Confined Spaces FAQs

Under the requirements at 1910.146(c)(1) and (2), the employer must evaluate the workplace to determine if any spaces are permit-required confined spaces. And, "If the workplace contains permit spaces, the employer shall inform exposed employees, by posting danger confined spaces signs or by any other equally effective means, of the existence and location of and the danger posed by the permit spaces. Note: A confined spaces sign reading ‘DANGER - PERMIT-REQUIRED CONFINED SPACE, DO NOT ENTER' or using other similar language would satisfy the requirement for a sign." OSHA does not require employers to document the evaluations.

OSHA's permit-required confined spaces standard defines "confined space" and "permit-required confined space (permit space)" at 1910.146(b). OSHA defines a confined space as meeting the following criteria:

1. Is large enough for an employee to bodily enter and work;
2. Has limited or restricted means of entry and exit; and
3. Is not designed for continuous occupancy.

If you determine that a space does meet the definition of "confined space," then you need to further evaluate the space to determine whether it meets the definition of "permit-required confined space." A permit-required confined space is a confined space that has one or more of the following characteristics:

1. Contains or has a potential to contain a hazardous atmosphere; or
2. Contains a material that has the potential for engulfing an entrant; or
3. Has an internal configuration that could trap or asphyxiate an entrant by inwardly converging walls or a floor which slopes downward and tapers to a small cross section; or
4. Contains any other recognized serious safety or health hazard.

OSHA only requires this initial evaluation. There is no requirement for the employer to reevaluate the workplace for spaces that may be permit spaces. However, any space that you have previously identified as a non-permit confined space does need to be reevaluated under 1910.146(c)(6): if "there are changes in the use or configuration of a non-permit confined space that might increase the hazards to entrants, the employer shall reevaluate that space and, if necessary, reclassify it as a permit-required confined space." Again, OSHA does not require employers to document the evaluations.

At 1910.146(c)(3), the standard states: “If the employer decides that its employees will not enter permit spaces, the employer shall take effective measures to prevent its employees from entering the permit spaces and shall comply with paragraphs (c)(1), (c)(2), (c)(6), and (c)(8) of this section.”

These are the requirements to: identify permit spaces in the workplace, inform workers about the spaces, reevaluate non-permit confined spaces when there are changes in their use or configuration, and cooperate with contractors who will enter the permit spaces.

A good practice is to somehow bar or lock the potential entry portals when employees will not enter a permit space.

An OSHA letter of interpretation dated Sept. 21, 2006, addresses the requirements to inform employees about the dangers by posting signs or using equally effective means. The following is from the Sept. 21, 2006, letter:

Employers who are providing sufficient training to protect their employees effectively need not post dangers signs at permit-spaces. Regardless of whether signs are used, the standard requires that the employer inform employees exposed to the hazards posed by permit spaces of the existence, location, and danger of those spaces. In enforcing §1910.146(c)(2), OSHA will check to ensure that methods other than warning signs are truly effective in imparting the required information to employees. General training in the permit-required confined space standard, for example, cannot be expected to adequately inform employees of the location of permit spaces in the workplace. The standard places the burdens of identifying the spaces and of controlling the resultant hazards on the employer not on the employees. However, OSHA does not require the posting of any permit space whose only means of access necessitates the use of tools or keys, provided that the employees (if any) who are expected to gain entry into these spaces are trained. Further, paragraph (c)(3) requires employers to take effective measures to prevent their employees from entering permit spaces. It appears in your case that employees will enter some permit spaces but will be prohibited from entering others. Whatever measures you take, employees should be clear on which specific permit spaces they are not allowed to enter.

OSHA defines a confined space as meeting all of the following criteria:

1. Is large enough for an employee to bodily enter and work; and
2. Has limited or restricted means of entry and exit; and
3. Is not designed for continuous occupancy.

