Here's what I found comparing the two products so far.
Ospho has a safety sheet document [pdf file] on their site with the hazardous information about the product. Ospho has an acidic smell is an eye, skin and lung irritant. It creates a gas while it's working that releases a strong smell into the air.
This is the problem. Our homebase is Oregon, but we are here in California for a while doing a project. We are staying in a park and wanted to take care of a little rust on the bumper without causing problems with those who are parked permanently around us. A lot of people do small projects on their rigs - nothing major is allowed - but painting or polishing is ok, so we had to find a product that wouldn't become an irritation to anyone with toxic fumes or was hazardous to pets or people and didn't need to be rinsed.
I have also gone to the sites of everything suggested here so far and looked up the safety info. Naval Jelly has to be washed off and presents a threat to water supplies, nearby creaks etc.
I also looked up the safety sheet on Rusteco and it's far better than Ospho, but still includes the following:
Prolonged exposure to vapor or mist may cause irritation in eyes, nose, mouth and/or throat. It warns against using in an enclosed environment. And also that there is the danger of combustion under certain conditions.
The rest of the specs on Rusteco are pretty respectable environmentally speaking, but it does present some possible problems if over-exposed and fumes while it's working.
The following is directly from The Rust Doctor site:
Non Toxic and Non Flammable!
There are no solvents or strong acids in Rust Doctor. This allows you to restore rusty surfaces without the fear of toxic fumes or potential skin irritation. Rust Doctor can be sprayed in an enclosed environment without the need for special breathing equipment. Clean-up after using Rust Doctor is easy and only requires washing brushes and spray equipment with soap and water. Rust Doctor is a one step process and does not require any chemical preparation of the rusty metal or rinsing after it is applied. Shelf life is two years and the container can be opened and closed as many times as necessary. And, unlike many other solvent-based rust paints, Rust Doctor is completely non-flammable! It is an ideal product for customers who are concerned about the risk of fire whether at home or at the workplace.
The different methods of delivering rust to an oxidated stage of magnetite or another variation is unique in each product.
I've even found products that say their environmentally friendly but present lots of problems for the user that wouldn't be possible for us to use in this circumstance - this was a tough search and I was honestly surprised to find anything that would make it possible to do this in an occupied environment.
Most interesting to follow up on products posted here!
[currently in California]