Justo Javier Clemente Hermoso
2. Tecnologías emergentes de sensorización y aplicaciones para la seguridad
A confined space is a hazard that wastewater workers encounter with great regularity.
Wastewater professionals are very familiar with confined spaces, such as manholes or storage tanks, but often overlook simple regular tasks in confined spaces, such as cleaning aerators in aeration basins, hosing down clarifiers, or even working in the subfloors of a building. A confined space is an accessible area with at least one of the following three conditions:
(1) Limited entrance and egress. There is typically one way in or out of the space.
(2) Unfavorable neutral ventilation (stale air). This is the most overlooked condi-tion for a confined space.
(3) A design that allows for limited occupancy. The design for the area is one that really is not made for continual occupancy.
TABLE5.2 A standard immunization program.
Infection Immunization
Hepatitis A Immunoglobulin treatment
Hepatitis B Three immunoglobulin vaccinations in a complete cycle
Influenza Annual flu vaccines
Measles Combined measles, mumps, and rubella (MMR) vaccines
Mumps MMR vaccines
Rubella MMR vaccines
Tetanus and diptheria TD vaccine
Pnuemoccal disease Pnuemococcal polysaccharide disease
Many deaths, injuries, and job-related illnesses in the wastewater treatment indus-try result from occupancy in confined spaces or from hazards found in these spaces, such as toxic gases, oxygen deficiency, or engulfment. The following sections discuss some of the characteristics of confined spaces and the necessary precautions in more detail.
LIMITED ENTRY AND EGRESS. Confined spaces are limited by the entry and exit, by either size or location. Openings are typically small. Some openings are smaller than the standard 610-mm (24-in.) manhole openings. They are difficult to move through and pose a particular hazard if there is the need for an emergency retrieval. If a person must contort the body to get into the opening, getting an unmoving and un-cooperative body out is even more difficult. It would not be unusual to have PPE, such as a respirator, hard hat, face shields, or SCBA, dislodged by the small opening. Keep in mind, not all confined spaces are defined by small openings, but could be aeration basins, digesters, or clarifiers that are difficult to enter or exit. Open top spaces could be excavations or the previously mentioned ones and would require a ladder or hoists to enter or exit. Being rescued from areas like this may be easier than from small open-ings, but require specialized equipment and at least one spotter or helper.
VENTILATION HAZARDS. A ventilation hazard may as simple as stale air or oxygen deficiency but can also be dangerously high levels of gases, such as hydro-gen sulfide, carbon monoxide, or even carbon dioxide. There also can be explosive gases in the confined space. These can be particularly dangerous in areas such as manholes or lift stations, when a worker has no control or advance notice of the problem. The atmosphere may be so oxygen-rich that it also becomes a hazard. Later in this section, some of the more common gases will be defined and their hazards will be listed.
LIMITED OCCUPANCY. Most confined spaces not only have limited access, but are not designed to have continuous occupancy. They are designed, at best, to have short-term occupancy for maintenance or repair, cleanup, or similar tasks. These tasks are often dangerous because of the chemical or physical hazards they can pose, often in a limited-visibility situation.
Hazards. The following are hazards that may be found in a confined space:
• Oxygen-deficient atmosphere. If the oxygen content is or drops below 19.5%, a worker should avoid entering a confined space or should leave that space
immediately. Use of an oxygen sensor is necessary when entering a confined space and should be worn while in that space. Entry to an oxygen-deficient at-mosphere should not be attempted without SCBA.
• Flammable atmosphere. There may be methane present from the decomposition of organic materials, or someone may pour flammables, such as gasoline, down the sewer. Any ignition source could cause an explosion or start a fire in such an atmosphere. There may be times when the upper explosive limit (UEL) of a flammable gas is exceeded before ventilation is applied. This means that the gas will not combust. When ventilation is applied, it could then be explosive. Moni-toring while in the combined space by a gas monitor is a good practice for these reasons.