If the entrants may freely step into and out of the space without having to step over a raised threshold or stoop under the door opening, and if equipment in the space or the travelling distance to the exit could not interfere with the entrants ability to escape in an emergency, then there would be no limited means of entry or exit. If this is the case, then the space does not meet the definition of "confined space."

OSHA's compliance directive, CPL 2.100 - Application of the Permit-Required Confined Spaces (PRCS) Standards, includes the following guidance in Section (b) of Appendix E:

1. Under what circumstances will stairs or ladders constitute a limited or restricted means of egress under the standard?
   "Ladders, and temporary, movable, spiral, or articulated stairs will usually be considered a limited or restricted means of egress. Fixed industrial stairs that meet OSHA standards will be considered a limited or restricted means of egress when the conditions or physical characteristics of the space, in light of the hazards present in it, would interfere with the entrant's ability to exit or be rescued in a hazardous situation.
2. Does the fact that a space has a door mean that the space does not have limited or restricted means of entry or exit and, therefore, is not a ‘confined space'?
   A space has limited or restricted means of entry or exit if an entrant's ability to escape in an emergency would be hindered. The dimensions of a door and its location are factors in determining whether an entrant can easily escape; however, the presence of a door does not in and of itself mean that the space is not a confined space. For example, a space such as a bag house or crawl space that has a door leading into it, but also has pipes, conduits, ducts, or equipment or materials that an employee would be required to crawl over or under or squeeze around in order to escape, has limited or restricted means of exit. A piece of equipment with an access door, such as a conveyor feed, a drying oven, or a paint spray enclosure, will also be considered to have restricted means of entry or exit if an employee has to crawl to gain access to his or her intended work location. Similarly, an access door or portal which is too small to allow an employee to walk upright and unimpeded through it will be considered to restrict an employee's ability to escape.
3. Can the distance an employee must travel in a space such as a tunnel, to reach a point of safety be a determinant for classifying a space as a confined space?
   Yes. The determination would most likely be a function of the time of travel to the point of safety.

If the space does not meet the definition of "confined space," no entry permit is required. The employer must address whatever hazards are present by complying with other applicable standards and the general duty clause. (Under Section 5(a)(1) of the OSH Act of 1970, the employer has a responsibility to provide "a place of employment which is free from recognized hazards that are causing or are likely to cause death or serious physical harm to his employees." OSHA can issue General Duty Clause citations in hazardous situations where there is no applicable OSHA standard.

A space may be large enough inside for an employee to enter and work, but the portal to the space may be very small. A confined space (and a permit-required confined space) must have an entry port that is large enough to allow full-body entry. If the entrance is too small for a worker to completely enter, or if the space itself is too small for a worker to completely enter, then OSHA's standard does not apply. OSHA does not specify any minimum size for an opening to be considered large enough for an employee to bodily enter.

Non-Mandatory Appendix F of the permit-required confined spaces standard discusses rescue team or rescue service evaluation criteria. In part B. 10. 3. of the section on peformance evaluation, it mentions rescue restrictions related to portal size. It states:

(3)Portal size.
(a) Restricted -- A portal of 24 inches or less in the least dimension. Portals of this size are too small to allow a rescuer to simply enter the space while using SCBA. The portal size is also too small to allow normal spinal immobilization of an injured employee.
(b) Unrestricted -- A portal of greater than 24 inches in the least dimension. These portals allow relatively free movement into and out of the permit space.

Section III of the preamble to the final rule as published in the Jan. 14, 1993, Federal Register states the following about small spaces:

... While OSHA is concerned that spaces that are too small for complete bodily entry may pose hazards for employees, the Agency did not intend to cover such spaces under the permit space standard. ... Since an employee cannot totally enter such spaces, he or she should not have difficulty withdrawing from the space. In order for a space to be considered a permit-required confined space, it must first be a confined space. A space that cannot be entered is not confined; therefore, it does not pose hazards related to the difficulty of exiting the space.
OSHA realizes that an employee may still be injured or killed as a result of some atmospheric hazard within such an enclosed area; however, this standard is not intended to address all locations that pose atmospheric hazards. ...

