.



2. De-energizing and locking out the pressure source: This control option applies to material inside adjacent piping when there is only one pressure source, typically either pressure due to pumps or the head pressure of fluids in lines. The latter is strictly the pressure in the pipe at the confined space location due to the force of gravity.
   
   For this provision to apply, the layout of the adjacent piping has to be such that if all of the valves are opened with pumps locked out, the fluid would not flow into the confined space. In such cases, then locking out the pumps and depressurizing the line provides sufficient control.



3. Other effective means: An example of a situation where other means would be considered effective is where in a waterworks system an engineered shutoff float in a chamber is used as a means to prevent water from rising to a height where it would be discharged via a pipe to a confined space. If the rate of flow could endanger workers if the float failed, a monitoring system and means of alerting workers would be needed to warn workers of any failure.

Application of section 9.18(4) - Prohibition on the use of valves
The use of one or more valves as a means of isolation is not permitted except in certain specified cases for substances that are hazardous only because of pressure, temperature, or quantity. If a substance is corrosive or toxic, the use of valves as a means of isolation is not permitted.

There are two circumstances where the use of valves is permitted as a means of isolation

• Where a double block and bleed system is permitted under section 9.18(2).
• Certain waterworks systems as permitted under section 9.18.1. (For more information, see OHS Guideline G9.18.1 Exemption on restriction of use of valves for isolation).

Application of section 9.18(5) - Gravity flow sewer systems
A p-trap may be used as a means of isolation if all the following conditions are met

1. The confined space is being isolated from a domestic sanitary or storm sewer.
2. The sewer system is gravity flow only at the point of isolation. (The p-trap option does not apply to locations in sewer systems that are pressurized by a pump.)
3. Work procedures are established that ensure that the integrity of the trap is assessed immediately upon entry.
4. The atmosphere is continuously monitored while workers are in the space and the atmosphere is shown to contain clean respirable air.

Examples of spaces where this provision could apply include any industrial or sewage system confined space facility that has a sink or other plumbed device that connects to a sewer system.

G9.18.1 Exemption to restriction on use of valves for isolation

Issued April 9, 2008

Regulatory excerpt
Section 9.18.1 (Exemption) of the OHS Regulation ("Regulation") states:

(1) In this section:

"public water supply system" includes valve and meter chambers and pressure reducing stations;

"dam water passageway" includes conduits, pipes, penstocks, power generating chambers, valves and related structures located within storage, diversion or other dams.

(2) Section 9.18(4) does not apply to water piping that is part of a public water supply system if the piping and associated equipment is designed, constructed, maintained and certified by a professional engineer to American Water Works Association standards.

(3) Section 9.18(4) does not apply to a dam water passageway if the structures of the passageway, including a gate valve or other flow control device, are certified by a professional engineer as being safe for workers to enter to perform the intended work.

Purpose of guideline
This guideline provides general information on the application of section 9.18.1, and specific information on each of the two types of exemptions: public water supply systems, and dam water passageways.

Application of section 9.18.1
This provision removes the restriction on the use of valving under section 9.18(4) in the following two circumstances:

• Public water supply systems that are designed, constructed, maintained, and certified by a professional engineer to American Water Works Association (AWWA) standards.



• Dam water passageways, as long as the structures of the passageways including valving and other flow control devices are certified by a professional engineer as being safe for entry.

Note that the examples of systems and passageways in the definitions in section 9.18.1 are not intended as comprehensive lists. For example, water mains and piping are not listed in the definition of public water supply systems, but are an integral part of them.

Certifications by engineers under section 9.18.1 will need to be available for review by a WorkSafeBC Prevention officer, where necessary to assess compliance with the requirements.

Information on each of the two types of circumstances in which the exemption applies is provided below.

Public water supply systems: The exemption applies to systems that provide water for domestic uses such as human consumption, food preparation, and cleaning purposes. It also applies to water distribution networks for fire suppression, which are typically an integral part of public water supply systems.