• Toxic atmosphere. Some gases and vapors, if present in a confined space, may be toxic, even if not flammable. The atmosphere inside a confined space may change while a person is working in it. There have been times when the atmos-phere inside a confined space was above the UEL and the space was ventilated, which, in actuality, brought the working conditions in the space to a greater hazard limit as the concentration of the gas decreased to below the UEL. Fumes from equipment that is used may accumulate in the space (i.e., carbon monoxide from a combustion engine on a pump), or cleaning chemicals being used may give off vapors.
• Temperature extremes. Extremely hot or cold temperatures in a confined space can affect or injure workers. Again, temperatures may rise or fall while working in a confined because of equipment being used. Because of the chance of smaller air exchange through smaller entrances, temperatures can stay warmer or colder for long periods of time.
• Engulfment hazards. Materials stored in a bin or hopper can engulf or suffocate a worker. Chemicals, grain, and sand are typically stored in hoppers. If a worker is in an area such as the bottom of a clarifier or digester or pumping station, he or she should be sure that some sort of lockout/tagout (discussed later in this chapter) is used to ensure that fluid cannot engulf him or her.
• Noise. A confined space is a great echo chamber. When a person is in a confined space and the sound can do nothing other than assault a person’s hearing, dam-age could occur. The sound can come from either inside or outside of the cham-ber and impair speech or drown out shouting.
• Slick or wet surface. Confined spaces often have a wet surface, which can be slippery and dangerous for maneuvering within it.
• Falling objects. It is important to be aware of the possibility of objects entering a confined space and falling on someone. This could be as simple as a person
walking by and unknowingly kicking a rock into the hole or unsafely throwing tools into and out of the hole. Use common sense and a rope and a bucket for such operations.
Precautions. The following are safe work practices that are recommended before entering a confined space:
• Air monitoring. More precisely, this should be called atmosphere monitoring.
First, the air is sampled with an oxygen sensor. There must be a minimum of 19.5% oxygen present before a person can go into the space. The worker should be sure the oxygen is measured at the levels he or she must pass through and the level where he or she will be working. There can be a stratification of gases caused by poor ventilation that could be oxygen-deficient. A gas monitor should always be used to check for the presence of explosive or deadly gases.
Most four-gas detectors monitor for oxygen, combustibles, carbon monoxide, and hydrogen sulfide; however, with plug-in modules now available, some of these can be reconfigured to sample other gases. Air monitors must routinely be cali-brated and tested with “bump gas” per manufacturer specifications. When work-ing within a confined space, a worker should wear a portable detector to mon-itor atmospheric conditions and possible deadly changes. The oxygen sensor/
broad-range sensor is best-suited for initial use in situations where the actual or potential contaminants have not been identified because broad-range sensors, unlike substance-specific sensors, enable employers to obtain an overall read-ing of the hydrocarbons (flammables) present in the space. However, such sen-sors only indicate that a hazardous threshold of a class of chemicals has been exceeded. They do not measure the levels of contamination of specific sub-stances. Therefore, substance-specific devices, which measure the actual levels of specific substances, are best-suited for use where actual and potential conta-minants have been identified.
• Ventilation. The confined space should have general ventilation or localized exhaust ventilation in place before entry and during occupancy. It is important to be sure that the air being used to ventilate the space is not pulling in toxic fumes from the outside (diesel fuel, gasoline vapors, etc.).
• Personal protective equipment. Respiratory equipment is essential for safe con-fined space entry. If a worker can be sure that the atmosphere is safe and that there is little chance it will change, PPE may not be necessary. If an oxygen-deficient atmosphere exists, workers will need to wear a SCBA. If the space cannot be entered while the worker is wearing the SCBA, equipment supplying forced
outside air or escape respirators may be used (such as a self-rescuer for mining).
Workers need to be fit-tested for a respirator or an SCBA before using one, and workers with beards cannot wear one. It is important to remember that air-puri-fying respirators may only filter out or neutralize certain contaminants at specific concentrations. Atmospheres with oxygen concentrations that are either too high or too low cannot be made safe by using air-purifying respirators. Workers’
questions should be directed to their supervisor or industrial hygienist.
• Labeling and posting. In a work environment, all confined-space entrances should be posted. The labels should clearly be marked so that all employees can understand them.