OSHA's permit-required confined spaces standard defines "entry" at 1910.146(b): "Entry means the action by which a person passes through an opening into a permit-required confined space. Entry includes ensuing work activities in that space and is considered to have occurred as soon as any part of the entrant's body breaks the plane of an opening into the space."

Two scenarios to consider are reaching in through a portal that is large enough to bodily enter and reaching into a small portal that opens into a permit space (a small portal in addition to the main entry hatch).

An OSHA letter of interpretation dated Oct. 18, 1995, includes the following:

When any part of the body of an entrant breaks the plane of the opening of a PRCS large enough to allow full entry, entry is considered to have occurred and a permit is required, regardless of whether there is an intent to fully enter the space. If a part of the body were placed in an opening through which the worker could not pass into the permit-required confined space, no PRCS entry will have occurred. However, if entry by only part of the body does not expose the entrant to the possibility of injury or illness, then the violation may be considered a ‘de minimis' violation. (A de minimis violation is one in which a standard is violated, but the violation has no direct or immediate relationship to employee safety or health. These violations are documented but no citations are issued.)
Examples of situations where entry by only part of the body into a PRCS would not expose an entrant to the possibility of injury or illness are as follows:
1. An entrant reaches through the opening of a horizontal PRCS, which is so classified only because it contains exposed live electrical parts ten feet from the opening.
2. An entrant put his head through the opening of an overhead PRCS, which is so classified only because it contains unguarded rotating parts ten feet from the opening.
Examples of situations where entry by only part of the body into a PRCS can expose an entrant to the possibility of injury or illness are as follows:
1. An entrant can possibly suffer a burn while reaching into a PRCS, which is so classified because it contains a thermal hazard.
2. An entrant can possibly fall into a below grade PRCS while standing on a vertical ladder in the opening of the space, which is so classified because it contains an oxygen deficient atmosphere.
3. An entrant can possibly become unconscious as result of his head accidentally entering a PRCS while they are reaching into a PRCS, which is so classified because it contains an oxygen-deficient atmosphere. ...
It should be noted that an employer is obligated to take appropriate steps to protect employees reaching into a space which is not a PRCS, if such an action exposes an employee to an injury or illness.

Employees involved with permit space entry procedures need training to meet the requirements outlined at 1910.146(g). Paragraph (g)(2) sets out the conditions under which training is to be provided:

Training shall be provided to each affected employee:
(i) Before the employee is first assigned duties under this section;
(ii) Before there is a change in assigned duties;
(iii) Whenever there is a change in permit space operations that presents a hazard about which an employee has not previously been trained;
(iv) Whenever the employer has reason to believe either that there are deviations from the permit space entry procedures required by paragraph (d)(3) of this section or that there are inadequacies in the employee's knowledge or use of these procedures.

The duties of authorized entrants are outlined at 1910.146(h), the duties of attendants are at 1910.146(i), and the duties of entry supervisors are at 1910.146(j). If your employees are also designated to provide rescue and emergency services, those employees must meet the requirements at 1910.146(k)(2).

The standard does not include a requirement for annual or other regularly-scheduled training in addition to the above.

Employers are required to review the permit program annually (see 1910.146(d)(14)), and there is a requirement that employee rescue service personnel must make practice rescues at least once every 12 months (see 1910.146(k)(2)(iv)).