Note: In some cases, public water will be used downstream for industrial uses, for example in a process industry or a manufacturing facility. The exemption does not apply to such industrial systems. In these circumstances new hazards may be introduced, such as high pressures, temperature extremes, chemical additives, and the use of confined spaces that present hazards other than just water flow.

For a public water supply system to be covered by the exemption, the certification by an engineer is expected to address the design, construction, and maintenance of the system. It would typically be based in part on drawings, specifications, and records of installation and maintenance of components of the system. A significant element would be the assessment of current performance. The applicable information would be evaluated against AWWA standards. When issuing the certification, the professional engineer should specify the time period for which the certification would apply.

The AWWA maintains information on its standards at its web site, which can be accessed at http://www.awwa.org/Resources/Standards.cfm?ItemNumber=33777. The AWWA provides full print and CD-Rom sets of standards, as well as a selected set for small water systems. The AWWA has developed a substantial number of standards, only some of which would likely apply in specific situations. Many AWWA standards are also recognized by the American National Standards Institute (ANSI).

If a water supply system was constructed to a recognized standard other than AWWA (or ANSI where applicable), WorkSafeBC can consider accepting the alternate standard under the terms of section 4.4(2) of the Regulation. For a system installed before a recognized standard was in place, then an application can be made to WorkSafeBC for acceptability of the system under section 4.4(1).

Dam water passageways: The application of the exemption under section 9.18.1 is restricted to dam water passage ways. At a dam and associated hydroelectric station there may be a number of confined spaces, for example, fuel storage tanks, which are not part of the dam water flow system, and for which the exemption would not apply.

For confined spaces in which the exemption applies, engineering certifications specifically need to address the issue of worker safety. Such certifications are expected to be time limited, and the engineer will need to make the determination of applicable time period as part of the certification procedure.

G9.22-1 Alternate measures - Making submissions

Issued August 1, 1999; Editorial Revision October 2004; Editorial Revision February 7, 2006; Editorial Revision June 6, 2006; Editorial Revision June 22, 2007; Revised April 9, 2008

Regulatory excerpt
Section 9.22 (Alternate procedures) of the OHS Regulation ("Regulation") states:

(1) If isolation using the measures specified in section 9.18 is not practicable, the employer may implement alternate measures acceptable to the Board.

(2) All workers affected by measures implemented under subsection (1) must be informed of the measures taken and instructed in any applicable work procedures.

Purpose of guideline
This guideline outlines who an employer should contact at WorkSafeBC to determine if alternate measures under section 9.22 of the Regulation are acceptable, and the types of information to include in the submission. It also provides information on how WorkSafeBC will issue its decisions.

This guideline is the first in a series of guidelines on section 9.22. Additional guidelines outline frameworks for developing submissions on alternate measures in specific situations.

Contacting WorkSafeBC for acceptance of alternate measures
If an employer develops a set of alternate measures for a type of confined space covered by one of the framework guidelines in the G9.22 series, they should contact the Regional office of WorkSafeBC to determine acceptability. The applicant may be an employer who owns or operates the confined space, or may be a contractor doing work on or in it.

If an employer wants to implement alternate measures in circumstances that are not covered by one of the framework guidelines in the G9.22 series, the employer will need to contact the Regulatory Practices Department of the Worker and Employer Services Division of WorkSafeBC.

Note: In some cases a framework guideline may include a set of alternate measures considered to be acceptable in a specific situation. If an employer has workers who would be entering a confined space, or group of spaces, that would fall within the identified situation, and wishes to use the set of measures as an alternate means of isolation they may do so without the need to contact WorkSafeBC for an acceptance. Where such measures are included in a guideline they will be set off by a framed border.

What to include in the submission
A submission may cover a single confined space or a group of confined spaces that share similar characteristics. It should focus on the issues associated with isolation of the confined space, and cover the elements outlined below.