• Training. As with chemical hazards, all workers who must work around con-fined spaces need routine training, including knowing how to identify concon-fined spaces, use air analyzers, and define permit-required spaces. They should be fa-miliar with rescue procedures and communication in confined work spaces and complete lockout/tagout training and attendant training. Periodic follow-up training is recommended to reinforce safe work practices. This training should be evaluated to make sure that it is effective and current (a video that has been shown to workers multiple times will lose its effectiveness).
• Medical surveillance. Employees who must use a SCBA respirator to work in a confined space to perform their duties need to have their lung capacities checked annually and obtain medical clearances in addition to completing annual fitness tests.
• Isolation. The supervisor for any confined-space entry must be aware of any hazards that may exist. It is the supervisor’s responsibility to lock up any lines and valves that may cause engulfment hazards. Also, electrical lockout/tagout procedures need to be followed. If an entrant notices any possible hazards that were not covered, he or she should communicate them to the supervisor.
• Attendant. Any time there is a confined-space entry, there should be an atten-dant whose sole duty is to communicate with entrants and make sure that they are not in danger. This may mean using a common sign language or radios (if the entrant gets out of the line of sight). It is also the attendant’s responsibility to bring the entrant out using a harness and tripod if there are problems. This means the attendant cannot be performing traffic control, wandering off, or talking on the cell phone. The person below trusts the attendant with his or her life. No one should ever follow a collapsed fellow worker into a confined space.
Often, there has been a rapid change of atmosphere that has caused the worker to collapse; when another worker enters the same atmosphere, he or she has just removed the victim’s chance of rescue.
• Tripod and harness. The person entering a confined space should wear a har-ness. There are too many variations of harnesses to list; the best source for view-ing them would be safety catalogs. An effective harness should allow the person being removed to be lifted straight up out of the confined space without forcing their head and neck to awkward angles. Harnesses should be comfortable to work in. One size does not fit all. Often, safety supply companies will allow cus-tomers to try on their stock before purchase to see if it works for the individuals.
Tripods or lifting cranes are again varied and depend on the application. The tri-pod that fits over a manhole will not work to pull someone safely out of a deep clarifier or digester. There are even lifts designed to fit into mounts on bumpers of wastewater service vehicles for sewer lines. Maintenance of equipment and practice are essential to getting someone out of a dangerous situation safely.
• Procedures. There should be written procedures (typically in the form of a checklist) to be completed before entry to a confined space. When these proce-dures are followed and completed, the chances of injury decrease. A sample checklist will follow in this chapter. These procedures must be practiced. A life-or-death situation is no time to find out that something is not understood or that some procedures have been bypassed.
PERMIT-REQUIRED VERSUS NON-PERMIT-REQUIRED CONFINED SPACES. There is a distinct difference between these types of confined spaces. A per-mit-required confined space is one that meets the definition of a confined space and has one or more of the following characteristics:
• Contains or has the potential to contain a hazardous atmosphere,
• Contains a material that has the potential for engulfing an entrant,
• Has an internal configuration that might cause an entrant to be trapped or as-phyxiated by inwardly converging walls or by a floor that slopes downward and tapers to a smaller cross section, and/or
• Contains any other recognized serious safety or health hazards.
It is the on-site supervisor’s responsibility to determine whether the space is a permit-required confined space. To comply with OSHA Title 29 CFR Part 1910.146 (Permit Required Confined Spaces, 2005) (the rules that govern confined spaces), entry to a per-mit-required confined space requires that certain actions be performed by the employer:
• Follow the general requirements of paragraph (c) of the standard;
• Have a permit-required confined-pace program that complies with paragraph (d) of the standard;
• Follow the permit system requirements of paragraph (e) of the standard;
• Complete the entry permit as required in paragraph (f);
• Comply with employee training requirements of paragraph (g);
• Ensure that authorized entrants, attendants, and entry supervisors know their responsibilities as required in paragraphs (h), (i), and (j);
• Provide for rescue and emergency services as stated in paragraph (k); and
• Ensure that employees are allowed participation in these processes as required in paragraph (l) of the standard.