OSHA discusses refresher training in the preamble to the permit-required confined spaces final rule (published in the January 14, 1993 Federal Register). The following excerpt is from the preamble's Section III:

OSHA acknowledges the need for refresher training. Paragraphs (g)(2)(ii), (g)(2)(iii), and (g)(2)(iv) require 'refresher' or 'follow-up' training whenever there is a demonstrated need for it. Changes in assigned permit space program duties or exposure to hazards for which an employee has not been trained are obvious indications of a need for additional or refresher training. Similarly, any deficiency noted in an employee's work performance that is related to the safety and health of entrants would probably be a strong indication of the need for training for that employee. If training proves to be insufficient to improve the employee's performance (eliminate the unsafe acts), the employer then might consider other means of action, such as clarification of the procedures involved or disciplinary action. However, OSHA believes that training is normally the primary corrective action to be taken. Other evidence of the need for additional training may be brought out in the review of permit space program under paragraphs (d)(13) and (d)(14) of the final rule.
Certainly, incidents during entry operations that employees were nearly injured are evidence of a possible need for additional training. The Agency believes that paragraph (g)(2) of the final rule will ensure that employers provide ongoing training to their employees and evaluate their permit space programs to confirm that employees have the understanding, knowledge, and skills needed for safe permit space entry operations.

Yes, the entry supervisor may also be the attendant or the authorized entrant. Employees must be trained on all of the duties they are to perform.

A note to the standard's definition of "entry supervisor" at 1910.146(b) states: "Note: An entry supervisor also may serve as an attendant or as an authorized entrant, as long as that person is trained and equipped as required by this section for each role he or she fills. Also, the duties of entry supervisor may be passed from one individual to another during the course of an entry operation."

Under 1910.146(c)(7), a permit space may be reclassified as a non-permit confined space if the space poses no actual or potential atmospheric hazards and if all hazards within the space are eliminated without entry into the space. If you reclassify the space as non-permit according to the criteria in 1910.146(c)(7), you are exempted from the requirements in 1910.146 (d) through (k).

That reclassification would remain in effect as long as the hazards remain eliminated. It would allow employers to have employees enter the space without implementing a permit space program.

The elimination of the hazards can be accomplished by emptying the space of materials that pose an engulfment hazard and applying lockout/tagout to meet 1910.147. However, other provisions must be in place if a leak in a pipe opening in the space could lead to a hazardous atmosphere.

The following excerpt from an OSHA letter of interpretation dated Nov. 15, 1993, discusses reclassification as it relates to the potential for atmospheric hazards to develop:

We agree that through the application of 1910.147, the hazards of stored energy and moving machinery would be eliminated. We do not agree that lockout-tagout would eliminate the natural gas hazard. Hazard elimination in that case would require one of the techniques (blanking, blinding, misaligning or removing sections of lines or pipe, and double block and bleed system) referenced in the definition of isolation' (see paragraph (b) of 1910.146).
Item 2 indicates that a cool down time is allotted so that the latent heat of the oven does not create a heat exposure hazard. We concur with the cool down practice to eliminate this heat stress potential. However, we suggest the actual job safety practice indicate a maximum oven temperature allowable or other measurable parameter (period of time) allotted before entry.

You may want to review the following definitions at 1910.146(b):

"Double block and bleed" means the closure of a line, duct, or pipe by closing and locking or tagging two in-line valves and by opening and locking or tagging a drain or vent valve in the line between the two closed valves.
"Isolation" means the process by which a permit space is removed from service and completely protected against the release of energy and material into the space by such means as: blanking or blinding; misaligning or removing sections of lines, pipes, or ducts; a double block and bleed system; lockout or tagout of all sources of energy; or blocking or disconnecting all mechanical linkages.
"Line breaking" means the intentional opening of a pipe, line, or duct that is or has been carrying flammable, corrosive, or toxic material, an inert gas, or any fluid at a volume, pressure, or temperature capable of causing injury.

The alternate entry procedures at 1910.146(c)(5) can be used when the only hazard in a permit-required confined space is an atmospheric hazard that can be controlled through continuous forced air ventilation. If the entry operation is done using the alternate entry procedures, the employer does not need to meet 1910.146(d) through (f) and (h) through (k).

