@MattD2 There isn't an international standard that I know of. Our company works with the three biggest fuel companies in New Zealand (International and National companies) and they all have their own system, which have some similarities, though many differences.

For our internal permit to work system, that we apply to our customers without their own PTW system, we closely align with one of the customer systems.

Here is a good reference: https://z.co.nz/ptwinfo

Thanks for the reply @Chris Anderson - that is where my digging has got to too. Seems like there is common process in the petrochemical industry on PTW, which is why I originally mentioned DuPont as they seem to be one of the leading players when PTW systems were becoming common place. These also seem to have been adopted to certain extents by medium industrial / manufacturing companies. But then there are some widely different processes by other industries (such as NZ electrical generation/transmission).
With it being common in NZ for contractors to work over a large variety of industries I do feel for them having to be up-to-speed on multiple processes for the same type of work depending where they are... and no wonder it can be a struggle to get some contractors to "follow the rules" when it can be completely different to what had been ingrained in them depending on where they have spent most of their time... however as for solutions, I do not have any just right now unfortunately.

I have searched my database and found the following. Some are ancient and some are reports of events. Two in bold are joint Australia/NZ standards and may be relevant and available.
There used to be a common permit system in Taranaki for the oil & gas industry.
Hope that's some help
DoL. (1985). Dust Explosions in Factories: precautions required with combustible dusts. Wellington: Department of Labour.
DoL. (1988). Hot Work on Drums and Tanks. Wellington: Department of Labour.
Wakakura, M., & Tamura, M. (1991). Explosion and fire caused due to insufficient purging during inspection work on a continuous extractor. Retrieved 22 December 2014, from http://www.sozogaku.com/fkd/en/cfen/CC1000088.html
HSE. (1995). Hot work in docks. Information Sheet Sudbury: HSE.
SA AS 1674.1:1997. Safety in welding and allied processes Part 1: Fire precautions. Sydney: Standards Australia.
HSE. (2000). Hot work on small tanks and drums. Information Sheet Sudbury: HSE. Retrieved from www.hsebooks.co.uk
CSB. (2001). Refinery Incident – Motiva Enterprises LLC. Incident Investigation report 2001-05-I-DE Washington, DC: Chemical Safety and Hazard Investigation Board. Retrieved from http://www.csb.gov/
SA/SNZ2865:2001. Safe working in a confined space. Wellington: Standards New Zealand.
GAPS. (2003). Cutting, welding and other hot work. Guidance Note Avon, CT: Global Asset Protection Services.
Manz, A. (2003). Welding, cutting and other hot work. In Cote, A., Hall, J., Powell, P. & Grant, C. (Eds.), Fire Protection Handbook (19th ed., pp. 6-211 - 216-220). Quincy, MA: National Fire Protection Association, Inc.
HSE. (2005). Guidance on permit-to-work systems: A guide for the petroleum, chemical and allied industries. Guidance Note: General Series Sudbury: HSE Books. Retrieved from http://books.hse.gov.uk/
DoL. (2006). Health and Safety in Welding. Wellington: Department of Labour.
FM Global. (2006). Hot work management. Property Loss Prevention Data Sheet Johnston, RI: Author. Retrieved from http://www.fmglobal.com
GAPS. (2009). Loss prevention and control for cutting, welding, hot work operations. Guidance Note Avon, CT: Global Asset Protection Services.
HSE. (2009). Safe work in confined spaces. Guidance Note Sudbury: HSE Books. Retrieved from http://books.hse.gov.uk/
Hayes, J. (2010). Safety Decision Making – Drawing a Line in the Sand. Working Paper 74 Canberra: Australian National University. Retrieved from www.http://ohs.anu.edu.au/
Marmo, L., Piccinini, N., Russo, G., et al. (2013). Multiple Tank Explosions in an Edible-Oil Refinery Plant: A Case Study. Chemical Engineering & Technology, 36(7), 1131-1137.
Burlet-Vienney, D., Chinniah, Y., Bahloul, A., & Roberge, B. (2015). Occupational safety during interventions in confined spaces. Safety Science, 79, 19-28.
Jahangiri, M., Hoboubi, N., Rostamabadi, A., et al. (2016). Human Error Analysis in a Permit to Work System: A Case Study in a Chemical Plant. Safety and Health at Work, 7(1), 6-11.

Thanks Chris - some good references there. Yes I was aware of the regional permit system for the petrochemical sites in/around Taranaki - do I understand you correctly that this is no longer in use (it's been a good 4 or so years since I have looked at it)?

I cannot speak to the current status of the Taranaki common permit. I knew about it 2000-2003 when I was the corporate Risk Manager for what was then Natural Gas Corporation. Your knowledge is therefore more up to date than mine.
Maybe someone else in the forum with current knowledge can comment?

The common permit system is still up and running in Taranaki. Not sure who is overseeing it these days with all the changes in field ownership etc over the last few years.