Main elements of the submission
The submission should address matters including

1. A brief description of the space, or the group of confined spaces with similar characteristics for which the submission is made
2. Why isolation using the measures specified in section 9.18 of the Regulation are not practicable
3. Contact information for the person who administers the confined space program, and for the qualified person who conducted the hazard assessment and prepared the alternate measures
4. A description of the hazards to be addressed by the alternate measures
5. The alternate measures that will be used to address the hazards, and how workers will receive protection from the hazards through use of the measures
6. How workers who are required to use the proposed measures will be informed of the measures taken and instructed in the applicable work procedures, as required by section 9.22(2)
7. How use of the alternate measures will be supervised
8. The time period for which the alternate measures will be needed

The submission should also include information from the joint OHS committee, or worker health and safety representative, as applicable, indicating their comments on the proposal, or other information that indicates the affected party has been consulted on the alternate measures. (Section 9.11(1)(b) of the Regulation requires consultation with these parties on confined space hazard assessment and written procedures.)

Information needed for Element #4 - hazards to be addressed
Hazards associated with the isolation of the confined space typically involve those arising from fluids such as liquids, gases, and vapours, and other materials such as slurries, dusts, and powders that could flow into the space. The submission should address matters such as the following, where applicable:

• Potential for material to flow into the space
• Characteristics of the material including pressure, temperature, quantity, toxicity, and corrosive properties
• Other hazards associated with the flow of material into the space, such as slips and falls, electric shock, reduced visibility, moving machinery, or equipment
• Review of historical air monitoring for site (if available and applicable)
• Any potential for work being done in the space to contribute to the likelihood of material flow into it

Information needed for Element #5 - alternate measures to be used
The measures chosen should be based on careful consideration of the hazards, and provide the most effective means of dealing with them. The submission should cover matters such as the following, where applicable:

• Engineered means of controlling flow, and related procedures
• Ventilation, where applicable, to ensure that hazardous gases, vapours, and other air contaminants from adjacent piping are kept below exposure limits, and no circumstances immediately dangerous to life and health, including oxygen deficiency, could occur
• Atmospheric testing, where applicable, if air contaminants could enter the space from adjacent piping while the space is occupied
• Monitoring of flow rates of materials and/or levels in the confined space
• The method of communication between a person or system for monitoring material flow and entry workers
• Emergency and rescue procedures in the event of any isolation system failure

Issuing a decision
Decision made by a WorkSafeBC Prevention officer: Where the circumstances of the confined space(s) for which the application is made are addressed by one of the framework guidelines in the G9.22 series, a Prevention officer responsible for the firm may make the decision on behalf of WorkSafeBC. As needed, the officer may contact Engineering or Regulatory Practices for advice. The officer will record their decision, including the terms of the decision and time period for which it is issued, in the text of an inspection report for the firm. The officer will provide a copy to the employer, who must post a copy at the worksite as required by the Regulation. Once the decision is made, the officer will forward the request and decision to Regulatory Practices.

Decision made by Regulatory Practices: Where an application for acceptance involves a situation not covered by a framework guideline in the G9.22 series, Regulatory Practices will issue the decision to the applicant using the standard format for Acceptance Request (AR) decisions. The applicant will post a copy of the decision and ensure copies are distributed to workplace parties, as required by the decision. Copies will be sent to the WorkSafeBC Regional Prevention manager and Prevention officer responsible for the firm, and to others who contributed information to the decision-making process.

Note: All decisions will focus on the issue of alternate measures for isolation of the confined space under section 9.22 of the Regulation. They will not, as a rule, address the issue of compliance with other provisions of the Regulation and must not be taken as an endorsement of the overall confined space program for the site.

G9.22-2 Alternate measures for confined spaces - Municipal sewage systems

Issued April 9, 2008

Regulatory excerpt
Section 9.22 (Alternate procedures) of the OHS Regulation ("Regulation") states:

(1) If isolation using the measures specified in section 9.18 is not practicable, the employer may implement alternate measures acceptable to the Board.

(2) All workers affected by measures implemented under subsection (1) must be informed of the measures taken and instructed in any applicable work procedures.

Purpose of guideline
This guideline outlines some issues to consider when developing alternate measures for municipal storm and sanitary sewage systems under section 9.22(1), where the isolation of adjacent piping under section 9.18 is not practicable.