The following is from Appendix E of OSHA's compliance directive, CPL 02-00-100, Application of the Permit-Required Confined Spaces (PRCS) Standards, 29 CFR 1910.146:

6. How will an employer determine a ‘safe for entry' level for contaminants under the provisions of paragraph (c)(5)?
OSHA is willing to accept as the minimal ‘safe for entry' level, that which is 50% of the flammable or toxic substance that would constitute a hazardous atmosphere. The two examples footnoted on page 4488 of the preamble to the final rule are:
(1) The LFL for methane is a concentration of 5 percent by volume. Ten percent of this value is 0.5 percent, a concentration which would be considered hazardous by definition. Under the guideline the measured concentration of methane cannot exceed 0.25 percent after ventilation in order for the procedures specified in paragraph (c)(5)(ii) of the final rule to be acceptable.
(2) The 8-hour time weighted average PEL for chlorine, under Table Z-1, is 1.0 parts per million. This concentration of chlorine would be considered hazardous by the definition of "hazardous atmosphere". Under the guideline, the measured concentration of chlorine cannot exceed 0.5 parts per million after ventilation in order for the procedures specified in paragraph (c)(5)(ii) of the final rule to be acceptable.

The January 1993 preamble to the final rule mentions this 50 percent safety factor and includes the following in Section III-Summary and Explanation of the Standard:

Additionally, the work to be performed within the space must not introduce any hazards - work with hazardous quantities of flammable or toxic substances and hot work are not permitted. This type of work would introduce hazards beyond those accounted for by the determination that the permit space can be maintained safe for entry. Paragraph (c)(5)(i)(B) indicates clearly that an employer who relies on continuous forced air ventilation to maintain spaces safe for entry must be able to establish that other measures are not needed to protect entrants.

Under 1910.146(d)(5), employers must evaluate the conditions of the permit space, and "when testing for atmospheric hazards, test first for oxygen, then for combustible gases and vapors, and then for toxic gases and vapors." It remains up to the employer to implement testing that effectively evaluates the hazards in any permit space entry operation.

OSHA's discussion of atmospheric testing in Section III of the preamble to the final rule published January 14, 1993, includes the following:

The type of testing that needs to be performed is dependent on the hazards that are present within the space. For permit spaces posing atmospheric hazards, atmospheric testing would be necessary. For other hazards, different tests will be necessary. For example, if the permit space poses thermal hazards, the temperature within the space would need to be tested. Paragraph (d)(5)(i) requires the employer to conduct whatever tests are necessary to ensure that acceptable entry conditions are present. [bold emphasis added.]

OSHA discusses the hazards of permit spaces in Section II of the preamble:

OSHA presents the following examples regarding atmospheric hazards to illustrate how a relatively uncomplicated series of events can lead to workplace deaths and injuries. ...
"a. Fatalities in asphyxiating atmospheres. In its analysis of these confined space incidents, OSHA uses the term ‘asphyxiating atmosphere' when referring to an atmosphere which contains less than 19.5 percent oxygen. Oxygen levels under 19.5 percent are inadequate for an entrant's respiratory needs when performing physical work, even if the space contains no toxic materials.
There are many potential causes of asphyxiating atmospheres. For example, the oxygen in a space may have been absorbed by materials, such as activated charcoal, or consumed by chemical reaction, such as the rusting of a vessel or container. In another situation, the original atmosphere in the space may intentionally have been wholly or partly inerted using such gases as helium, nitrogen, argon, or carbon dioxide. Victims of asphyxiation often are unaware of their predicament until they are incapable of saving themselves or even calling for help. ...

OSHA provides guidance in a letter of interpretation dated March 30, 1999:

The type of testing that needs to be performed within a permit-required confined space is dependant on the hazards that are present within the space; employers are not required to test substances which will not potentially be present. As paragraph (d)(5)(ii)of 29 CFR 1910.146 states:
"(ii) Test or monitor the permit space as necessary [bold emphasis added] to determine if acceptable entry conditions are being maintained during the course of entry operations;

The standard's Appendix B - Procedures for Atmospheric Testing provides instruction on testing. The statement "If tests for toxic gases and vapors are necessary, they are performed last" would imply that an employer would not need to test for toxic gases and vapors if there is no potential for them to be present in the space.