In general, employers must evaluate the workplace to determine if spaces are permit-required confined spaces (see Figure 5.5). If there are permit-permit-required confined spaces in the workplace, the employer must inform exposed employees of the existence, loca-tion, and danger posed by the spaces. This can be accomplished by posting danger signs or by another equally effective means. If employees are not to enter and work in permit-required confined spaces, employers must take effective measures to prevent their employees from entering them. If employees are expected to enter these spaces, employers must comply with all requirements of the OSHA standard.
Requirements of a Written Program. If the employer allows employee entry to a permit-required confined space, a written program must be developed and imple-mented. Among other things, the OSHA standard requires the employer’s program to do the following:
• Identify and evaluate permit space hazards before allowing employee entry.
• Test conditions in the permit space before entry operations and monitor the space during entry.
• Perform, in the following sequence, appropriate testing for atmospheric haz-ards: oxygen, combustible gases or vapors, and toxic gases or vapors.
• Implement necessary measures to prevent unauthorized entry.
• Establish and implement the means, procedures, and practices (such as specify-ing acceptable entry conditions, isolatspecify-ing the permit space, providspecify-ing barriers, verifying acceptable entry conditions, purging, making inert flushing, or venti-lating the permit space) to eliminate or control hazards necessary for safe permit-space entry operations.
• Identify employee job duties.
• Provide, maintain, and require the use of PPE and any other equipment neces-sary for safe entry (e.g., testing monitoring, ventilation, communications, light-ing equipment, barriers, shields, and ladders).
Permit – Required Confined Space Decision Flow Chart
*Spaces may have to be evacuated and reevaluated if hazards arise during entry.
Does the workplace contain PRCS as defined by 1910.146(b)? Consult other applicable OSHA standards.
Inform employees as required by 1910.146(c)(2).
Will permit space be entered.
Prevent employee entry as required by 1910.146(c)(3).
Do task from outside of space.
Will contractors enter?
Task will be done by contractors’ employees. Inform contractor as required by 1910.146(c)(8)(i), (ii) and (iii). Contractor obtains information required by 1910.146(c)(i), (ii) and (iii) from host.
Both contractors and host employees will enter the space.
Coordinate entry operations as required by 1910.146(c)(8)(iv) and (d)(11). Prevent unauthorized entry.
Will host employees enter to perform entry tasks?
Prevent unauthorized entry.
Does space have known or potential hazards?
Can the hazards be eliminated?
Not a PRCS. 1910.146 does not apply. Consult other OSHA Standards.
Employer may choose to reclassify space to non-permit using 1910.146(c)(7).
Can the space be maintained in a condition safe to enter
by continuous forced air ventilation only? Space may be entered under 1910.146(c)(5).
Prepare for entry via permit procedures.
Verify acceptable entry conditions (Test results recorded, space isolated if needed, rescuers/means to summon available, entrants properly equipped, etc.)
Permit not valid until conditions meet permit specifications.
Permit issued by authorizing signature. Acceptable entry conditions maintained throughout entry.
Entry tasks completed. Permit returned and canceled.
Audit permit program and permit based on evaluation of entry by entrants, attendants, testers and preparers, etc.
Emergency exists (prohibited condition). Entrants evacuated, entry is aborted. (Call rescuers if needed). Permit is void. Reevaluate program to correct/prevent prohibited condition. Occurrence of emergency (usually) is proof of deficient program. No re-entry until program (and permit) is amended. (May require new program).
FIGURE5.5 Permit-required confined space (PRCS) decision flowchart (http://www .cehs.siu.edu/occupational/confined_space/flowchart.htm; accessed March 2006).
• Ensure that at least one attendant is stationed outside the permit space for the duration of entry operations.
• Coordinate entry operations when employees of more than one employer are to be working in the permit space.
• Implement appropriate procedures for summoning rescue and emergency services.
• Establish, in writing, and implement a system for the preparation, issuance, use, and cancellation of entry permits.
• Review established entry operations and annually revise the permit space entry program.
• When an attendant is required to monitor multiple spaces, implement the pro-cedures to be followed during an emergency in one or more of the permit spaces being monitored.
If hazardous conditions are detected during entry, employees must immediately leave the space, and the employer must evaluate the space to determine the cause of the haz-ardous conditions.
When entry to permit spaces is prohibited, the employer must take effective
When entry to permit spaces is prohibited, the employer must take effective