This will probably be one of the most annoying/trickiest achievements in the game but it's by far doable, I got it on my second dedicated run. There is a lot of trial and error and being experienced with the game certainly helps; for context, this was my last achievement to get 100%!
The premise of the achievement is as stated is to not allow your workplaces to fall into either the "Safe" or "Deadly" levels. The safety levels break down into 5 levels;
1 - SAFE
2 - Unhealthy
3 - Harmful
4 - Dangerous
5 - Deadly
We will control the state of safety in our workplace by using the ventilation plants primarily. Each of them allows us to raise the safety of the workplaces with them turned on (-1 to the danger level) or lower it if needed. You will want to get the maximum of the ventilation plants as soon as possible to aid.
Firstly, start up a scenario on "The Last Autumn" and customize it to make it Easy difficulty (You can play harder if you need that challenge!). Firstly will be my tips and the "do's and don'ts".
- Do not research any safety procedures from the workshop! when you've passed the gas phase all your workplaces will be safe if you do, which is bad!
- You'll probably need the safety rafters only once or twice, but you will definitely need those, so don't forget to research them.
- When prompted who to side with, go down the worker route and build the Labour Union so you can easily manage your safety levels in one place and attempt to solve the strikes!
- Whenever you can try and aid production by 20% using the Supercharge ability; Resource pending of course.
- I aimed to have the workplaces floating at the 'harmful' level, that way it can go either way.
- Save frequently, normally at the start of every day or after each milestone is met for the construction. I reverted a few times to either my save or an autosave and still got the achievement.
- Do not make any laws that improve safety, avoid the 'safety procedures' law where possible.
Now, onto breaking the entire scenario down into stages which I will go through below;
Initial/Building Stage -
The game will initially not involve safety so this is your time to get your settlement built and sustainable, focus on your resource gathering, and not too much about the generator. I had a fair settlement before I'd built anything within the central ring. The game will involve safety by roughly day 5. Although, if you don't have any workplaces then they can't be dangerous!
Make sure at this point that any ventilation plants you have are turned off and are set to 24 Hours as the workplaces will start in the 'Unhealthy' level and your vents can knock it down to 'safe' if they're turned on.
Once your ready, start your inner workplaces, I had encircled around the generator plot; 3 Ventilation plants and 2 of each workplace providing the needed construction pieces. Then start the construction of the generator.
Once you have started the generator you will have both areas to contend with, the generator will be a more dangerous place to work than the outer workplaces so it's a careful balancing act if the safety levels go too low, then turn off a vent or two to increase it, if it rises too high, then turn them on to lower it.
Gas Phase -
At around day 7 (for me at least) the game will introduce the gas. This will rise and fall by the day and changes at roughly 6:00 am. You can see whether it will go up or down under the temperature gauge so you can preempt the safety level for each day.
This stage is where we will be spending most of the game, try and focus most of your effort on getting that generator built! The less time spent actually constructing means less time managing two different levels with them going up and down. A good tactic I used would be to gather the resources needed for all the generator parts and then steal your manpower from factories and put all hands to work on the generator to get it done ASAP!
Throughout you will be dealt with decisions on the generator, most of them won't affect the safety levels but you will ultimately have to sacrifice workers or lose progress on the generator. I chose to sacrifice the workers every time. To counter this when I had the telegraph station I was constantly calling in new workers with the occasional engineer.
Just before the final part of the generator within a milestone is to be completed make sure that you save your game. When you've placed down the next piece(s) if you don't have the correct amount of vents to adjust the levels it can throw you into the 'deadly' zone. If it does, memorize how many you will need and then reload the save and adjust as necessary.
There will potentially be the odd time where the safety levels of the factories are 'Unhealthy' whilst the generator stages are 'Dangerous' and the gas levels are due to change which could throw either into the unwanted zone. If you encounter this situation then make use of those Protective structures to help out.
To add to things your workers will go on strike occasionally due to the poor conditions. If this happens you may be prompted with a solution (Raise safety/Enact a law/ ). When I was given this I would normally opt to improve safety and then use the protective structure and fill the place with workers hoping to gain as much progress before the ability expired. The workforce will immediately go back on and it will be a matter of waiting until the ability is ready again. If you max the workforce you can normally finish construction.
Post Gas Finish -
If you didn't research any safety improvements then when the gas has been sealed off with the completion of the core all of your workplaces should be placed at the "unhealthy" level. From here it's fairly plain sailing to finish the generator as safety levels shouldn't change. You'll only have the occasional strike to contend with.
After the generator is completed you'll be prompted to either stay and advance the generator or leave. The choice is yours but if you leave then the game will end and *fingers crossed* if you've managed those safety levels correctly then the achievement should pop during the finale.
If you have any questions, then ask away and I'll offer what advice I can!