Question - Drain Gas Safety

[Caver]

I'll start by introducing myself. I'm a caver and have always liked underground stuff. I recently found the main outflow from a storm drain near my house and have become obsessed by it. Looking in through the bars with it passing under the underpass which is passing under the road looks so interesting. Knowing there is a network under the city I have to explore it.

I think being a caver and having been in the occasional mine I can handle most things but the one thing I need advice on is gas. How likly am I to come up against this, what gas detectors an other equipment should I use and any other advice would be appreciated. All thing relating to gas safety.

 

[The Kwan]

Welcome to the forum mate, if it has an outfall then it will likely have an infall which probably means that it has air flow so sounds promising, most folk seem to use a 4gas detector for gas detection.
What city?

 

[Punk]

Welcome, always good to see a fellow underground explorer.
Storm drains are relatively safe with gases, I've only come across one that I've not been happy with gas wise, and left immediately. Smell eggs? Get out. Sewers is where the real risk lies, but don't be complacent. I'm a relative noob to this, @Ojay would be the best help on here for this.

 

[Punk]

Welcome, always good to see a fellow underground explorer.
Storm drains are relatively safe with gases, I've only come across one that I've not been happy with gas wise, and left immediately. Smell eggs? Get out. Sewers is where the real risk lies, but don't be complacent. I'm a relative noob to this, @Ojay would be the best help on here for this.

 

[Caver]

What city?

It's in Dundee Scotland. I've attached pictures I took quickly of the outside. Still not been in it. It narrows quickly to a tube that is probably about 1m high and when I get in it I will report on what's past that.

EDIT: IMAGES/ATTACHMENTS NOT WORKING