1910.146(e)(6) states: "The employer shall retain each canceled entry permit for at least 1 year to facilitate the review of the permit-required confined space program required by paragraph (d)(14) of this section. Any problems encountered during an entry operation shall be noted on the pertinent permit so that appropriate revisions to the permit space program can be made.
"NOTE: Employers may perform a single annual review covering all entries performed during a 12-month period. If no entry is performed during a 12-month period, no review is necessary."

You may discard the cancelled entry permits after the review. However, keep in mind that OSHA's standard on access to employee exposure and medical records (1910.1020) requires the employer to maintain employee exposure records for at least 30 years. If you needed to monitor the entrants' exposure to toxic substances during the entry, OSHA expects you to keep a record of this exposure - see 1910.1020(d)(1)(ii) and 1910.1020(c)(5).

It's our understanding that OSHA would expect you to follow the equipment manufacturer's instructions for the instrument's calibration, use, and maintenance. You may also want to consult with an industrial hygienist for recommendations on air monitoring equipment selection and use.

In the permit-required confined spaces standard's Note to 1910.146(d)(5), OSHA states that "Atmospheric testing conducted in accordance with Appendix B to 1910.146 would be considered as satisfying the requirements of this paragraph. ..." In Appendix B - Procedures for Atmospheric Testing - paragraph (1) - Evaluation testing - states: "The atmosphere of a confined space should be analyzed using equipment of sufficient sensitivity and specificity to identify and evaluate any hazardous atmospheres that may exist or arise ... . Evaluation and interpretation of these data, and development of the entry procedure, should be done by, or reviewed by, a technically qualified professional (e.g., OSHA consultation service, or certified industrial hygienist, registered safety engineer, certified safety professional, certified marine chemist, etc.) based on evaluation of all serious hazards."

Other than directing the testing sequence for permit space air monitoring (see 1910.146(d)(5)(iii)), . OSHA expects the employer to follow manufacturer recommendations for making sure the test equipment is accurate. The manufacturer is an expert in their own product and would have the best direction on its care, performance, and maintenance.

An OSHA advisory safety and health information bulletin on Calibrating and Testing Direct-Reading Portable Gas Monitors states the following:

The International Safety Equipment Association (ISEA), founded in 1933, is a trade association for manufacturers of protective equipment, including DRPGMs. The ISEA recommends, at a minimum, verifying the operational capability of these instruments before each day's use, with additional testing conducted as necessary. This SHIB incorporates recommendations developed by the ISEA. ...
Standard procedures for regular calibration that conform to the manufacturer's instructions, internal company policy, and/or the appropriate regulatory agency guidelines will help to ensure that calibration procedures are readily followed by the DRPGM operators, and that the instruments are operable and accurate when used. Employers should keep calibration records for the life of each instrument. This record enables operators to quickly identify a DRPGM that has a history of excessive maintenance/repair, or is prone to erratic readings, and to track drift of the sensors to determine when they need replacement. [Editor's Note: It would be up to you to determine if and how you would want to keep equipment calibration logs. Calibration logs aren't required by OSHA, but they would be good evidence of your efforts to maintain the equipment.] ...
Bump Test (or Function Check)
This is a qualitative function check in which a challenge gas is passed over the sensor(s) at a concentration and exposure time sufficient to activate all alarm settings. The purpose of this check is to confirm that gas can get to the sensor(s) and that all the instrument's alarms are functional. The bump test or function check does not provide a measure of the instrument's accuracy. When performing a bump test, the challenge gas concentration should trigger the DRPGM's alarm(s).
Calibration Check or Full Calibration
There are two methods for verifying DRPGM accuracy: a calibration check and a full calibration. Each method is appropriate under certain conditions.
A calibration check verifies that the sensor(s) and alarms respond within the manufacturer's acceptable limits by exposing the instrument to a test gas. The operator compares the reading to the test-gas concentration (as indicated on the cylinder containing the test gas). If the instrument's response is within the acceptable range of the test-gas concentration (typically ± 10-20% of the test-gas concentration), then the calibration check verified the instrument's accuracy. (Note: OSHA recommends that operators check with the instrument's manufacturer for the acceptable tolerance ranges.) An operator should ‘zero' an instrument (reset the reference point, in some cases ‘zero air' gas may be needed) before conducting the calibration check to ensure that the calibration check results are accurate. When performing a calibration check, the test-gas concentration should be high enough to trigger the instrument's alarm(s).
If the calibration-check results are not within the acceptable range, the operator should perform a full calibration. A full calibration adjusts the instrument's reading to coincide with a known concentration (i.e., certified standard) of test gas. Test gas used for calibration gas should always be certified using a standard traceable to the National Institute of Standards and Technology (NIST).
When to Perform a Bump Test and When to Perform a Full Calibration
In the past, there has been some confusion regarding proper calibration procedures and frequency. To clarify this issue, ISEA updated its position statement on instrument calibration in 2010, stating, ‘A bump test . . . or calibration check of portable gas monitors should be conducted before each day's use in accordance with the manufacturer's instructions.' If an instrument fails a bump test or a calibration check, the operator should perform a full calibration on it before using it. If the instrument fails the full calibration, the employer should remove it from service. Contact the manufacturer for assistance or service.

