However, as stated in the Code of Safe Working Practices the permit to work does not by itself make the job safe but is only one aspect of a safe operation. This is an important consideration. Work can be executed safely only through the combined efforts of those involved in planning the job, authorizing it, supervising it and those who are performing the job. The personnel involved in performing the work activity are usually at the sharp end and most exposed to the hazards if something were to go wrong.
There may be items in the permit which maybe indicated as having been checked without the responsible person actually checking them or the conditions at the work site may change unbeknown to the crew. Let’s look at the example of entry into a ballast tank for which a permit has been issued. Will the crew, who have to enter the space for inspection or maintenance, make an entry without testing the atmosphere and satisfying themselves that it is safe, or do so without carrying portable gas detectors? Perhaps not. The persons carrying out and supervising the task cannot purely rely on the permit to work and assume all is well. They will be required to do their own checks before commencing the job and be alert to any possible changes in work conditions for the duration of the work.
A permit to work is no doubt of vital importance for high risk activities, but it is not a replacement for the basic safety checks which the crew must carry out themselves before and for the duration of the job.
Source: Gard (http://www.gard.no/web/updates/content/29725119/a-permit-to-work-contributes-to-safety-but-you-make-a-job-safe)