Among other things, the guideline discusses

• How to make submissions on alternate measures to WorkSafeBC for circumstances covered by the guideline
• General hazard and control issues that can arise throughout sewage systems
• Information specific to three parts of sewage systems: piping, pumping stations and treatment plants

This guideline should be used in conjunction with OHS Guideline G9.22-1, which outlines elements that need to be addressed in any submissions to WorkSafeBC. Also, note that OHS Guideline G9.18, which provides interpretive information on terminology used with isolation procedures, may be of assistance.

NB. None of the information in this guideline is to be used as a substitute for the conduct of a site specific hazard assessment and development of associated safe procedures by a qualified person, as required under sections 9.9 - 9.11 of the Regulation.

Making a submission
A submission may cover a single confined space or a group of confined spaces that share similar characteristics. After developing proposed alternate measures for a space or spaces in a municipal sewage system, the employer will need to contact the local Regional office of WorkSafeBC to have the procedures reviewed by a WorkSafeBC Prevention officer for acceptability.

The focus of any submission on alternate measures should be on the fluids (including liquids, gases, and vapours), and other flowable materials that would be controlled by the isolation measures listed section 9.18.

For other land-based sewage systems, such as industrial systems which are not connected to municipal sewers, submissions should be made to the Regulatory Practices Department of the Worker and Employer Services Division of WorkSafeBC in Richmond. Note: the next guideline in this series (G9.22-3) discusses alternate measures for confined spaces on ships and other vessels that are undergoing repair or maintenance. Confined spaces on such vessels are likely to include on-board sewage systems.

General comments on hazards and alternate control measures in sewage systems
1. Hazards
For any sewage system, storm or sanitary, hazards that can be encountered include engulfment or immersion, exposure to toxic gases or vapours, oxygen deficiency, flammable atmospheres, slipping or tripping hazards, and electrical hazards where energized conductors or electrical equipment are exposed to damp conditions or liquid contact.

The potential for immersion will vary depending on factors including the frequency and volumes of discharges to the system, precipitation, and the relationship between the rate of possible fluid flow into the confined space to the dimensions of the space. For example, if the space is relatively small, and the diameter of inlet piping is substantial, there may be a relatively high potential for immersion. The contrary is the case where the floor area and volume of the space is large relative to possible fluid flows into it.

Water in sewage systems may be contaminated by materials such as oils from roadway runoff or industrial discharges, and in some cases materials such as ferrous chloride or other substances may be added for purposes of corrosion or odour control.

Air contaminants of concern in sewage systems include hydrogen sulfide, carbon monoxide, carbon dioxide, methane, ammonia, and organic vapours from oils or fuels that have entered the systems from roadway runoff. Decomposition gases such as hydrogen sulfide and methane can be a particular issue where sludge and other organic matter have been allowed to accumulate, and can be off gassed, particularly when the materials are disturbed. The term "sewer gas" is often used to refer to gases in sewage systems. It is an imprecise term, sometimes used in reference to hydrogen sulfide, but also to the complex mixture of gases that can be present.

In sanitary sewage systems, fluids may contain waterborne organisms that may cause disease (for example, hepatitis, giardiasis, and leptospirosis). Diseases affecting the gastrointestinal or respiratory systems have been reported among sewage workers.

Hazards from exposure to fluids and gases in piping may be complicated by other issues such as restricted visibility, limits to communication, and distance from exit points.

2. Alternate control measures
Various aspects of alternate control measures are discussed below, from fluid control to instruction and training.

• Fluid control: In some cases fluid flow can be controlled in sewage systems.
  Examples of fluid control techniques are
  
  • Inserting inflatable rubber bladders into pipes
  • Cutting into pipes to install removable sealing devices
  • Closing valves or gates
  • Installing mechanical blocking devices that consist of double seals designed so that the space between the seals may be monitored or pressurized to greater than the pressure of the hazardous fluid
  • Directing fluid flows through piping or channels adjacent to the space in question
  • Freezing of the pipe contents to form a plug in the pipe
  • Performing work when events such as tides ensure that the fluid level does not present a hazard

  The choice of method for fluid control will depend on what is feasible in the situation. In all cases the basic principle is that the most effective of the feasible methods should be chosen. Wherever manufactured devices are used, manufacturer's instructions and safe work practices must be followed. For example, the safe use of bladders will typically include measures such as cleaning the piping into which the bladder is placed, inflating the bladder only to permitted pressures, and securing the bladder so that it is not displaced in the pipe by a build up of pressure behind it.