In the January 14, 1993, preamble to the final rule on permit-required confined spaces. OSHA states the following in a discussion of 1910.146(d)(4):

Regarding the use of specific material monitors (such as those for CO, CO2, SO2, and H2O), NIOSH recommended adherence to manufacturer's instructions concerning temperature limits, relative humidity ranges, and any known chemical interferences. The NIOSH comment also contained information and recommendations concerning non-specific monitors.
NIOSH concluded its comment with recommendations concerning the care of batteries used in monitors and a strong emphasis on the proper calibration and maintenance of monitoring equipment. NIOSH also concluded that operator training and skill levels are very important factors to be considered in the monitoring of workplace atmospheres, to the extent that such monitoring cannot be effectively accomplished without a trained and skilled operator.
OSHA has concluded, based upon the information received in response to the questions asked in hearing Issue 4, that the accuracy of testing and monitoring equipment may be significantly affected under certain conditions of humidity, pressure, or temperature or by the presence of interfering chemicals. However, if the equipment is properly selected, calibrated, and maintained and if it is operated by well trained employees, the testing and monitoring needs for entry and work in permit-required confined spaces can be effectively met.

Section II of OSHA's Technical Manual is an in-depth study of sampling, measurement methods, and instruments. The manual suggests following the equipment manufacturer's instructions for calibration.

Because the hazards of permit spaces vary from space to space, and from entry to entry, OSHA's standard includes no detailed specifications for necessary entry access/rescue equipment. If employers choose to use local emergency management resources, like the fire department’s rescue team, conduct a mock-scenario and verify their response time. It’s common for many fire department rescue teams to be volunteers and they could take many hours to respond because they may not be responding from the fire station.

OSHA does, however, provide some guidance on rescue equipment in Section III of the preamble to the final rule published in the Federal Register in January 1993. It summarizes some of the comments OSHA received concerning the use of powered winches to provide rescue:

