Follow-up (or Verification) is the visual inspection or proof of conformity through sampling, measuring, laboratory testing, or document review. Verification is intended to proof the good use of UL marks awarded, as well as the continuous compliance of the product with safety and/or functionality requirements specified in regulatory documents and requirements in the modality or scheme under which the product has been certified. The validity of the product certificate or opinion issued depends on the result of the verification.

Verification (follow-up) visits have been classified into the following types:

  • Pre-inspection visit: it is made with advance notice as a prerequisite for product certification under Certification Modality II
  • Routine inspection (in-site) visits: they are made to take the required sample (s) to verify that the product continues to comply with the tests and specifications under which the certificate was given. They apply to all modalities. These visits do not require confirmation and may be made in accordance with UL’s availability for the following three months from the date on which the corresponding Notice is sent. However, these visits may be made in some cases with advance notice to the contact person.

These visits may also be made in order to assess the Quality Management System (QMS), according to the requirements set forth in the applicable certification scheme.

  • Extraordinary visits: they are made with or without advance notice, depending on the case, either to verify the implementation of corrective measures for previously detected non-conformities and do the product sampling required, or when required by authorities owing to a complaint received by third parties. They apply to any certification modality and are scheduled at the express request of the certification area or you, or at the express request of agencies or competent authorities.

Important points to keep in mind:

  • UL schedules verification visits within the validity period of certificates issued.
  • UL will notify you of a verification visit. In case of visits with advance notice, if we do not receive the confirmation requested within the time indicated by UL, the visit will be accepted on the date and place scheduled.
  • If there is a problem with the date and place indicated in the notice, the legal representative and/or contact person shall request the rescheduling of the visit within the period indicated in the notice, as applicable. The visit may be rescheduled at most once.
  • Please remember that the customer, manufacturer, owner, their subordinates or managers of industrial or commercial establishments are responsible for allowing access and making easy for UL’s staff to carry out the verification visit.
  • Sample (s) selected shall be sent to a laboratory subcontracted and/or validated by UL de México, S. A de C.V., or a laboratory with which UL de México, S.A. de C.V. has signed an Acuerdo de Reconocimiento Mutuo (‘MRA,’ Mutual Recognition Agreement in English).
  • If this is the case, we shall respond to non-conformities found within the time limits stipulated in the corresponding notice. If necessary, extraordinary verification visit (s) will be made to review the implementation and effectiveness of corrective actions taken.
  • Any product changes or modifications shall be reported or notified in writing to UL. In turn, UL will analyze and, if applicable, request additional product testing to confirm that the product continues to meet safety and/or functionality requirements in the applicable standard.

Activities during One Verification (On-Site) Visit include:

  • Description of the scope of the verification visit and, if applicable, identification of the people taking part in the verification.
  • Document review only for Modality II.
  • Quality System and Production Line audit for Modality II.

Product sampling:

Sampling is strictly made with the quantities required for the tests required by the applicable standard. The number of samples is selected in duplicate given that one of the samples will be considered a “blank sample.” The customer may choose not to handle a blank sample. In this case, the customer shall indicate it at the time that the UL representative conducts product sampling. The blank sample will be used in case of doubt or controversy or when the result of the technical analysis is negative. The blank sample shall be safekept by the customer and will be invalid once UL has issued a favorable response. If you decide not to provide a blank sample but it is required during the process, you should ask UL for an extraordinary verification visit for product sampling. UL will make the extraordinary visit and bill you for it.

The first verification will be made on the sampled product. If the result is positive, UL will generate the corresponding ‘Notice of Compliance (NOC).’ If not, UL will notify you in writing of the certificate suspension.

If the result of the first sample is negative and there is a blank sample, the blank sample shall be sent for testing within the established time period and UL shall be notified of this situation.

  • If the certificate issued contains more than one product model, untested or pre-sampled product samples should preferably be taken.
  • Product marking review and mark usage.
  • Activity overview: UL’s representative will fill in the Inspection Report, summarize and, if applicable, explain the remarks and/or deviations found. UL’s representative will give you an (electronic or printed) copy of the ‘Inspection Report’ for your reference.


UL has established different time periods (deadlines) for activities in which a response is required by the customer.

Deadlines are considered from the day after the customer received the corresponding notice or the date on which the verification visit was made.

Period of time for the activity to be carried out Type of visit
5 business days to confirm an unscheduled visit.
3 business days to confirm a visit with advance notice.
45 calendar days to register Sampled-Product Test Result Reports.
30 calendar days to register the Blank-Sample Test Result Reports. ●* ●*
Blank sample safekeeping by the customer *
5 business days to send the blank sample to the laboratory, if applicable.
5 business days to request a verification (in-site) visit.
5 business days to inform UL in writing of the corrective actions to be taken.
30 calendar days or the period established by UL de México, S.A. de C. V for the closing of non-conformities detected.

*           The blank sample is invalid once UL de México, S.A. de C.V. has issued a favorable response