  If devices that control the fluid flow are capable of being locked out then the requirements of Part 10 (De-energization and lockout) of the Regulation apply.

  The analysis of valves as a control measure should assume that all valves leak. However, there is no expectation that a properly installed and maintained valve will fail catastrophically if no work is being performed on it.

• Leakage of liquid and pumping: It is recognized that systems will often permit some leakage, and in that event, a means of pumping out the fluid may be necessary. A means of monitoring leakage coupled with procedures for evacuation in the event leakage rates or fluid levels exceed safety criteria is often a necessary feature of the safety system. Liquid level alarms or visual checks may be required to monitor liquid levels. It may be possible to set up a leakage check system from a central control location using camera monitors or other means.



• Air monitoring and ventilation: The historical record of atmospheric testing inside of the confined space needs to be considered along with the recent physical condition of the space. For instance, historical atmospheric testing during conditions of normal fluid flows may have not indicated atmospheric hazards. However, a space that has been left stagnant may have allowed material to decompose and create atmospheric hazards. The use of personal air monitors or other means of continuous monitoring will assist with worker safety where there is the potential for air contaminants to be present.
  
  Ventilation must be adequate, and be provided in conformity with the requirements in Part 9 (Confined spaces) of the Regulation.



• Communications: A means of communication with workers in the confined space will need to be provided and periodically verified as being effective.



• Personal protective equipment: Workers must be supplied with and use appropriate personal protective equipment as required by the Regulation to protect against hazards that cannot be eliminated.



• Slipping, tripping, and electrical hazards: Sewage systems are typically damp or wet environments, and appropriate measures must be taken regarding slipping, tripping, and electrical hazards. If fluid entering the confined space conceals trip and fall hazards such as floor holes or openings, these hazards need to be addressed, as well as any hazards involving the potential for liquid contact with energized conductors and equipment.



• Evacuation planning: Where there is a danger from the uncontrolled entry of liquid into the confined space, the time required to evacuate workers from the confined space needs to be shorter than the minimum possible time it would take fluid entering the confined space to create a condition that would impede exit from it. In general, the time is calculated using the maximum possible flow from the pipes that could be created by the failure of any single system element, and the relationship of that flow to the floor area of the space. The time required for evacuation should make allowance for possible problems during evacuation. The number, location, and types of exits are relevant in determining the evacuation time. Means of access and egress should be made as convenient as possible.
  
  It is recognized that in some cases catastrophic failure of the control system could lead to immediate danger to workers from fluid flow. For that reason isolation measures need to provide a high level of assurance that such circumstances will not occur. Evacuation measures need to be designed to minimize the time needed to exit, and rescue plans must be in place.
  
  Evacuation times in the event of development of harmful atmospheres may be more difficult to predict, and steps must be taken to ensure that personal protective equipment and rescue measures are up to the task. Depending on the potential exposure, workers in the confined space may be required to be permanently attached to a lifeline.



• Instruction and training: All workers affected by alternate measures must be informed of the measures taken and instructed in any applicable work procedures, including emergency measures. Workers also need to be informed of any residual hazards not fully controlled by other measures.
  
  Some considerations are provided in the remainder of this guideline for three typical parts of sewage systems: piping, pumping stations and sewage treatment plants.

Specific comments on piping, pumping stations, and treatment plants
1. Storm and sanitary sewage piping
When a worker enters a sewage pipe, the pipe itself is the confined space, not "adjacent piping" from which the space must be isolated as required by section 9.18. However, the feeder pipes that discharge into the pipe that is entered can be considered to be adjacent piping.

Often in such cases it may be impracticable to isolate the adjacent piping. In some cases partial or complete isolation may be possible with temporary dams, inflatable bladders, or other means such as rerouting of fluid flow.

