As long as you aren't combining it with other depressants like benzodiazepines or alcohol, chasing is the safest method for heroin use. Since you feel the high pretty much instantly, you can understand if you have had enough within a minute at most. If I were you, I would chase a third of it without rushing and enjoy and understand your state for about ten minutes without smoking. After that, if you think you need more smoke another third slowly. You will know when you have enough.
If you don't combine with other depressants and if there's no fentanyl kind of substance in it, it's very hard to od when you chase heroin. One tends to nod heavily before being able to smoke enough to overdose. Still be careful and don't rush. Finally if you combine with stimulants like meth, keep in mind that they tend to mask the sedation which comes with heroin. This may cause you to use more heroin thinking that you haven't used enough. You could consume more H than you need because of that and get sick.
Take vare, good luck.