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The most useful format for generic PM procedures

(This document was last revised on 10-1-18)


5.1 Introduction

There has been considerable debate about the form and content of PM procedures; specifically about whether or not they should follow the exact form and content of the procedure that is provided by the device manufacturer. We believe that there is little merit in requiring this. The PM procedures provided by the manufacturers come in a range of different formats and in many levels of detail and complexity. Some are quite concise and suitable for using in the field as a guideline and checklist. Others are integrated into lengthy, detailed technical manuals that are useful for training purposes but not practical for day-to-day use in the field.

It is important that the maintenance procedure include a complete set of device restoration tasks for restoring (i.e. cleaning, reconditioning, refurbishing or replacing) all of the device’s non-durable parts. The first place to check on which of the device’s parts may be considered non-durable is the manufacturer’s own PM procedure (if one is available). In the event that there is no manufacturer procedure available, the next best resource would be any other generally available procedure for this same type of device or any similar source of general industry knowledge. For example, see the list of device restoration tasks for an anesthesia machine (ANES-01)

It is very important that the maintenance procedure also include a complete set of safety verification tasks that will confirm (or not) that all of the device’s potentially critical failure modes (those that would lead to worst case adverse outcomes) have been checked or tested. For example, in the case of an apnea monitor, which has been classified as safety verification-critical at the life-threatening level, the sensor not detecting a reduced air flow and the alarm component failing, have been identified as two critical failure modes. Therefore the maintenance procedure should include separately numbered line-item tasks to confirm that the breathing detector is operating within its specified performance specifications and that the alarm or notification device is performing properly. The maintenance documentation should note the results of testing for the proper functioning of these two components separately so that subsequent analysis of the maintenance records will allow separate computation of the failure rates of each of these two potentially critical hidden failures. See the proposed generic procedure for an apnea monitor (APN.M-01)

5.2 Standardized format for PM Procedures

The Task Force has developed a simple, standardized format that we are asking all maintenance entities participating in this project to use. If other forms of procedure are used they must, as a minimum, cover the same list of TPM and SVT tasks as the corresponding HTMC procedure and include the same reporting format. The current version of Table 4 contains several sample HTMC procedures (AED-01, ANES-01, C.VEN-01, etc). These can be viewed by clicking on the HTMC PM Procedure code in the last column. The HTMC PM Procedure format has the following important features:

  1. Unlike some of the manufacturer versions the format of the procedure is a simple, clearly worded list of standardized task statements.
  2. There are separate lists of device restoration tasks (to address the rejuvenation of any of the device's non-durable parts) and safety testing tasks (to detect any hidden performance or safety degradations) that are considered to be critical - critical in the sense that not performing them in a competent and timely manner could lead to a serious adverse outcome.
  3. It uses the same simple, consistent terminology used in all of the HTM Community documents
  4. The concise, 6-character procedure code ties the procedure to a device at the manufacturer-model level. This code is specifically customized to this particular manufacturer-model version of the device type. However, it may not be unique to this particular version. The same version of the code may be appropriate for a number of different manufacturer-model versions of the same type of device but there may also be different versions of the procedure for, say, a defibrillator - that reflect differences in the tasks needed when the device is being used in, say, a particularly hard use environment such as an ambulance rather than at a hospital bedside. This “hard-use” version of the procedure might be coded DEF-02 rather than the standard DEF-01. The hard-use version may also call for a different (shorter?) PM interval.
  5. The scope of the list of device restoration tasks is made scrupulously consistent with the scope of the manufacturer-provided PM procedure.
  6. Similarly, the scope of the list of safety verification (hidden failure detection) tasks is also made totally consistent with the scope and content of any manufacturer-provided PM procedure and with any other known critical failure modes that might not be included in the manufacturer-provided procedure.
  7. Each of the tasks that are judged to be potentially critical are annotated with a statement in red indicating a judgement on the worst-case severity of the potential adverse effect (Life-threatening/ possible patient injury/ or possible disruption of care) if the device should require either an unusual level of restoration, or should fail the performance or safety test.
  8. A specially-formatted reporting section at the end of the procedure prompts the technician to capture all of the findings from the device restoration and safety testing tasks using a simple, intuitive form of coding (see section 5.3 below.

5.3 Condition rating the device based on the PM findings

(Material copied over from Section 1.7 of HTM ComDoc 1).

In the recommended format of each HTMC generic PM procedure (see column 7 of Table 4) a reporting section is added at the bottom of the procedure asking the service person to indicate by circling one of three letters (A, B or F) whether or not the performance and safety testing of the device revealed any significant degradations (latent MR1 failures) or any hidden failures.

PM Code A = nominal. The letter A should be circled when the results of all of the PVST tests were in compliance with the relevant specifications, and any other functions tested were within expectations.
PM Code B = minor OOS condition(s) found. The letter B should be circled when one or more conditions were found that were slightly out-of-spec (OOS) or slightly outside expectations. The purpose of this B rating is to create a watch list to monitor for future adverse trends in particular performance or safety features, even though the discrepancy is not considered to be significant at this time. An example of this would be an electrical leakage reading of 310 microamps which is within 5% of the 300 microamp limit. A B rating should be considered a passing grade.
PM Code F = serious OOS condition(s) found. The letter F should be circled when one or more performance or safety features is found to be significantly out-of-spec. (OOS). This is a failing grade and, if it is a high-risk device, it should be removed from service immediately.

The service person is also asked to indicate by circling one of four numbers (1, 5, 9 or 0) the physical condition in which the device parts that were rejuvenated by the traditional PM tasks were found. The numerical ratings should be circled to indicate one of the following findings.

PM Code 1 = better than expected. There was very little or no deterioration; i.e. the physical condition of the restored part was found to be still good.
PM Code 5 = nominal. There was some minor deterioration but no apparent adverse effect on the device’s function; i.e. the physical condition of the restored part was found to be about as expected.
PM Code 9 = serious physical deterioration. The restored part was already worn out and probably having an adverse effect on device function; i.e. the physical condition was found to be considerably worse than expected.
0 = no physical restoration required. The device has no parts needing any kind of physical restoration.

If the PM findings are systematically documented each time a PM is performed, then aggregated into a PM Findings database, it will be possible to:

  • get an indication of the mean time between failures (MTBFs) of any hidden failures, and
  • get an indication of how well the PM interval matches the optimum - which would be when the part being restored has deteriorated - but only to the point just before the deterioration begins affecting the functioning of the device.
  • A preponderance of PM Code 1 findings would indicate that the interval is too short; and
  • A preponderance of PM Code 9 findings would indicate that the interval is too long.
  • A preponderance of PM Code 5 findings would indicate that the PM interval is just about right.

5.4 Recommended actions based on the PM findings


PM Findings coded as:

  • A combined safety verification and wear rating of A5 – No action required.
  • Safety verification rating of F (failed because a serious OOS condition(s) found) - If the PM Task that is given the failing grade "F" is labelled with the statement "(Serious failure is potentially Life-Threatening)" the device should be removed from service immediately.
  • Safety verification rating of B (minor OOS condition(s) found) – Make a note to watch for any further deterioration in this particular performance or safety feature at the time of the next PM.
  • A preponderance of PM Code 1 findings (still good) – Consider changing to a shorter PM interval.
  • A preponderance of PM Code 9 findings (already worn out) – If this is a consistent finding, and the device is judged to be maintenance-critical, consider reducing the length of the PM interval.

5.5 PM-critical and non PM-critical classification based on the likelihood of the device having PM-related critical failure modes


To be completed.


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