However, in most cases alternate measures to ensure worker safety will involve a set of occupational hygiene and safety precautions other than or in addition to isolation.

When dealing with piping systems, there may be limits on the practicability of some standard occupational hygiene control measures. For example, ventilation as a means of assuring a safe atmosphere may not be practicable if the work must be done over a length of the piping system a substantial distance away from access points. However, wherever ventilation is feasible, it should be used, and it must always be provided where required by Regulation. If ventilation cannot assure a safe atmosphere, reliance may need to be placed on air monitoring and respiratory protection, including air supplied respirators where the circumstances warrant.

Hazards in piping will vary somewhat depending on whether the piping is a storm or sanitary sewer, or both. Often the piping will carry both storm and sanitary sewage in a combined system.

Sanitary sewers will have hazards associated with organic matter, including biological hazards, as well as air contaminants such as hydrogen sulfide or methane from the decomposition of organic matter. Such gases may be particularly an issue where sludge and other materials have been allowed to accumulate, and are subsequently disturbed. Where sewage flows at a rate of 2-3 feet per second (2-3 km/h) sedimentation and sludge build up is less likely. However, in such cases blockages can still occur where objects impede flow, or the diameter of the piping is an issue.

Flow volumes and rates will vary according to sewage discharge patterns in the catchment area and precipitation. Predicting patterns of flow will assist with worker safety.

Storm sewers will typically include hazards associated with water flows, which will vary with precipitation and drainage patterns in the area. Drainage from streets and parking areas is likely to be contaminated with oil and other hydrocarbon residues from vehicles. Also, where access locations to the sewers are in proximity to idling vehicles, for example at intersections and parking areas, there is the potential for exposure to exhaust gases including carbon monoxide.

Both sanitary and storm sewers may be contaminated with industrial or household chemicals, and with potentially harmful objects such as needles.

2. Sewage pumping stations
For pumping stations that are confined spaces the adjacent piping will typically be the sewer lines that feed into a reservoir or sump and the pipes used to discharge the sewage. There may also be drains that are arranged so that the contents of the drain could enter a sump and merge with the general sewage flow. Gases must be considered as well as liquids. Various means of controlling fluid flow may be possible. Given the proximity to a point of access, and the limited space involved, it should always be possible to provide effective ventilation into a pumping station.

The timing of events must also be considered in the hazard analysis. For instance the level and composition of off-gassing may depend on how long it has been since a channel or pipe has been emptied of residue. It may also be affected by the extent of liquid agitation and the surface area in contact with the atmosphere in partially filled pipes.

Knowledge of historical flow patterns and contamination problems could be of assistance in performing the required hazard analysis. Anticipated weather patterns may also affect the scheduling of the work inside of the confined space in order to minimize worker exposure to hazards of fluid flow.

3. Sewage treatment plants
Many of the hazards from fluid flow in sewage treatment plants are similar to those encountered elsewhere in sewage systems. Treatment plants offer certain advantages in terms of hazard control given that work activities occur at fixed sites and often above ground. The design of the system at the site may help ensure that the need for alternate measures is minimized.

Some of the hazard issues at the plants include chemicals used to treat sewage, potential for exposure to tidal water for facilities on the coast, and hazards arising from the treatment system. For example, the potential for hydrogen sulfide and methane to develop from the decomposition of organic material may be a particular issue in desludging operations in secondary sedimentation tanks, on the tops of sewage digesters, and in any tanker loading or unloading operations.

Sewage treatment plants may have channels that are connected by orifices or weirs. Such connections are not necessarily "adjacent piping." However, any hazards created by these adjacent channels need to be addressed. The hazards to workers from entry into channels will vary somewhat depending whether or not the channels are open or closed.

A means of fluid control that is possible in some circumstances is to channel fluid flow around the space in which worker entry is required. Alternate fluid control measures that can be used include sealing devices that are installed through holes drilled in the side of pipes and inflatable bladders. In such cases ensure that the manufacturer's instructions and other necessary safe procedures are followed.

Where discharge occurs into tidal water it may be possible to plan the timing of work so that ocean tides do not create a liquid hazard from the outlet side.

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