Paragraph (k)(3)(ii) requires the outside end of the retrieval line to be attached to a fixed point or a lifting (or other retrieval) device in such a manner that rescue can begin as soon as the rescuer (in most cases the attendant) becomes aware that rescue is necessary. (As noted earlier, the attendant is only allowed to participate actively in non-entry rescue.) A mechanical device is required for vertical permit spaces more than 5 feet deep. ...
Additionally, some commenters addressed the advisability of using powered winches to remove authorized entrants from permit spaces. One commenter (Ex. 14-54) stated:
Used powered winches, overhead cranes, etc. is the easiest way to impale victims, tear off limbs and retrieve pieces and parts of victims. The word ‘Rescue' means to remove a victim from danger to safety, not to add danger.
Also, Caterpillar, Inc. (Ex. 14-137) commented:
Power [winches] will not be used where additional harm to employees may occur.
Another commenter (Ex. 14-166) stated:
Powered retrieval winches should be recommended where depths exceed 50 ft and should be equipped with torque limiters of approx. 450 lbs to avoid damaging the incapacitated person.
Frank Rapp of the UAW testified (Chicago Tr. 440):
Some plants we usually [use a] fork truck, attach the lifeline onto the fork over a pit and lift them up by fork truck. You can do an extreme amount of damage to that person as they're ricocheting off a wall coming up.
ANSI Z117.1, Section 12.2.1 requires a mechanical device to be available to retrieve personnel from vertical type permit spaces greater than 5 feet in depth (Ex. 129).
"OSHA believes that there are circumstances where the attachment of a retrieval line to a fixed point would enable the attendant or other rescue personnel to safely extract an entrant without the need to enter the space. OSHA further recognizes that a mechanical device will usually be necessary to enable rescuers outside the space to lift entrants out of vertical permit spaces. Therefore, the OSHA has adopted the ANSI approach requiring a mechanical device to be available, if a retrieval system is used, during entry operations involving vertical type permit spaces more than 5 feet deep. (Any permit space whose opening is above the entrant is considered to be a ‘vertical-type permit space.') The mechanical device used should be appropriate for rescue service. The employer should not use any mechanical device, such as a fork lift, that could injure the entrant during rescue.

You may want to review the following industry consensus standards for guidance on recognized safe practices:

ANSI Z117.1 - Safety Requirements for Confined Spaces
ANSI Z359.4 - Safety Requirements For Assisted-Rescue And Self-Rescue Systems, Subsystems And Components
NFPA 1983 - Standard on Life Safety Rope and Equipment for Emergency Services.

Under 1910.146(k)(3) OSHA requires: "To facilitate non-entry rescue, retrieval systems or methods shall be used whenever an authorized entrant enters a permit space, unless the retrieval equipment would increase the overall risk of entry or would not contribute to the rescue of the entrant. Retrieval systems shall meet the following requirements. ..."

Section III of the preamble to the final rule published in January 1993 includes the following:

In enforcing this provision, OSHA will inspect the permit space to determine whether or not a retrieval system would contribute to a rescue without increasing the overall risk of entry. The Agency will use the following guidelines to make this determination:
(1) A permit space with obstructions or turns that prevent pull on he retrieval line from being transmitted to the entrant does not require the use of a retrieval system.
(2) A permit space from which an employee being rescued with the retrieval system would be injured because of forceful contact with projections in the space does not require the use of a retrieval system.
(3) A permit space that was entered by an entrant using an air supplied respirator does not require the use of a retrieval system if the retrieval line could not be controlled so as to prevent entanglement hazards with the air line.
Paragraphs (k)(3)(i) and (k)(3)(ii) set forth requirements for the proper use of retrieval systems. Paragraph (k)(3)(i) requires the authorized entrants to wear a chest or full body harness with retrieval line attached. The point of attachment of the retrieval line must be at the center of the entrant's back, near shoulder level, or above the entrant's head so that the entrant will present the smallest possible profile during removal, in case a rescue becomes necessary. The use of wristlets in place of the full body harness is recognized, if their use is appropriate (that is, if a full body harness cannot be used because of the configuration of the space). ...

OSHA's compliance directive, CPL 02-00-100 [CPL 2.100] - Application of the Permit-Required Confined Spaces (PRCS) Standards, 29 CFR 1910.146, includes the following guidance in Appendix E:

When practical, non-entry rescue is required by paragraph (k)(3) of the standard and is the preferred method of rescue, even for horizontal entries. OSHA recognizes that the danger of entanglement due to lifelines or lanyards snagging or obstructions within a permit space may be greater for horizontal permit spaces than for vertical spaces.